zhuhjay
22e48d9558
- 新增 .drone.yml 文件用于定义 CI/CD 流程 - 配置了基于 Docker 的部署步骤 - 设置了工作区和卷映射以支持持久化数据 - 添加了构建准备阶段和 Docker 部署阶段 - 定义了环境变量和代理设置 - 配置了 artifacts 目录的处理逻辑 - 添加了 timezone 映射以确保时间同步 - 设置了 docker.sock 映射以支持 Docker in Docker
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<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></div> <!----></nav> <ul class="sidebar-links"><li><a href="/blogs/java/java8/java8-1.html" class="sidebar-link">JDK8 特性（一）</a></li><li><a href="/blogs/java/java8/java8-2.html" class="sidebar-link">JDK8 特性（二）</a></li><li><a href="/blogs/java/java8/java8-3.html" aria-current="page" class="active sidebar-link">JDK8 特性（三）</a></li><li><a href="/blogs/java/java8/java8-4.html" class="sidebar-link">JDK8 特性（四）</a></li></ul> </aside> <div class="password-shadow password-wrapper-in" style="display:none;" data-v-59e6cb88 data-v-7dd95ae2><h3 class="title" data-v-59e6cb88>JDK8 特性（三）</h3> <!----> <label id="box" class="inputBox" data-v-59e6cb88><input type="password" value="" data-v-59e6cb88> <span data-v-59e6cb88>Konck! Knock!</span> <button data-v-59e6cb88>OK</button></label> <div class="footer" data-v-59e6cb88><span data-v-59e6cb88><i class="iconfont reco-theme" data-v-59e6cb88></i> <a target="blank" href="https://vuepress-theme-reco.recoluan.com" data-v-59e6cb88>vuePress-theme-reco</a></span> <span data-v-59e6cb88><i class="iconfont reco-copyright" data-v-59e6cb88></i> <a data-v-59e6cb88><span data-v-59e6cb88>ZhuHJay</span>
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<span data-v-59e6cb88>2021 - </span>
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2025
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</a></span></div></div> <div data-v-7dd95ae2><div data-v-7dd95ae2><main class="page"><section style="display:;"><div class="page-title"><h1 class="title">JDK8 特性（三）</h1> <div data-v-8a445198><i class="iconfont reco-account" data-v-8a445198><span data-v-8a445198>ZhuHJay</span></i> <i class="iconfont reco-date" data-v-8a445198><span data-v-8a445198>2022/5/25</span></i> <!----> <i class="tags iconfont reco-tag" data-v-8a445198><span class="tag-item" data-v-8a445198>JDK8</span></i></div></div> <div class="theme-reco-content content__default"><h2 id="_1-stream流-续"><a href="#_1-stream流-续" class="header-anchor">#</a> 1 Stream流-续</h2> <h3 id="_1-7-并行的stream流"><a href="#_1-7-并行的stream流" class="header-anchor">#</a> 1.7 并行的Stream流</h3> <ul><li><p>串行的Stream流</p> <ul><li>目前我们使用的Stream流是串行的，就是在一个线程上执行。</li></ul></li> <li><p>并行的Stream流</p> <ul><li>parallelStream其实就是一个并行执行的流。它通过默认的ForkJoinPool，可能提高多线程任务的速度。</li></ul></li></ul> <h4 id="获取并行stream流的两种方式"><a href="#获取并行stream流的两种方式" class="header-anchor">#</a> 获取并行Stream流的两种方式</h4> <ol><li>直接获取并行的流</li></ol> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">StreamParallelTest</span> <span class="token punctuation">{</span>
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<span class="token annotation punctuation">@Test</span>
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<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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<span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 直接获取并行的流 </span>
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<span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> stream <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">parallelStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><ol start="2"><li>将串行流转成并行流</li></ol> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">StreamParallelTest</span> <span class="token punctuation">{</span>
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<span class="token annotation punctuation">@Test</span>
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<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">serialToParallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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<span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">9</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">34</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">21</span><span class="token punctuation">,</span> <span class="token number">56</span><span class="token punctuation">,</span> <span class="token number">9</span><span class="token punctuation">)</span>
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<span class="token comment">// 转成并行流</span>
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<span class="token punctuation">.</span><span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
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<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>i <span class="token operator">-></span> <span class="token punctuation">{</span>
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<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">"::"</span> <span class="token operator">+</span> i<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">return</span> i <span class="token operator">></span> <span class="token number">50</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span><span class="token punctuation">)</span>
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<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><h4 id="串行和并行效率的比较"><a href="#串行和并行效率的比较" class="header-anchor">#</a> 串行和并行效率的比较</h4> <ul><li>使用for循环，串行Stream流，并行Stream流来对10亿个数字求和。看消耗的时间。</li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">StreamParallelTest</span> <span class="token punctuation">{</span>
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<span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> <span class="token constant">TIMES</span> <span class="token operator">=</span> <span class="token number">1000000000</span><span class="token punctuation">;</span>
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<span class="token keyword">long</span> start<span class="token punctuation">;</span>
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<span class="token annotation punctuation">@Before</span>
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<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">init</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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start <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token annotation punctuation">@Test</span>
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<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">useFor</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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<span class="token comment">// 消耗时间: 339ms</span>
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<span class="token keyword">int</span> sum <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
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<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> <span class="token constant">TIMES</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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sum <span class="token operator">+=</span> i<span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token annotation punctuation">@Test</span>
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<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">useSerialStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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<span class="token comment">// 获取足够长度的串行流进行加和</span>
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<span class="token comment">// 消耗时间: 631ms</span>
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<span class="token class-name">LongStream</span><span class="token punctuation">.</span><span class="token function">rangeClosed</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token constant">TIMES</span><span class="token punctuation">)</span>
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<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token class-name">Long</span><span class="token operator">::</span><span class="token function">sum</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token annotation punctuation">@Test</span>
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<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">useParallelStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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<span class="token comment">// 获取足够长度的并行流进行加和</span>
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<span class="token comment">// 消耗时间: 317ms</span>
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<span class="token class-name">LongStream</span><span class="token punctuation">.</span><span class="token function">rangeClosed</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token constant">TIMES</span><span class="token punctuation">)</span>
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<span class="token punctuation">.</span><span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
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<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token class-name">Long</span><span class="token operator">::</span><span class="token function">sum</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token punctuation">}</span>
|
||
|
||
<span class="token annotation punctuation">@After</span>
|
||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">destroy</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"消耗时间: "</span> <span class="token operator">+</span>
|
||
<span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> start<span class="token punctuation">)</span> <span class="token operator">+</span>
|
||
<span class="token string">"ms"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token punctuation">}</span>
|
||
<span class="token punctuation">}</span>
|
||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br></div></div><ul><li>我们可以看到parallelStream的效率是最高的。</li> <li>Stream并行处理的过程会分而治之，也就是将一个大任务切分成多个小任务，这表示每个任务都是一个操作。</li></ul> <h4 id="parallelstream线程安全问题"><a href="#parallelstream线程安全问题" class="header-anchor">#</a> ParallelStream线程安全问题</h4> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">StreamParallelTest</span> <span class="token punctuation">{</span>
|
||
<span class="token annotation punctuation">@Test</span>
|
||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">parallelStreamNotice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token number">1000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
|
||
<span class="token comment">// 并行线程不安全</span>
|
||
<span class="token comment">// list.size() = 947</span>
|
||
<span class="token class-name">IntStream</span><span class="token punctuation">.</span><span class="token function">range</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span>i <span class="token operator">-></span> list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"list.size() = "</span> <span class="token operator">+</span> list<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
|
||
<span class="token comment">// 解决线程安全问题方案一: 使用同步代码块</span>
|
||
<span class="token class-name">Object</span> lock <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Object</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">IntStream</span><span class="token punctuation">.</span><span class="token function">range</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span>i <span class="token operator">-></span> <span class="token punctuation">{</span>
|
||
<span class="token keyword">synchronized</span> <span class="token punctuation">(</span>lock<span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token punctuation">}</span>
|
||
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"list.size() = "</span> <span class="token operator">+</span> list<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
|
||
<span class="token comment">// 解决线程安全问题方案二: 使用线程安全的集合</span>
|
||
<span class="token comment">// 使用 Vector<Integer> 集合</span>
|
||
<span class="token class-name">Vector</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> v <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Vector</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">IntStream</span><span class="token punctuation">.</span><span class="token function">range</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span>i <span class="token operator">-></span> v<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"v.size() = "</span> <span class="token operator">+</span> v<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
|
||
<span class="token comment">// 解决线程安全问题方案二: 使用线程安全的集合</span>
|
||
<span class="token comment">// 使用集合工具类提供的线程安全的集合</span>
|
||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> synchronizedList <span class="token operator">=</span> <span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">synchronizedList</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">IntStream</span><span class="token punctuation">.</span><span class="token function">range</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span>i <span class="token operator">-></span> synchronizedList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"synchronizedList.size() = "</span> <span class="token operator">+</span> synchronizedList<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
|
||
<span class="token comment">// 解决线程安全问题方案三: 调用Stream流的collect/toArray</span>
|
||
<span class="token comment">// 使用Stream流的collect</span>
|
||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> collect <span class="token operator">=</span> <span class="token class-name">IntStream</span><span class="token punctuation">.</span><span class="token function">range</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">boxed</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"collect.size() = "</span> <span class="token operator">+</span> collect<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
|
||
<span class="token comment">// 解决线程安全问题方案三: 调用Stream流的collect/toArray</span>
|
||
<span class="token comment">// 使用Stream流的toArray</span>
|
||
<span class="token class-name">Integer</span><span class="token punctuation">[</span><span class="token punctuation">]</span> integers <span class="token operator">=</span> <span class="token class-name">IntStream</span><span class="token punctuation">.</span><span class="token function">range</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">parallel</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">boxed</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
<span class="token punctuation">.</span><span class="token function">toArray</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token operator">::</span><span class="token keyword">new</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"integers.length = "</span> <span class="token operator">+</span> integers<span class="token punctuation">.</span>length<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token punctuation">}</span>
|
||
<span class="token punctuation">}</span>
|
||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br></div></div><h3 id="_1-8-fork-join框架介绍"><a href="#_1-8-fork-join框架介绍" class="header-anchor">#</a> 1.8 Fork/Join框架介绍</h3> <ul><li>parallelStream使用的是Fork/Join框架。Fork/Join框架自JDK 7引入。Fork/Join框架可以将一个大任务拆分为很多小 任务来异步执行。 Fork/Join框架主要包含三个模块：
|
||
<ol><li>线程池：ForkJoinPool</li> <li>任务对象：ForkJoinTask</li> <li>执行任务的线程：ForkJoinWorkerThread</li></ol></li></ul> <p><img src="/java8/ForkJoin%E4%B8%80%E8%A7%88.png" alt=""></p> <h4 id="fork-join原理-分治法"><a href="#fork-join原理-分治法" class="header-anchor">#</a> Fork/Join原理-分治法</h4> <ul><li>ForkJoinPool主要用来使用分治法(Divide-and-Conquer Algorithm)来解决问题。典型的应用比如快速排序算法，ForkJoinPool需要使用相对少的线程来处理大量的任务。比如要对1000万个数据进行排序，那么会将这个任务分割成 两个500万的排序任务和一个针对这两组500万数据的合并任务。以此类推，对于500万的数据也会做出同样的分割处理，到最后会设置一个阈值来规定当数据规模到多少时，停止这样的分割处理。比如，当元素的数量小于10时，会停止分割，转而使用插入排序对它们进行排序。那么到最后，所有的任务加起来会有大概2000000+个。问题的关键在于，对于一个任务而言，只有当它所有的子任务完成之后，它才能够被执行。</li></ul> <p><img src="/java8/ForkJoin-%E5%88%86%E6%B2%BB%E6%B3%95.png" alt=""></p> <h4 id="fork-join原理-工作窃取算法"><a href="#fork-join原理-工作窃取算法" class="header-anchor">#</a> Fork/Join原理-工作窃取算法</h4> <ul><li>Fork/Join最核心的地方就是利用了现代硬件设备多核，在一个操作时候会有空闲的cpu，那么如何利用好这个空闲的cpu就成了提高性能的关键，而这里我们要提到的工作窃取（work-stealing）算法就是整个Fork/Join框架的核心理念 Fork/Join工作窃取（work-stealing）算法是指某个线程从其他队列里窃取任务来执行。</li></ul> <p><img src="/java8/ForkJoin-%E5%B7%A5%E4%BD%9C%E7%AA%83%E5%8F%96%E7%AE%97%E6%B3%95.png" alt=""></p> <ul><li><p>那么为什么需要使用工作窃取算法呢？假如我们需要做一个比较大的任务，我们可以把这个任务分割为若干互不依赖的子任务，为了减少线程间的竞争，于是把这些子任务分别放到不同的队列里，并为每个队列创建一个单独的线程来执行队列里的任务，线程和队列一一对应，比如A线程负责处理A队列里的任务。但是有的线程会先把自己队列里的 任务干完，而其他线程对应的队列里还有任务等待处理。干完活的线程与其等着，不如去帮其他线程干活，于是它就去其他线程的队列里窃取一个任务来执行。而在这时它们会访问同一个队列，所以为了减少窃取任务线程和被窃取任 务线程之间的竞争，通常会使用双端队列，被窃取任务线程永远从双端队列的头部拿任务执行，而窃取任务的线程永 远从双端队列的尾部拿任务执行。</p></li> <li><p>工作窃取算法的优点是充分利用线程进行并行计算，并减少了线程间的竞争，其缺点是在某些情况下还是存在竞争，比如双端队列里只有一个任务时。并且消耗了更多的系统资源，比如创建多个线程和多个双端队列。</p></li> <li><p>上文中已经提到了在Java 8引入了自动并行化的概念。它能够让一部分Java代码自动地以并行的方式执行，也就是我们使用了ForkJoinPool的ParallelStream。</p></li> <li><p>对于ForkJoinPool通用线程池的线程数量，通常使用默认值就可以了，即运行时计算机的处理器数量。可以通过设置系统属性：<code>java.util.concurrent.ForkJoinPool.common.parallelism=N</code>（N为线程数量），来调整ForkJoinPool的线程数量，可以尝试调整成不同的参数来观察每次的输出结果。</p></li></ul> <h4 id="fork-join案例"><a href="#fork-join案例" class="header-anchor">#</a> Fork/Join案例</h4> <ul><li>需求：使用Fork/Join计算1-10000的和，当一个任务的计算数量大于3000时拆分任务，数量小于3000时计算。</li></ul> <p><img src="/java8/ForkJoin%E6%A1%88%E4%BE%8B.png" alt=""></p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">ForkJoinDemo</span> <span class="token punctuation">{</span>
|
||
|
||
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
<span class="token keyword">long</span> start <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">ForkJoinPool</span> pool <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ForkJoinPool</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">SumRecursiveTask</span> task <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">SumRecursiveTask</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">10000L</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">Long</span> result <span class="token operator">=</span> pool<span class="token punctuation">.</span><span class="token function">invoke</span><span class="token punctuation">(</span>task<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"result = "</span> <span class="token operator">+</span> result<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token keyword">long</span> end <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
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|
||
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"消耗的时间为: "</span> <span class="token operator">+</span> <span class="token punctuation">(</span>end <span class="token operator">-</span> start<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
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<span class="token punctuation">}</span>
|
||
|
||
<span class="token punctuation">}</span>
|
||
|
||
<span class="token keyword">class</span> <span class="token class-name">SumRecursiveTask</span> <span class="token keyword">extends</span> <span class="token class-name">RecursiveTask</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Long</span><span class="token punctuation">></span></span> <span class="token punctuation">{</span>
|
||
|
||
<span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">long</span> <span class="token constant">THRESHOLD</span> <span class="token operator">=</span> <span class="token number">3000L</span><span class="token punctuation">;</span>
|
||
<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">long</span> start<span class="token punctuation">;</span>
|
||
<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">long</span> end<span class="token punctuation">;</span>
|
||
|
||
<span class="token keyword">public</span> <span class="token class-name">SumRecursiveTask</span><span class="token punctuation">(</span><span class="token keyword">long</span> start<span class="token punctuation">,</span> <span class="token keyword">long</span> end<span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
<span class="token keyword">this</span><span class="token punctuation">.</span>start <span class="token operator">=</span> start<span class="token punctuation">;</span>
|
||
<span class="token keyword">this</span><span class="token punctuation">.</span>end <span class="token operator">=</span> end<span class="token punctuation">;</span>
|
||
<span class="token punctuation">}</span>
|
||
|
||
<span class="token annotation punctuation">@Override</span>
|
||
<span class="token keyword">protected</span> <span class="token class-name">Long</span> <span class="token function">compute</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
<span class="token keyword">long</span> length <span class="token operator">=</span> end <span class="token operator">-</span> start<span class="token punctuation">;</span>
|
||
|
||
<span class="token keyword">if</span> <span class="token punctuation">(</span>length <span class="token operator"><=</span> <span class="token constant">THRESHOLD</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
<span class="token comment">// 任务不用再拆分了.可以计算了</span>
|
||
<span class="token keyword">long</span> sum <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
|
||
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">long</span> i <span class="token operator">=</span> start<span class="token punctuation">;</span> i <span class="token operator"><=</span> end<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
sum <span class="token operator">+=</span> i<span class="token punctuation">;</span>
|
||
<span class="token punctuation">}</span>
|
||
<span class="token keyword">return</span> sum<span class="token punctuation">;</span>
|
||
<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
|
||
<span class="token comment">// 数量大于预定的数量,任务还需要再拆分</span>
|
||
<span class="token keyword">long</span> middle <span class="token operator">=</span> <span class="token punctuation">(</span>start <span class="token operator">+</span> end<span class="token punctuation">)</span> <span class="token operator">/</span> <span class="token number">2</span><span class="token punctuation">;</span>
|
||
|
||
<span class="token class-name">SumRecursiveTask</span> left <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">SumRecursiveTask</span><span class="token punctuation">(</span>start<span class="token punctuation">,</span> middle<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
left<span class="token punctuation">.</span><span class="token function">fork</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token class-name">SumRecursiveTask</span> right <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">SumRecursiveTask</span><span class="token punctuation">(</span>middle <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">,</span> end<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
right<span class="token punctuation">.</span><span class="token function">fork</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token keyword">return</span> left<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> right<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
<span class="token punctuation">}</span>
|
||
<span class="token punctuation">}</span>
|
||
<span class="token punctuation">}</span>
|
||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br></div></div><h3 id="_1-9-小结"><a href="#_1-9-小结" class="header-anchor">#</a> 1.9 小结</h3> <ol><li>parallelStream是线程不安全的</li> <li>parallelStream适用的场景是CPU密集型的，只是做到别浪费CPU，假如本身电脑CPU的负载很大，那还到处用并行流，那并不能起到作用</li> <li>I/O密集型磁盘I/O、网络I/O都属于I/O操作，这部分操作是较少消耗CPU资源，一般并行流中不适用于I/O密集型的操作，就比如使用并流行进行大批量的消息推送，涉及到了大量I/O，使用并行流反而慢了很多</li> <li>在使用并行流的时候是无法保证元素的顺序的，也就是即使你用了同步集合也只能保证元素都正确但无法保证其中的顺序</li></ol></div></section> <footer class="page-edit"><!----> <!----></footer> <div class="page-nav"><p class="inner"><span class="prev"><a href="/blogs/java/java8/java8-2.html" class="prev">
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</a></span></p></div> <div class="comments-wrapper"><!----></div></main></div> <!----></div> <ul class="sub-sidebar sub-sidebar-wrapper" style="width:12rem;" data-v-b57cc07c data-v-7dd95ae2><li class="level-2" data-v-b57cc07c><a href="/blogs/java/java8/java8-3.html#_1-stream流-续" class="sidebar-link reco-side-_1-stream流-续" data-v-b57cc07c>1 Stream流-续</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-3.html#_1-7-并行的stream流" class="sidebar-link reco-side-_1-7-并行的stream流" data-v-b57cc07c>1.7 并行的Stream流</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-3.html#_1-8-fork-join框架介绍" class="sidebar-link reco-side-_1-8-fork-join框架介绍" data-v-b57cc07c>1.8 Fork/Join框架介绍</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-3.html#_1-9-小结" class="sidebar-link reco-side-_1-9-小结" data-v-b57cc07c>1.9 小结</a></li></ul></div></div></div><div class="global-ui"><div class="back-to-ceiling" style="right:1rem;bottom:6rem;width:2.5rem;height:2.5rem;border-radius:.25rem;line-height:2.5rem;display:none;" data-v-c6073ba8 data-v-c6073ba8><svg t="1574745035067" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5404" class="icon" data-v-c6073ba8><path d="M526.60727968 10.90185116a27.675 27.675 0 0 0-29.21455937 0c-131.36607665 82.28402758-218.69155461 228.01873535-218.69155402 394.07834331a462.20625001 462.20625001 0 0 0 5.36959153 69.94390903c1.00431239 6.55289093-0.34802892 13.13561351-3.76865779 18.80351572-32.63518765 54.11355614-51.75690182 118.55860487-51.7569018 187.94566865a371.06718723 371.06718723 0 0 0 11.50484808 91.98906777c6.53300375 25.50556257 41.68394495 28.14064038 52.69160883 4.22606766 17.37162448-37.73630017 42.14135425-72.50938081 72.80769204-103.21549295 2.18761121 3.04276886 4.15646224 6.24463696 6.40373557 9.22774369a1871.4375 1871.4375 0 0 0 140.04691725 5.34970492 1866.36093723 1866.36093723 0 0 0 140.04691723-5.34970492c2.24727335-2.98310674 4.21612437-6.18497483 6.3937923-9.2178004 30.66633723 30.70611158 55.4360664 65.4791928 72.80769147 103.21549355 11.00766384 23.91457269 46.15860503 21.27949489 52.69160879-4.22606768a371.15156223 371.15156223 0 0 0 11.514792-91.99901164c0-69.36717486-19.13165746-133.82216804-51.75690182-187.92578088-3.42062944-5.66790279-4.76302748-12.26056868-3.76865837-18.80351632a462.20625001 462.20625001 0 0 0 5.36959269-69.943909c-0.00994388-166.08943902-87.32547796-311.81420293-218.6915546-394.09823051zM605.93803103 357.87693858a93.93749974 93.93749974 0 1 1-187.89594924 6.1e-7 93.93749974 93.93749974 0 0 1 187.89594924-6.1e-7z" p-id="5405" data-v-c6073ba8></path><path d="M429.50777625 765.63860547C429.50777625 803.39355007 466.44236686 1000.39046097 512.00932183 1000.39046097c45.56695499 0 82.4922232-197.00623328 82.5015456-234.7518555 0-37.75494459-36.9345906-68.35043303-82.4922232-68.34111062-45.57627738-0.00932239-82.52019037 30.59548842-82.51086798 68.34111062z" p-id="5406" data-v-c6073ba8></path></svg></div></div></div>
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