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zhuhjay 22e48d9558 build(www): 添加 Drone CI 流水线配置 
- 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
2025-11-01 13:36:00 +08:00

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"),a("p",[s._v("使用命令 "),a("code",[s._v("jvisualvm")]),s._v(" 打开可视化界面，选择当前执行的进程，查看详细信息，然后进行堆内存 dump")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1669044220427.png",alt:"1669044220427"}})]),s._v(" "),a("p",[s._v("可以发现当前的 ArrayList 对象占用的内存高达约 200M 左右的内存，点击进去查看该对象的详细信息")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1669044331372.png",alt:"1669044331372"}})]),s._v(" "),a("p",[s._v("在 ArrayList 对象中的每一个元素都占用了约 1M 的内存大小，一共有200个元素，则总占用就有了大约 200M 的堆内存空间，由此快速定位到代码中存在的问题")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1669044475571.png",alt:"1669044475571"}})])])])])]),s._v(" "),a("h2",{attrs:{id:"_5-方法区"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_5-方法区"}},[s._v("#")]),s._v(" 5 方法区")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1669044952813.png",alt:"1669044952813"}})]),s._v(" "),a("h3",{attrs:{id:"_5-1-定义"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_5-1-定义"}},[s._v("#")]),s._v(" 5.1 定义")]),s._v(" 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虚拟机抛出一个。"),a("code",[s._v("OutOfMemoryError")])])])]),s._v(" "),a("h3",{attrs:{id:"_5-2-组成"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_5-2-组成"}},[s._v("#")]),s._v(" 5.2 组成")]),s._v(" "),a("p",[s._v("JDK6 和 JDK8 的内存结构发生了变化")]),s._v(" "),a("blockquote",[a("p",[a("strong",[s._v("注意")]),s._v("：图中的 常量池 指的是 运行时常量池")])]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1669045525089.png",alt:"1669045525089"}})]),s._v(" "),a("h3",{attrs:{id:"_5-3-方法区内存溢出"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_5-3-方法区内存溢出"}},[s._v("#")]),s._v(" 5.3 方法区内存溢出")]),s._v(" "),a("ul",[a("li",[s._v("JDK1.8 以前会导致永久代内存溢出："),a("code",[s._v("java.lang.OutOfMemoryError: PermGen space")])]),s._v(" "),a("li",[s._v("JDK1.8 以后会导致元空间内存溢出："),a("code",[s._v("java.lang.OutOfMemoryError: Metaspace")])])]),s._v(" "),a("p",[s._v("演示 JDK1.8 以后元空间内存溢出（JDK1.6 代码几乎相同，永久代使用 "),a("code",[s._v("-XX:MaxPermSize=8m")]),s._v("）")]),s._v(" "),a("div",{staticClass:"language-java 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"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 版本号，public，类名，包名，父类，接口")]),s._v("\n cw"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("visit")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Opcodes")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("V1_8")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Opcodes")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("ACC_PUBLIC")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"Class"')]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" 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punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("toByteArray")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 执行类的加载")]),s._v("\n test"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("defineClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"Class"')]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" code"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token 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punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br")])]),a("p",[s._v("在 1.8 以后元空间使用的是系统没存，没有限制大小，不会发生溢出的情况，需要设置 "),a("code",[s._v("-XX:MaxMetaspaceSize=8m")])]),s._v(" "),a("div",{staticClass:"language-tex line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-tex"}},[a("code",[s._v('5411\nException in thread "main" java.lang.OutOfMemoryError: Metaspace\n\tat java.lang.ClassLoader.defineClass1(Native Method)\n\tat java.lang.ClassLoader.defineClass(ClassLoader.java:763)\n\tat java.lang.ClassLoader.defineClass(ClassLoader.java:642)\n\tat com.zhuhjay.Demo1_7.main(Demo1_7.java:23)\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br")])]),a("p",[s._v("方法区内存溢出场景：")]),s._v(" "),a("ul",[a("li",[s._v("Spring")]),s._v(" "),a("li",[s._v("Mybatis")])]),s._v(" "),a("p",[s._v("这些场景都会使用 CGLIB 等代理技术动态的生成字节码，使用不当可能会导致方法区内存溢出的情况。")]),s._v(" "),a("h3",{attrs:{id:"_5-4-运行时常量池"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_5-4-运行时常量池"}},[s._v("#")]),s._v(" 5.4 运行时常量池")]),s._v(" "),a("ul",[a("li",[s._v("常量池，就是一张表，虚拟机指令根据这张常量表找到要执行的类名、方法名、参数类型、字面量等信息")]),s._v(" "),a("li",[s._v("运行时常量池，常量池是 *.class 文件中的，当该类被加载，它的常量池信息就会放入运行时常量池，并把里面的符号地址变为真实地址")])]),s._v(" "),a("blockquote",[a("p",[a("strong",[s._v("Tip")]),s._v(": 常量池的概念解析")]),s._v(" "),a("p",[s._v("编译运行以下代码")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo1_8")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"hello world"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br")])]),a("p",[s._v("将编译后的 class 文件进行反编译 "),a("code",[s._v("javap -v Demo1_8.class")])]),s._v(" "),a("ul",[a("li",[s._v("源码 1-8 行是文件的 类的基本信息")]),s._v(" "),a("li",[s._v("源码 9-42 行是 常量池信息")]),s._v(" "),a("li",[s._v("源码 44-72 行是 类方法定义信息")]),s._v(" "),a("li",[a("strong",[s._v("当 class 文件被运行之后，所有的 "),a("code",[s._v("#..")]),s._v(" 都会被赋予真实的物理地址信息")])])]),s._v(" "),a("div",{staticClass:"language-tex line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-tex"}},[a("code",[s._v('Classfile /G:/Idea_workspace/JVM/target/classes/com/zhuhjay/Demo1_8.class\n Last modified 2022-11-22; size 548 bytes\n MD5 checksum 551e83a2ede53badac918978a8846964\n Compiled from "Demo1_8.java"\npublic class com.zhuhjay.Demo1_8\n minor version: 0\n major version: 52\n flags: ACC_PUBLIC, ACC_SUPER\nConstant pool:\n #1 = Methodref #6.#20 // java/lang/Object."<init>":()V\n #2 = Fieldref #21.#22 // java/lang/System.out:Ljava/io/PrintStream;\n #3 = String #23 // hello world\n #4 = Methodref #24.#25 // java/io/PrintStream.println:(Ljava/lang/String;)V\n #5 = Class #26 // com/zhuhjay/Demo1_8\n #6 = Class #27 // java/lang/Object\n #7 = Utf8 <init>\n #8 = Utf8 ()V\n #9 = Utf8 Code\n #10 = Utf8 LineNumberTable\n #11 = Utf8 LocalVariableTable\n #12 = Utf8 this\n #13 = Utf8 Lcom/zhuhjay/Demo1_8;\n #14 = Utf8 main\n #15 = Utf8 ('),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("Ljava/lang/String;)V\n #16 = Utf8 args\n #17 = Utf8 "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v('Ljava/lang/String;\n #18 = Utf8 SourceFile\n #19 = Utf8 Demo1_8.java\n #20 = NameAndType #7:#8 // "<init>":()V\n #21 = Class #28 // java/lang/System\n #22 = NameAndType #29:#30 // out:Ljava/io/PrintStream;\n #23 = Utf8 hello world\n #24 = Class #31 // java/io/PrintStream\n #25 = NameAndType #32:#33 // println:(Ljava/lang/String;)V\n #26 = Utf8 com/zhuhjay/Demo1_8\n #27 = Utf8 java/lang/Object\n #28 = Utf8 java/lang/System\n #29 = Utf8 out\n #30 = Utf8 Ljava/io/PrintStream;\n #31 = Utf8 java/io/PrintStream\n #32 = Utf8 println\n #33 = Utf8 (Ljava/lang/String;)V\n'),a("span",{pre:!0,attrs:{class:"token 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"),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br")])]),a("p",[a("strong",[s._v("JDK1.8 验证")]),s._v("：需要设置堆内存的大小 "),a("code",[s._v("-Xmx10m")]),s._v("，会发现有以下结果，报错信息和预想的结果不一样？")]),s._v(" "),a("ul",[a("li",[s._v("原来，在 JVM规范中 当GC垃圾回收花了 98% 的时间只释放了 2% 的堆空间时，JVM 就会认为该程序没救了，就直接抛出该异常")]),s._v(" "),a("li",[s._v("那么要跳过这个限制，需要再多配置一个参数 "),a("code",[s._v("-XX:-UseGCOverheadLimit")])])]),s._v(" "),a("div",{staticClass:"language-tex line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-tex"}},[a("code",[s._v("java.lang.OutOfMemoryError: GC overhead limit exceeded\n\tat java.lang.Integer.toString(Integer.java:403)\n\tat java.lang.String.valueOf(String.java:3099)\n\tat com.zhuhjay.Demo1_10.main(Demo1_10.java:16)\n145367\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br")])]),a("p",[s._v("最终结果就是预想的结果了！")]),s._v(" "),a("div",{staticClass:"language-tex line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-tex"}},[a("code",[s._v('*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message can\'t create byte arrau at JPLISAgent.c line: 813\njava.lang.OutOfMemoryError: Java heap space\n\tat java.lang.Integer.toString(Integer.java:401)\n\tat java.lang.String.valueOf(String.java:3099)\n\tat com.zhuhjay.Demo1_10.main(Demo1_10.java:16)\n146837\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br")])]),a("p",[a("strong",[s._v("JDK1.6 验证")]),s._v("：需要设置永久代内存的大小 "),a("code",[s._v("-XX:MaxPermSize=10m")])]),s._v(" "),a("h4",{attrs:{id:"_5-8-stringtable-垃圾回收"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_5-8-stringtable-垃圾回收"}},[s._v("#")]),s._v(" 5.8 StringTable 垃圾回收")]),s._v(" "),a("p",[s._v("查看字符串常量池 StringTable 的垃圾回收是否会在空间不足时进行字符串常量池的垃圾回收")]),s._v(" "),a("p",[s._v("示例代码，为了更进一步查看堆内存和字符串常量池的空间，需要添加以下参数")]),s._v(" "),a("ul",[a("li",[a("code",[s._v("-Xmx10m")]),s._v("：设置堆的大小，为了方便测试GC垃圾回收")]),s._v(" "),a("li",[a("code",[s._v("-XX:+PrintStringTableStatistics")]),s._v("：打印字符串表的信息")]),s._v(" "),a("li",[a("code",[s._v("-XX:+PrintGCDetails -verbose:gc")]),s._v("：统计垃圾回收的信息")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo1_11")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n\t\t\t"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// TODO 待插入代码")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Throwable")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("printStackTrace")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("finally")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("p",[s._v("查看输出结果，认识一下下面所代表的含义")]),s._v(" "),a("div",{staticClass:"language-tex line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-tex"}},[a("code",[s._v("Heap\t\t# 堆内存的占用情况\n PSYoungGen total 2560K, used 1676K "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("0x00000000ffd00000, 0x0000000100000000, 0x0000000100000000)\n eden space 2048K, 81"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("% used [0x00000000ffd00000,0x00000000ffea3198,0x00000000fff00000)")]),s._v("\n from space 512K, 0"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("% used [0x00000000fff80000,0x00000000fff80000,0x0000000100000000)")]),s._v("\n to space 512K, 0"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("% used [0x00000000fff00000,0x00000000fff00000,0x00000000fff80000)")]),s._v("\n ParOldGen total 7168K, used 0K "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("0x00000000ff600000, 0x00000000ffd00000, 0x00000000ffd00000)\n object space 7168K, 0"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("% used [0x00000000ff600000,0x00000000ff600000,0x00000000ffd00000)")]),s._v("\n Metaspace used 3167K, capacity 4496K, committed 4864K, reserved 1056768K\n class space used 345K, capacity 388K, committed 512K, reserved 1048576K\nSymbolTable statistics:\t\t# 符号表的详细信息（也是常量池的一部分，但是并不关心这部分内容）\nNumber of buckets : 20011 = 160088 bytes, avg 8.000\nNumber of entries : 13260 = 318240 bytes, avg 24.000\nNumber of literals : 13260 = 568232 bytes, avg 42.853\nTotal footprint : = 1046560 bytes\nAverage bucket size : 0.663\nVariance of bucket size : 0.666\nStd. dev. of bucket size: 0.816\nMaximum bucket size : 6\nStringTable statistics:\t\t# StringTable 统计信息，使用 hashtable 结构\nNumber of buckets : 60013 = 480104 bytes, avg 8.000\t# 桶个数 = 字节数\nNumber of entries : 1739 = 41736 bytes, avg 24.000\t# 键值对个数 = 字节数\nNumber of literals : 1739 = 156592 bytes, avg 90.047\t# 字符串常量个数 = 字节数\nTotal footprint : = 678432 bytes\t\t\t\t# 总的空间\nAverage bucket size : 0.029\nVariance of bucket size : 0.029\nStd. dev. of bucket size: 0.171\nMaximum bucket size : 3\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br")])]),a("p",[s._v("现在在以上代码中插入以下代码：将10000个字符串添加到字符串常量池中，此时字符串常量池中理应会在原来的 1739 基础上多 10000")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" j "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" j "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10000")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" j"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("valueOf")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("j"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("intern")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n i"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br")])]),a("p",[s._v("可以看到此时运行就有了 GC垃圾回收 的信息，此时字符串常量池没有达到预期的效果，说明当常量池中有不被使用的数据会被垃圾回收")]),s._v(" "),a("div",{staticClass:"language-tex line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-tex"}},[a("code",[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("GC (Allocation Failure) "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("PSYoungGen: 2048K->488K(2560K)"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" 2048K->704K(9728K), 0.0031150 secs"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("Times: user=0.00 sys=0.00, real=0.00 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1.7G 时就溢出了")]),s._v(" "),a("div",{staticClass:"language-tex line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-tex"}},[a("code",[s._v('17\nException in thread "main" java.lang.OutOfMemoryError: Direct buffer memory\n\tat java.nio.Bits.reserveMemory(Bits.java:695)\n\tat java.nio.DirectByteBuffer.<init>(DirectByteBuffer.java:123)\n\tat java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:311)\n\tat com.zhuhjay.Demo1_13.main(Demo1_13.java:19)\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br")])]),a("h4",{attrs:{id:"_6-2-3-直接内存释放"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_6-2-3-直接内存释放"}},[s._v("#")]),s._v(" 6.2.3 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