查看Java字节码

1 javac –verbose查看运行类是加载了那些jar文件

HelloWorld演示：

public class Test {

    public static void main(String[] args) {

        Object lock = new Object();

        synchronized (lock) {

            System.out.println("hello world.");

        }

    }

}

javac –verbose HelloWorld.java

D:\shiva\omcs\Test\src\sync>javac -verbose Test.java

[解析开始时间 RegularFileObject[Test.java]]

[解析已完成, 用时  毫秒]

[源文件的搜索路径: .,C:\Java\jdk1..0_31\lib,C:\Java\jdk1..0_31\lib\tools.jar]

[类文件的搜索路径: C:\Java\jdk1..0_31\jre\lib\resources.jar,C:\Java\jdk1..0_31\jre\lib\rt.jar,C:\Java\jdk1..0_31\jre

lib\sunrsasign.jar,C:\Java\jdk1..0_31\jre\lib\jsse.jar,C:\Java\jdk1..0_31\jre\lib\jce.jar,C:\Java\jdk1..0_31\jre\lib

charsets.jar,C:\Java\jdk1..0_31\jre\lib\jfr.jar,C:\Java\jdk1..0_31\jre\classes,C:\Java\jdk1..0_31\jre\lib\ext\access

bridge-.jar,C:\Java\jdk1..0_31\jre\lib\ext\cldrdata.jar,C:\Java\jdk1..0_31\jre\lib\ext\dnsns.jar,C:\Java\jdk1..0_3

\jre\lib\ext\jaccess.jar,C:\Java\jdk1..0_31\jre\lib\ext\jfxrt.jar,C:\Java\jdk1..0_31\jre\lib\ext\localedata.jar,C:\Ja

a\jdk1..0_31\jre\lib\ext\nashorn.jar,C:\Java\jdk1..0_31\jre\lib\ext\sunec.jar,C:\Java\jdk1..0_31\jre\lib\ext\sunjce_

rovider.jar,C:\Java\jdk1..0_31\jre\lib\ext\sunmscapi.jar,C:\Java\jdk1..0_31\jre\lib\ext\sunpkcs11.jar,C:\Java\jdk1..

_31\jre\lib\ext\zipfs.jar,.,C:\Java\jdk1..0_31\lib,C:\Java\jdk1..0_31\lib\tools.jar]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Object.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/String.class)]]

[正在检查sync.Test]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/io/Serializable.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/AutoCloseable.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Byte.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Character.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Short.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Long.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Float.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Integer.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Double.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Boolean.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Void.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/System.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/io/PrintStream.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/io/FilterOutputStream.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/io/OutputStream.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Comparable.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/CharSequence.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Appendable.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/io/Closeable.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/io/Flushable.class)]]

[正在加载ZipFileIndexFileObject[C:\Java\jdk1..0_31\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Throwable.class)]]

[已写入RegularFileObject[Test.class]]

[共  毫秒]

D:\shiva\omcs\Test\src\sync>

可以看到虚拟机编译时做了那些事情……

java -verbose Test

可以看到虚拟机运行一个程序时加载的jar包

更多内容查看javac –help命令

2  javap查看字节码

首先使用javap –help可以查看到各种命令，各个命令什么作用，可以自己运行试试……

这里只是测试 javap –c和javap –verbose

javap –c HelloWorld

D:\shiva\omcs\Test\bin\sync>javap -c Test

警告: 二进制文件Test包含sync.Test

Compiled from "Test.java"

public class sync.Test {

  public sync.Test();

    Code:

       : aload_0

       : invokespecial #                  // Method java/lang/Object."<init>":()V

       : return

  public static void main(java.lang.String[]);

    Code:

       : new           #                  // class java/lang/Object

       : dup

       : invokespecial #                  // Method java/lang/Object."<init>":()V

       : astore_1

       : aload_1

       : dup

      : astore_2

      : monitorenter

      : getstatic     #                 // Field java/lang/System.out:Ljava/io/PrintStream;

      : ldc           #                 // String hello world.

      : invokevirtual #                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

      : aload_2

      : monitorexit

      : goto

      : aload_2

      : monitorexit

      : athrow

      : return

    Exception table:

       from    to  target type

                     any

                     any

}

D:\shiva\omcs\Test\bin\sync>cd ..

可以查看字节码，从中可以得到各种变量的信息等等

但是javap –verbose可以看到更加清楚的信息。如下图

D:\shiva\omcs\Test\bin\sync>javap -verbose Test

警告: 二进制文件Test包含sync.Test

Classfile /D:/shiva/omcs/Test/bin/sync/Test.class

  Last modified --; size  bytes

  MD5 checksum 954bd4bcfcff2732e5be9925e518e79a

  Compiled from "Test.java"

public class sync.Test

  minor version:

  major version:

  flags: ACC_PUBLIC, ACC_SUPER

Constant pool:

   # = Class              #             // sync/Test

   # = Utf8               sync/Test

   # = Class              #             // java/lang/Object

   # = Utf8               java/lang/Object

   # = Utf8               <init>

   # = Utf8               ()V

   # = Utf8               Code

   # = Methodref          #.#          // java/lang/Object."<init>":()V

   # = NameAndType        #:#          // "<init>":()V

  # = Utf8               LineNumberTable

  # = Utf8               LocalVariableTable

  # = Utf8               this

  # = Utf8               Lsync/Test;

  # = Utf8               main

  # = Utf8               ([Ljava/lang/String;)V

  # = Fieldref           #.#        // java/lang/System.out:Ljava/io/PrintStream;

  # = Class              #            // java/lang/System

  # = Utf8               java/lang/System

  # = NameAndType        #:#        // out:Ljava/io/PrintStream;

  # = Utf8               out

  # = Utf8               Ljava/io/PrintStream;

  # = String             #            // hello world.

  # = Utf8               hello world.

  # = Methodref          #.#        // java/io/PrintStream.println:(Ljava/lang/String;)V

  # = Class              #            // java/io/PrintStream

  # = Utf8               java/io/PrintStream

  # = NameAndType        #:#        // println:(Ljava/lang/String;)V

  # = Utf8               println

  # = Utf8               (Ljava/lang/String;)V

  # = Utf8               args

  # = Utf8               [Ljava/lang/String;

  # = Utf8               lock

  # = Utf8               Ljava/lang/Object;

  # = Utf8               StackMapTable

  # = Class              #            // "[Ljava/lang/String;"

  # = Class              #            // java/lang/Throwable

  # = Utf8               java/lang/Throwable

  # = Utf8               SourceFile

  # = Utf8               Test.java

{

  public sync.Test();

    descriptor: ()V

    flags: ACC_PUBLIC

    Code:

      stack=, locals=, args_size=

         : aload_0

         : invokespecial #                  // Method java/lang/Object."<init>":()V

         : return

      LineNumberTable:

        line :

      LocalVariableTable:

        Start  Length  Slot  Name   Signature

                          this   Lsync/Test;

  public static void main(java.lang.String[]);

    descriptor: ([Ljava/lang/String;)V

    flags: ACC_PUBLIC, ACC_STATIC

    Code:

      stack=, locals=, args_size=

         : new           #                  // class java/lang/Object

         : dup

         : invokespecial #                  // Method java/lang/Object."<init>":()V

         : astore_1

         : aload_1

         : dup

        : astore_2

        : monitorenter

        : getstatic     #                 // Field java/lang/System.out:Ljava/io/PrintStream;

        : ldc           #                 // String hello world.

        : invokevirtual #                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

        : aload_2

        : monitorexit

        : goto

        : aload_2

        : monitorexit

        : athrow

        : return

      Exception table:

         from    to  target type

                       any

                       any

      LineNumberTable:

        line :

        line :

        line :

        line :

        line :

      LocalVariableTable:

        Start  Length  Slot  Name   Signature

                         args   [Ljava/lang/String;

                         lock   Ljava/lang/Object;

      StackMapTable: number_of_entries =

        frame_type =  /* full_frame */

          offset_delta =

          locals = [ class "[Ljava/lang/String;", class java/lang/Object, class java/lang/Object ]

          stack = [ class java/lang/Throwable ]

        frame_type =  /* chop */

          offset_delta =

}

SourceFile: "Test.java"

D:\shiva\omcs\Test\bin\sync>

以上为命令查看java字节码文件过程，对了解java背后的秘密，深层次理解java有用

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