目录

1、在IDEA利用断点进行debug模式，观察栈帧的入栈出栈

2、在IDEA中使用javap指令对class文件进行解析

3、在IDEA中利用jclasslib插件解析.class文件

在IDEA中输入这样的代码

import java.util.function.DoubleToIntFunction;

/*

(1)现在设置的代码补全是alt+/

(2)快速注释是command+/

(3)快速格式化代码 alt+command+L

(4)利用断点进入debug模式，观察栈的栈帧和局部变量表，进栈出栈操作

进入都out/production/learnJVMdemo文件夹下，有一个当前类的.class文件，对它进行反编译

在Terminal界面下输入反编译指令：javap -v StackFrameTest.class,观察反编译的输出结果

*/

public class TestStackFrame {

public static void main(String[] args) {

System.out.println("这是main即将执行");

TestStackFrame tt = new TestStackFrame();

try {

tt.method1();

}catch (Exception e){

e.printStackTrace();

}

tt.method1();

System.out.println();

System.out.println("这是main执行完毕");

}

public void method1(){

System.out.println("这是method1即将执行");

int I=10;

int j=11;

method2();

//System.out.println(10/0); //这个会报出一个错误

System.out.println("这是method1执行完毕");

}

public void method2(){

System.out.println("这是method2即将执行");

int I=10;

int j=11;

method3();

System.out.println("这是method2执行完毕");

}

public void method3(){

System.out.println("这是method3即将执行");

int I=10;

int j=11;

System.out.println("这是method3执行完毕");

}

}

1、在IDEA利用断点进行debug模式，观察栈帧的入栈出栈

在代码某处加入红色断点

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右键，进入debug模式

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在下方可以观察debug窗口

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点击箭头朝下的蓝色按钮，执行下一条语句

image.png

2、在IDEA中使用javap指令对class文件进行解析

对上面这段代码进行complie后，会生成.class文件，生成的.class文件在out/production文件夹下，其中learnJVMdemo是你创建的IDEA项目的名称。

image.png

在IDEA的Terminal输入指令

image.png

然后输入反编译指令，对class文件进行反编译

image.png

反编译输入的结果是(仔细分析反编译的结果，能看到学习jvm途中遇见的很多老朋友，例如常量池、局部变量表、方法等)：

a1234@MacBook-Pro learnJVMdemo % javap -v TestStackFrame.class

Classfile /Users/a1234/IDEA_project/learnJVMdemo/out/production/learnJVMdemo/TestStackFrame.class

Last modified 2020年5月21日; size 1446 bytes

SHA-256 checksum 5c1b47cc1ffe73348dbbc7c2713bff73502254e51e2e528f33c84315f11f2f17

Compiled from "TestStackFrame.java"

public class TestStackFrame

minor version: 0

major version: 58

flags: (0x0021) ACC_PUBLIC, ACC_SUPER

this_class: #21 // TestStackFrame

super_class: #2 // java/lang/Object

interfaces: 0, fields: 0, methods: 5, attributes: 1

Constant pool:

#1 = Methodref #2.#3 // java/lang/Object."":()V

#2 = Class #4 // java/lang/Object

#3 = NameAndType #5:#6 // "":()V

#4 = Utf8 java/lang/Object

#5 = Utf8

#6 = Utf8 ()V

#7 = Fieldref #8.#9 // java/lang/System.out:Ljava/io/PrintStream;

#8 = Class #10 // java/lang/System

#9 = NameAndType #11:#12 // out:Ljava/io/PrintStream;

#10 = Utf8 java/lang/System

#11 = Utf8 out

#12 = Utf8 Ljava/io/PrintStream;

#13 = String #14 // 这是main即将执行

#14 = Utf8 这是main即将执行

#15 = Methodref #16.#17 // java/io/PrintStream.println:(Ljava/lang/String;)V

#16 = Class #18 // java/io/PrintStream

#17 = NameAndType #19:#20 // println:(Ljava/lang/String;)V

#18 = Utf8 java/io/PrintStream

#19 = Utf8 println

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

#21 = Class #22 // TestStackFrame

#22 = Utf8 TestStackFrame

#23 = Methodref #21.#3 // TestStackFrame."":()V

#24 = Methodref #21.#25 // TestStackFrame.method1:()V

#25 = NameAndType #26:#6 // method1:()V

#26 = Utf8 method1

#27 = Class #28 // java/lang/Exception

#28 = Utf8 java/lang/Exception

#29 = Methodref #27.#30 // java/lang/Exception.printStackTrace:()V

#30 = NameAndType #31:#6 // printStackTrace:()V

#31 = Utf8 printStackTrace

#32 = Methodref #16.#33 // java/io/PrintStream.println:()V

#33 = NameAndType #19:#6 // println:()V

#34 = String #35 // 这是main执行完毕

#35 = Utf8 这是main执行完毕

#36 = String #37 // 这是method1即将执行

#37 = Utf8 这是method1即将执行

#38 = Methodref #21.#39 // TestStackFrame.method2:()V

#39 = NameAndType #40:#6 // method2:()V

#40 = Utf8 method2

#41 = String #42 // 这是method1执行完毕

#42 = Utf8 这是method1执行完毕

#43 = String #44 // 这是method2即将执行

#44 = Utf8 这是method2即将执行

#45 = Methodref #21.#46 // TestStackFrame.method3:()V

#46 = NameAndType #47:#6 // method3:()V

#47 = Utf8 method3

#48 = String #49 // 这是method2执行完毕

#49 = Utf8 这是method2执行完毕

#50 = String #51 // 这是method3即将执行

#51 = Utf8 这是method3即将执行

#52 = String #53 // 这是method3执行完毕

#53 = Utf8 这是method3执行完毕

#54 = Utf8 Code

#55 = Utf8 LineNumberTable

#56 = Utf8 LocalVariableTable

#57 = Utf8 this

#58 = Utf8 LTestStackFrame;

#59 = Utf8 main

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

#61 = Utf8 e

#62 = Utf8 Ljava/lang/Exception;

#63 = Utf8 args

#64 = Utf8 [Ljava/lang/String;

#65 = Utf8 tt

#66 = Utf8 StackMapTable

#67 = Class #64 // "[Ljava/lang/String;"

#68 = Utf8 i

#69 = Utf8 I

#70 = Utf8 j

#71 = Utf8 SourceFile

#72 = Utf8 TestStackFrame.java

{

public TestStackFrame();

descriptor: ()V

flags: (0x0001) ACC_PUBLIC

Code:

stack=1, locals=1, args_size=1

0: aload_0

1: invokespecial #1 // Method java/lang/Object."":()V

4: return

LineNumberTable:

line 9: 0

LocalVariableTable:

Start Length Slot Name Signature

0 5 0 this LTestStackFrame;

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

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

flags: (0x0009) ACC_PUBLIC, ACC_STATIC

Code:

stack=2, locals=3, args_size=1

0: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

3: ldc #13 // String 这是main即将执行

5: invokevirtual #15 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

8: new #21 // class TestStackFrame

11: dup

12: invokespecial #23 // Method "":()V

15: astore_1

16: aload_1

17: invokevirtual #24 // Method method1:()V

20: goto 28

23: astore_2

24: aload_2

25: invokevirtual #29 // Method java/lang/Exception.printStackTrace:()V

28: aload_1

29: invokevirtual #24 // Method method1:()V

32: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

35: invokevirtual #32 // Method java/io/PrintStream.println:()V

38: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

41: ldc #34 // String 这是main执行完毕

43: invokevirtual #15 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

46: return

Exception table:

from to target type

16 20 23 Class java/lang/Exception

LineNumberTable:

line 13: 0

line 14: 8

line 16: 16

line 19: 20

line 17: 23

line 18: 24

line 20: 28

line 21: 32

line 22: 38

line 23: 46

LocalVariableTable:

Start Length Slot Name Signature

24 4 2 e Ljava/lang/Exception;

0 47 0 args [Ljava/lang/String;

16 31 1 tt LTestStackFrame;

StackMapTable: number_of_entries = 2

frame_type = 255 /* full_frame */

offset_delta = 23

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

stack = [ class java/lang/Exception ]

frame_type = 4 /* same */

public void method1();

descriptor: ()V

flags: (0x0001) ACC_PUBLIC

Code:

stack=2, locals=3, args_size=1

0: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

3: ldc #36 // String 这是method1即将执行

5: invokevirtual #15 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

8: bipush 10

10: istore_1

11: bipush 11

13: istore_2

14: aload_0

15: invokevirtual #38 // Method method2:()V

18: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

21: ldc #41 // String 这是method1执行完毕

23: invokevirtual #15 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

26: return

LineNumberTable:

line 26: 0

line 27: 8

line 28: 11

line 29: 14

line 32: 18

line 33: 26

LocalVariableTable:

Start Length Slot Name Signature

0 27 0 this LTestStackFrame;

11 16 1 I I

14 13 2 j I

public void method2();

descriptor: ()V

flags: (0x0001) ACC_PUBLIC

Code:

stack=2, locals=3, args_size=1

0: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

3: ldc #43 // String 这是method2即将执行

5: invokevirtual #15 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

8: bipush 10

10: istore_1

11: bipush 11

13: istore_2

14: aload_0

15: invokevirtual #45 // Method method3:()V

18: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

21: ldc #48 // String 这是method2执行完毕

23: invokevirtual #15 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

26: return

LineNumberTable:

line 35: 0

line 36: 8

line 37: 11

line 38: 14

line 39: 18

line 40: 26

LocalVariableTable:

Start Length Slot Name Signature

0 27 0 this LTestStackFrame;

11 16 1 I I

14 13 2 j I

public void method3();

descriptor: ()V

flags: (0x0001) ACC_PUBLIC

Code:

stack=2, locals=3, args_size=1

0: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

3: ldc #50 // String 这是method3即将执行

5: invokevirtual #15 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

8: bipush 10

10: istore_1

11: bipush 11

13: istore_2

14: getstatic #7 // Field java/lang/System.out:Ljava/io/PrintStream;

17: ldc #52 // String 这是method3执行完毕

19: invokevirtual #15 // Method java/io/PrintStream.println:(Ljava/lang/String;)V

22: return

LineNumberTable:

line 42: 0

line 43: 8

line 44: 11

line 45: 14

line 46: 22

LocalVariableTable:

Start Length Slot Name Signature

0 23 0 this LTestStackFrame;

11 12 1 I I

14 9 2 j I

}

SourceFile: "TestStackFrame.java"

a1234@MacBook-Pro learnJVMdemo %

3、在IDEA中利用jclasslib插件解析.class文件

首先需要在IDEA中安装jclasslib插件。进入IDEA的设置

image.png

在marketpalce中搜索jclasslib然后进行安装

在marketpalce中搜索jclasslib然后进行安装

安装好之后jclasslib出现在installed界面

安装好之后jclasslib出现在installed界面

重启IDEA，然后打开一个项目代码，在view窗口有一个show bytecode with jclasslib

image.png

点击，出现下面的界面，就可以从中获取到class文件相关的信息了

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