字节码增强技术探索

发表于 2019-09-08 更新于 2022-05-28 分类于 java 阅读次数： Waline：本文字数： 4k 阅读时长 ≈ 4 分钟

[wkq@VM_77_25_centos java_test]$  vi HelloWorld.java
[wkq@VM_77_25_centos java_test]$
[wkq@VM_77_25_centos java_test]$ javac HelloWorld.java
[wkq@VM_77_25_centos java_test]$
[wkq@VM_77_25_centos java_test]$ java HelloWorld
Hello, World!
[wkq@VM_77_25_centos java_test]$ javap -v HelloWorld.class

public class HelloWorld{
	public static void main(String[] args){
		System.out.println("Hello, World!");
	}
}

反编译后的内容如下:

Classfile /home/wkq/workspaces/java_test/HelloWorld.class
  Last modified Jun 21, 2020; size 427 bytes
  MD5 checksum 15d19d1074b862ce9cca6a8a7f6ee8fe
  Compiled from "HelloWorld.java"
public class HelloWorld
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #6.#15         // java/lang/Object."<init>":()V
   #2 = Fieldref           #16.#17        // java/lang/System.out:Ljava/io/PrintStream;
   #3 = String             #18            // Hello, World!
   #4 = Methodref          #19.#20        // java/io/PrintStream.println:(Ljava/lang/String;)V
   #5 = Class              #21            // HelloWorld
   #6 = Class              #22            // java/lang/Object
   #7 = Utf8               <init>
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               main
  #12 = Utf8               ([Ljava/lang/String;)V
  #13 = Utf8               SourceFile
  #14 = Utf8               HelloWorld.java
  #15 = NameAndType        #7:#8          // "<init>":()V
  #16 = Class              #23            // java/lang/System
  #17 = NameAndType        #24:#25        // out:Ljava/io/PrintStream;
  #18 = Utf8               Hello, World!
  #19 = Class              #26            // java/io/PrintStream
  #20 = NameAndType        #27:#28        // println:(Ljava/lang/String;)V
  #21 = Utf8               HelloWorld
  #22 = Utf8               java/lang/Object
  #23 = Utf8               java/lang/System
  #24 = Utf8               out
  #25 = Utf8               Ljava/io/PrintStream;
  #26 = Utf8               java/io/PrintStream
  #27 = Utf8               println
  #28 = Utf8               (Ljava/lang/String;)V
{
  public HelloWorld();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: return
      LineNumberTable:
        line 2: 0

  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=1, args_size=1
         0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #3                  // String Hello, World!
         5: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: return
      LineNumberTable:
        line 4: 0
        line 5: 8
}
SourceFile: "HelloWorld.java"

[wkq@VM_77_25_centos java_test]$  vi CountPlus.java
[wkq@VM_77_25_centos java_test]$
[wkq@VM_77_25_centos java_test]$ javac CountPlus.java
[wkq@VM_77_25_centos java_test]$ java CountPlus
2
[wkq@VM_77_25_centos java_test]$
[wkq@VM_77_25_centos java_test]$ javap -v CountPlus.class

public class CountPlus {
    public static void main(String[] args) {
        int x = 1;
        x++;
        System.out.println(x);
    }

}

Classfile /home/wkq/workspaces/java_test/CountPlus.class
  Last modified Jun 21, 2020; size 401 bytes
  MD5 checksum a5d707b751fcd06e1c14854e84aafe07
  Compiled from "CountPlus.java"
public class CountPlus
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #5.#14         // java/lang/Object."<init>":()V
   #2 = Fieldref           #15.#16        // java/lang/System.out:Ljava/io/PrintStream;
   #3 = Methodref          #17.#18        // java/io/PrintStream.println:(I)V
   #4 = Class              #19            // CountPlus
   #5 = Class              #20            // java/lang/Object
   #6 = Utf8               <init>
   #7 = Utf8               ()V
   #8 = Utf8               Code
   #9 = Utf8               LineNumberTable
  #10 = Utf8               main
  #11 = Utf8               ([Ljava/lang/String;)V
  #12 = Utf8               SourceFile
  #13 = Utf8               CountPlus.java
  #14 = NameAndType        #6:#7          // "<init>":()V
  #15 = Class              #21            // java/lang/System
  #16 = NameAndType        #22:#23        // out:Ljava/io/PrintStream;
  #17 = Class              #24            // java/io/PrintStream
  #18 = NameAndType        #25:#26        // println:(I)V
  #19 = Utf8               CountPlus
  #20 = Utf8               java/lang/Object
  #21 = Utf8               java/lang/System
  #22 = Utf8               out
  #23 = Utf8               Ljava/io/PrintStream;
  #24 = Utf8               java/io/PrintStream
  #25 = Utf8               println
  #26 = Utf8               (I)V
{
  public CountPlus();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: return
      LineNumberTable:
        line 1: 0

  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=2, args_size=1
         0: iconst_1
         1: istore_1
         2: iinc          1, 1
         5: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
         8: iload_1
         9: invokevirtual #3                  // Method java/io/PrintStream.println:(I)V
        12: return
      LineNumberTable:
        line 3: 0
        line 4: 2
        line 5: 5
        line 6: 12
}
SourceFile: "CountPlus.java"

References

[1] 字节码增强技术探索
 https://cyw3.github.io/YalesonChan/2016/Java-Byte-Code.html
https://juejin.im/post/5aca2c366fb9a028c97a5609