Question

我有一个带有简单java类的jar，如下所示

package org.debraj.pkgcmp.dummy;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

import com.google.common.annotations.VisibleForTesting;

public class PackageAnnotation {
    @VisibleForTesting
    public void dummyMethod() {

    }
}

用javap反编译类后，注释信息没有显示出来。

dmanna-m01:dummy dmanna$ javap PackageAnnotation.class
Compiled from "PackageAnnotation.java"
public class org.debraj.pkgcmp.dummy.PackageAnnotation {
  public org.debraj.pkgcmp.dummy.PackageAnnotation();
  public void dummyMethod();
}

即使@VisibleForTesting是RetentionPolicy.CLASS类型的注释，有人可以告诉我为什么反编译类中缺少注释信息吗？

dmanna-m01:dummy dmanna$ java -version
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)

番石榴版-23.5-jre

我已经看过这个question但是接受的答案在这里似乎没有用。根据Java doc

RetentionPolicy.class - 将在类中记录注释文件由编译器生成，但在运行时不需要由VM保留。

因此，javap应该能够显示RetentionPolicy.CLASS的注释信息。

修改

dmanna-m01:dummy dmanna$ javap -c PackageAnnotation.class
Compiled from "PackageAnnotation.java"
public class org.debraj.pkgcmp.dummy.PackageAnnotation {
  public org.debraj.pkgcmp.dummy.PackageAnnotation();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public void dummyMethod();
    Code:
       0: return
}

javap -v

的输出

dmanna-m01:dummy dmanna$ javap -v PackageAnnotation.class
Classfile /Users/dmanna/workspaces/java/eclipse/pkgcmp/target/classes/org/debraj/pkgcmp/dummy/PackageAnnotation.class
  Last modified Feb 14, 2018; size 489 bytes
  MD5 checksum 06949d127e5f631f77060be1b1f09b60
  Compiled from "PackageAnnotation.java"
public class org.debraj.pkgcmp.dummy.PackageAnnotation
  minor version: 0
  major version: 49
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Class              #2             // org/debraj/pkgcmp/dummy/PackageAnnotation
   #2 = Utf8               org/debraj/pkgcmp/dummy/PackageAnnotation
   #3 = Class              #4             // java/lang/Object
   #4 = Utf8               java/lang/Object
   #5 = Utf8               <init>
   #6 = Utf8               ()V
   #7 = Utf8               Code
   #8 = Methodref          #3.#9          // java/lang/Object."<init>":()V
   #9 = NameAndType        #5:#6          // "<init>":()V
  #10 = Utf8               LineNumberTable
  #11 = Utf8               LocalVariableTable
  #12 = Utf8               this
  #13 = Utf8               Lorg/debraj/pkgcmp/dummy/PackageAnnotation;
  #14 = Utf8               dummyMethod
  #15 = Utf8               RuntimeInvisibleAnnotations
  #16 = Utf8               Lcom/google/common/annotations/VisibleForTesting;
  #17 = Utf8               SourceFile
  #18 = Utf8               PackageAnnotation.java
{
  public org.debraj.pkgcmp.dummy.PackageAnnotation();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #8                  // Method java/lang/Object."<init>":()V
         4: return
      LineNumberTable:
        line 5: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       5     0  this   Lorg/debraj/pkgcmp/dummy/PackageAnnotation;

  public void dummyMethod();
    descriptor: ()V
    flags: ACC_PUBLIC
    RuntimeInvisibleAnnotations:
      0: #16()
    Code:
      stack=0, locals=1, args_size=1
         0: return
      LineNumberTable:
        line 9: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       1     0  this   Lorg/debraj/pkgcmp/dummy/PackageAnnotation;
}
SourceFile: "PackageAnnotation.java"

编辑2

如果我使用某些RUNTIME保留政策，我仍然没有在javap中看到注释（例如 - Subscribe）

package org.debraj.pkgcmp.dummy;

import com.google.common.eventbus.Subscribe;

public class PackageAnnotation {
    @Subscribe
    public void dummyMethod() {

    }
}

javap

的输出

dmanna-m01:dummy dmanna$ javap PackageAnnotation.class
Compiled from "PackageAnnotation.java"
public class org.debraj.pkgcmp.dummy.PackageAnnotation {
  public org.debraj.pkgcmp.dummy.PackageAnnotation();
  public void dummyMethod();
}

javap -c

的输出

dmanna-m01:dummy dmanna$ javap -c PackageAnnotation.class
Compiled from "PackageAnnotation.java"
public class org.debraj.pkgcmp.dummy.PackageAnnotation {
  public org.debraj.pkgcmp.dummy.PackageAnnotation();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public void dummyMethod();
    Code:
       0: return
}

javap -v

的输出

dmanna-m01:dummy dmanna$ javap -v PackageAnnotation.class
Classfile /Users/dmanna/workspaces/java/eclipse/pkgcmp/target/classes/org/debraj/pkgcmp/dummy/PackageAnnotation.class
  Last modified Feb 14, 2018; size 476 bytes
  MD5 checksum fd8b8e678ed771fa19193b73feae1acb
  Compiled from "PackageAnnotation.java"
public class org.debraj.pkgcmp.dummy.PackageAnnotation
  minor version: 0
  major version: 49
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #3.#16         // java/lang/Object."<init>":()V
   #2 = Class              #17            // org/debraj/pkgcmp/dummy/PackageAnnotation
   #3 = Class              #18            // java/lang/Object
   #4 = Utf8               <init>
   #5 = Utf8               ()V
   #6 = Utf8               Code
   #7 = Utf8               LineNumberTable
   #8 = Utf8               LocalVariableTable
   #9 = Utf8               this
  #10 = Utf8               Lorg/debraj/pkgcmp/dummy/PackageAnnotation;
  #11 = Utf8               dummyMethod
  #12 = Utf8               RuntimeVisibleAnnotations
  #13 = Utf8               Lcom/google/common/eventbus/Subscribe;
  #14 = Utf8               SourceFile
  #15 = Utf8               PackageAnnotation.java
  #16 = NameAndType        #4:#5          // "<init>":()V
  #17 = Utf8               org/debraj/pkgcmp/dummy/PackageAnnotation
  #18 = Utf8               java/lang/Object
{
  public org.debraj.pkgcmp.dummy.PackageAnnotation();
    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 5: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       5     0  this   Lorg/debraj/pkgcmp/dummy/PackageAnnotation;

  public void dummyMethod();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=0, locals=1, args_size=1
         0: return
      LineNumberTable:
        line 9: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       1     0  this   Lorg/debraj/pkgcmp/dummy/PackageAnnotation;
    RuntimeVisibleAnnotations:
      0: #13()
}
SourceFile: "PackageAnnotation.java"

javap没有在反编译类中显示注释信息

0 个答案: