java注解是怎么实现的

$ java -version java version "1.8.0_20" Java(TM) SE Runtime Environment (build 1.8.0_20-b26) Java HotSpot(TM) 64-Bit Server VM (build 25.20-b23, mixed mode) 

/**  * The common interface extended by all annotation types.  Note that an  * interface that manually extends this one does <i>not</i> define  * an annotation type.  Also note that this interface does not itself  * define an annotation type.  *  * More information about annotation types can be found in section 9.6 of  * <cite>The Java&trade; Language Specification</cite>.  *  * The {@link java.lang.reflect.AnnotatedElement} interface discusses  * compatibility concerns when evolving an annotation type from being  * non-repeatable to being repeatable.  *  * @author  Josh Bloch  * @since   1.5  */ public interface Annotation {     ... } 

import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target;  /**  * Created by Administrator on 2015/1/18.  */ @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) public @interface TestAnnotation {      int count() default 1;  } 

Classfile /e:/workspace/intellij/SpringTest/target/classes/TestAnnotation.class   Last modified 2015-1-18; size 379 bytes   MD5 checksum 200dc3a75216b7a88ae17873d5dffd4f   Compiled from "TestAnnotation.java" public interface TestAnnotation extends java.lang.annotation.Annotation   minor version: 0   major version: 52   flags: ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT, ACC_ANNOTATION Constant pool:    #1 = Class              #14            // TestAnnotation    #2 = Class              #15            // java/lang/Object    #3 = Class              #16            // java/lang/annotation/Annotation    #4 = Utf8               SourceFile    #5 = Utf8               TestAnnotation.java    #6 = Utf8               RuntimeVisibleAnnotations    #7 = Utf8               Ljava/lang/annotation/Target;    #8 = Utf8               value    #9 = Utf8               Ljava/lang/annotation/ElementType;   #10 = Utf8               TYPE   #11 = Utf8               Ljava/lang/annotation/Retention;   #12 = Utf8               Ljava/lang/annotation/RetentionPolicy;   #13 = Utf8               RUNTIME   #14 = Utf8               TestAnnotation   #15 = Utf8               java/lang/Object   #16 = Utf8               java/lang/annotation/Annotation { } SourceFile: "TestAnnotation.java" RuntimeVisibleAnnotations:   0: #7(#8=[e#9.#10])   1: #11(#8=e#12.#13) 

import java.io.IOException;  /**  * Created by Administrator on 2015/1/18.  */ @TestAnnotation(count = 0x7fffffff) public class TestMain {      public static void main(String[] args) throws InterruptedException, NoSuchFieldException, IllegalAccessException, IOException {         TestAnnotation annotation = TestMain.class.getAnnotation(TestAnnotation.class);         System.out.println(annotation.count());         System.in.read();     }  } 

Classfile /e:/workspace/intellij/SpringTest/target/classes/TestMain.class   Last modified 2015-1-20; size 1006 bytes   MD5 checksum a2d5367ea568240f078d5fb1de917550   Compiled from "TestMain.java" public class TestMain   minor version: 0   major version: 52   flags: ACC_PUBLIC, ACC_SUPER Constant pool:    #1 = Methodref          #10.#34        // java/lang/Object."<init>":()V    #2 = Class              #35            // TestMain    #3 = Class              #36            // TestAnnotation    #4 = Methodref          #37.#38        // java/lang/Class.getAnnotation:(Ljava/lang/Class;)Ljava/lang/annotation/Annotation;    #5 = Fieldref           #39.#40        // java/lang/System.out:Ljava/io/PrintStream;    #6 = InterfaceMethodref #3.#41         // TestAnnotation.count:()I    #7 = Methodref          #42.#43        // java/io/PrintStream.println:(I)V    #8 = Fieldref           #39.#44        // java/lang/System.in:Ljava/io/InputStream;    #9 = Methodref          #45.#46        // java/io/InputStream.read:()I   #10 = Class              #47            // java/lang/Object   #11 = Utf8               <init>   #12 = Utf8               ()V   #13 = Utf8               Code   #14 = Utf8               LineNumberTable   #15 = Utf8               LocalVariableTable   #16 = Utf8               this   #17 = Utf8               LTestMain;   #18 = Utf8               main   #19 = Utf8               ([Ljava/lang/String;)V   #20 = Utf8               args   #21 = Utf8               [Ljava/lang/String;   #22 = Utf8               annotation   #23 = Utf8               LTestAnnotation;   #24 = Utf8               Exceptions   #25 = Class              #48            // java/lang/InterruptedException   #26 = Class              #49            // java/lang/NoSuchFieldException   #27 = Class              #50            // java/lang/IllegalAccessException   #28 = Class              #51            // java/io/IOException   #29 = Utf8               SourceFile   #30 = Utf8               TestMain.java   #31 = Utf8               RuntimeVisibleAnnotations   #32 = Utf8               count   #33 = Integer            2147483647   #34 = NameAndType        #11:#12        // "<init>":()V   #35 = Utf8               TestMain   #36 = Utf8               TestAnnotation   #37 = Class              #52            // java/lang/Class   #38 = NameAndType        #53:#54        // getAnnotation:(Ljava/lang/Class;)Ljava/lang/annotation/Annotation;   #39 = Class              #55            // java/lang/System   #40 = NameAndType        #56:#57        // out:Ljava/io/PrintStream;   #41 = NameAndType        #32:#58        // count:()I   #42 = Class              #59            // java/io/PrintStream   #43 = NameAndType        #60:#61        // println:(I)V   #44 = NameAndType        #62:#63        // in:Ljava/io/InputStream;   #45 = Class              #64            // java/io/InputStream   #46 = NameAndType        #65:#58        // read:()I   #47 = Utf8               java/lang/Object   #48 = Utf8               java/lang/InterruptedException   #49 = Utf8               java/lang/NoSuchFieldException   #50 = Utf8               java/lang/IllegalAccessException   #51 = Utf8               java/io/IOException   #52 = Utf8               java/lang/Class   #53 = Utf8               getAnnotation   #54 = Utf8               (Ljava/lang/Class;)Ljava/lang/annotation/Annotation;   #55 = Utf8               java/lang/System   #56 = Utf8               out   #57 = Utf8               Ljava/io/PrintStream;   #58 = Utf8               ()I   #59 = Utf8               java/io/PrintStream   #60 = Utf8               println   #61 = Utf8               (I)V   #62 = Utf8               in   #63 = Utf8               Ljava/io/InputStream;   #64 = Utf8               java/io/InputStream   #65 = Utf8               read {   public TestMain();     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 7: 0       LocalVariableTable:         Start  Length  Slot  Name   Signature             0       5     0  this   LTestMain;    public static void main(java.lang.String[]) throws java.lang.InterruptedException, java.lang.NoSuchFieldException, java.lang.IllegalAccessException, java.io.IOException;     descriptor: ([Ljava/lang/String;)V     flags: ACC_PUBLIC, ACC_STATIC     Code:       stack=2, locals=2, args_size=1          0: ldc           #2                  // class TestMain          2: ldc           #3                  // class TestAnnotation          4: invokevirtual #4                  // Method java/lang/Class.getAnnotation:(Ljava/lang/Class;)Ljava/lang/annotation/Annotation;          7: checkcast     #3                  // class TestAnnotation         10: astore_1         11: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;         14: aload_1         15: invokeinterface #6,  1            // InterfaceMethod TestAnnotation.count:()I         20: invokevirtual #7                  // Method java/io/PrintStream.println:(I)V         23: getstatic     #8                  // Field java/lang/System.in:Ljava/io/InputStream;         26: invokevirtual #9                  // Method java/io/InputStream.read:()I         29: pop         30: return       LineNumberTable:         line 10: 0         line 11: 11         line 12: 23         line 13: 30       LocalVariableTable:         Start  Length  Slot  Name   Signature             0      31     0  args   [Ljava/lang/String;            11      20     1 annotation   LTestAnnotation;     Exceptions:       throws java.lang.InterruptedException, java.lang.NoSuchFieldException, java.lang.IllegalAccessException, java.io.IOException } SourceFile: "TestMain.java" RuntimeVisibleAnnotations:   0: #23(#32=I#33) 

hsdb> scanoops 0x00000000e1b80000 0x00000000e3300000 TestAnnotation 0x00000000e1d6c360 com/sun/proxy/$Proxy1 

Classfile /e:/workspace/intellij/SpringTest/target/classes/com/sun/proxy/$Proxy1.class   Last modified 2015-1-19; size 2062 bytes   MD5 checksum 7321e44402258ba9e061275e313c5c9f public final class com.sun.proxy.$Proxy1 extends java.lang.reflect.Proxy implements TestAnnotation   minor version: 0   major version: 49   flags: ACC_PUBLIC, ACC_FINAL ... 

hsdb> inspect 0x00000000e1d6c360 instance of Oop for com/sun/proxy/$Proxy1 @ 0x00000000e1d6c360 @ 0x00000000e1d6c360 (size = 16) _mark: 1 _metadata._compressed_klass: InstanceKlass for com/sun/proxy/$Proxy1 h: Oop for sun/reflect/annotation/AnnotationInvocationHandler @ 0x00000000e1ce7670 Oop for sun/reflect/annotation/Annota tionInvocationHandler @ 0x00000000e1ce7670 

hsdb> inspect 0x00000000e1ce7670 instance of Oop for sun/reflect/annotation/AnnotationInvocationHandler @ 0x00000000e1ce7670 @ 0x00000000e1ce7670 (size =  24) _mark: 1 _metadata._compressed_klass: InstanceKlass for sun/reflect/annotation/AnnotationInvocationHandler type: Oop for java/lang/Class @ 0x00000000e1ccc5f8 Oop for java/lang/Class @ 0x00000000e1ccc5f8 memberValues: Oop for java/util/LinkedHashMap @ 0x00000000e1ce7548 Oop for java/util/LinkedHashMap @ 0x00000000e1ce7548 memberMethods: null null hsdb> inspect 0x00000000e1ce7548 instance of Oop for java/util/LinkedHashMap @ 0x00000000e1ce7548 @ 0x00000000e1ce7548 (size = 56) _mark: 1 _metadata._compressed_klass: InstanceKlass for java/util/LinkedHashMap keySet: null null values: null null table: ObjArray @ 0x00000000e1ce75b8 Oop for [Ljava/util/HashMap$Node; @ 0x00000000e1ce75b8 entrySet: null null size: 1 modCount: 1 threshold: 1 loadFactor: 0.75 head: Oop for java/util/LinkedHashMap$Entry @ 0x00000000e1ce75d0 Oop for java/util/LinkedHashMap$Entry @ 0x00000000e1ce7 5d0 tail: Oop for java/util/LinkedHashMap$Entry @ 0x00000000e1ce75d0 Oop for java/util/LinkedHashMap$Entry @ 0x00000000e1ce75d0 accessOrder: false hsdb> inspect 0x00000000e1ce75d0 instance of Oop for java/util/LinkedHashMap$Entry @ 0x00000000e1ce75d0 @ 0x00000000e1ce75d0 (size = 40) _mark: 1 _metadata._compressed_klass: InstanceKlass for java/util/LinkedHashMap$Entry hash: 94852264 key: "count" @ 0x00000000e1bd7c90 Oop for java/lang/String @ 0x00000000e1bd7c90 value: Oop for java/lang/Integer @ 0x00000000e1ce7630 Oop for java/lang/Integer @ 0x00000000e1ce7630 next: null null before: null null after: null null hsdb> inspect 0x00000000e1ce7630 instance of Oop for java/lang/Integer @ 0x00000000e1ce7630 @ 0x00000000e1ce7630 (size = 16) _mark: 1 _metadata._compressed_klass: InstanceKlass for java/lang/Integer value: 2147483647