最近在研究RPC框架，避免不了的就是在RPC调用中使用最多的则是动态代理的机制了，基于此，我们先来研究一下JDK动态代理
我们先来尝试着编写一下JDK动态代理的代码
- 由于JDK动态代理是基于接口的，所以不免需要先编写一个接口，并声明一个getHello方法
package cn.lonecloud.study.service;
import cn.lonecloud.study.dto.HelloDto;
public interface HelloService {
HelloDto getHello(String name);
}
- 有了接口，肯定是需要实现类，并将getHello方法给予实现
package cn.lonecloud.study;
import cn.lonecloud.study.dto.HelloDto;
import cn.lonecloud.study.service.HelloService;
public class HelloImpl implements HelloService {
@Override
public HelloDto getHello(String name) {
return new HelloDto();
}
}
这两个硬性条件有了，则我们来编写动态代理类了
- 首先我们先来了解两个API:
1. public static Object newProxyInstance(ClassLoader loader,Class[] interfaces,InvocationHandler h):该类用于创建动态代理类的实例，
1. loader:类的类加载器：一般用户类为AppClassLoader,可通过类名.class.getClassLoader()获得
2. interfaces:接口数组，前面我们说过，jdk动态代理是基于接口来实现的，所以这个参数就是用来传递接口数组啦
3. h:用于具体实现Handler,也就是这里执行相关的主要业务逻辑的地方了
2. InvocationHandler：该接口用于实现动态代理类的相关业务逻辑
1. 通常需要使用动态代理的话必须实现该接口，并重写其里面的invoke方法。
2. invoke(Object proxy, Method method, Object[] args)throws Throwable;
1. proxy:代理类对象
2. method:执行的方法
3. args:相关的参数
编写相关的代理类
package cn.lonecloud.study;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class ProxyDemo {
//定义实现类对象
Object target;
//构造函数
public ProxyDemo(Object target) {
this.target = target;
}
//获取实现类方法
@SuppressWarnings("unchecked")
public T getProxy(Class clazz){
//获取代理实例
return(T) Proxy.newProxyInstance(clazz.getClassLoader(),new Class[]{clazz}, (proxy, method, args) -> {
System.out.println(method.getName());
//执行代理对象
return method.invoke(target,args);
});
}
}
clazz.getClassLoader()获取的是类加载器，第二个参数创建了一个Class[]数组对象，由于传递过来的clazz为接口，所以可以这样写
执行：
HelloService proxy1 = new ProxyDemo(new HelloImpl()).getProxy(HelloService.class);
HelloDto demo = proxy1.getHello("demo");
我们来分析一下JDK生成动态的代理类究竟是个什么东西
- 将生成的代理类编程一个class文件，通过以下方法
public static void transClass() throws IOException {
URL resource = rpcMain.class.getClass().getResource("/");
byte[] bts = ProxyGenerator.generateProxyClass("$Proxy0", new Class[]{HelloService.class});
File file = new File(resource.getPath(),"$Proxy0.class");
if (!file.exists()){
file.createNewFile();
}
FileOutputStream fos = new FileOutputStream(file);
fos.write(bts);
fos.flush();
fos.close();
System.out.println(resource.getPath());
}
主要是通过ProxyGenerator.generateProxyClass获取代理类，该方法第一个为生成该类的名字，可以通过DEBUG的形式获取，第二个参数为该动态代理类所实现的接口，然后获取其字节码文件，将该字节码文件写入到文件中
- 通过JD-GUI反编译代码
import cn.lonecloud.study.dto.HelloDto;
import cn.lonecloud.study.service.HelloService;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
//该类集成了Proxy代理类，和实现了HelloService接口
public final class $Proxy0 extends Proxy implements HelloService {
//声明了一系列方法，为啥要声明这个呢？请看最后面的实现类
private static Method m1;
private static Method m3;
private static Method m2;
private static Method m0;
public $Proxy0(InvocationHandler var1) throws {
super(var1);
}
//重写Object类中equals方法
public final boolean equals(Object var1) throws {
try {
//都通过代理形式调用
return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
//实现getHello方法，通过代理形式
public final HelloDto getHello(String var1) throws {
try {
return (HelloDto)super.h.invoke(this, m3, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
//重写toString方法
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
//重写hashCode方法
public final int hashCode() throws {
try {
return (Integer)super.h.invoke(this, m0, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
//类初始化
static {
try {
//加载Object类，并获取其equals方法
m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
//加载HelloService接口，并获取其getHello方法
m3 = Class.forName("cn.lonecloud.study.service.HelloService").getMethod("getHello", Class.forName("java.lang.String"));
//加载Object类，并获取其toString方法
m2 = Class.forName("java.lang.Object").getMethod("toString");
//加载Object类，并获取其hashCode方法
m0 = Class.forName("java.lang.Object").getMethod("hashCode");
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}
- 将字节码通过 javap -verbose $Proxy0来获取字节码
Classfile /Users/lonecloud/Documents/ideaCode/target/classes/$Proxy0.class
Last modified 2018-6-9; size 2076 bytes
MD5 checksum a9c607b2d44135c7672b37458cc16c23
public final class $Proxy0 extends java.lang.reflect.Proxy implements cn.lonecloud.study.service.HelloService
minor version: 0
major version: 49
flags: ACC_PUBLIC, ACC_FINAL, ACC_SUPER
Constant pool:
#1 = Utf8
#2 = Utf8 (Ljava/lang/reflect/InvocationHandler;)V
#3 = Utf8 Code
#4 = Utf8 Exceptions
#5 = Utf8 java/lang/reflect/Proxy
#6 = Class #5 // java/lang/reflect/Proxy
#7 = NameAndType #1:#2 // "":(Ljava/lang/reflect/InvocationHandler;)V
#8 = Methodref #6.#7 // java/lang/reflect/Proxy."":(Ljava/lang/reflect/InvocationHandler;)V
#9 = Utf8 m1
#10 = Utf8 Ljava/lang/reflect/Method;
#11 = Utf8 equals
#12 = Utf8 (Ljava/lang/Object;)Z
#13 = Utf8 h
#14 = Utf8 Ljava/lang/reflect/InvocationHandler;
#15 = NameAndType #13:#14 // h:Ljava/lang/reflect/InvocationHandler;
#16 = Fieldref #6.#15 // java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
#17 = Utf8 $Proxy0
#18 = Class #17 // $Proxy0
#19 = NameAndType #9:#10 // m1:Ljava/lang/reflect/Method;
#20 = Fieldref #18.#19 // $Proxy0.m1:Ljava/lang/reflect/Method;
#21 = Utf8 java/lang/Object
#22 = Class #21 // java/lang/Object
#23 = Utf8 java/lang/reflect/InvocationHandler
#24 = Class #23 // java/lang/reflect/InvocationHandler
#25 = Utf8 invoke
#26 = Utf8 (Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;
#27 = NameAndType #25:#26 // invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;
#28 = InterfaceMethodref #24.#27 // java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;
#29 = Utf8 java/lang/Boolean
#30 = Class #29 // java/lang/Boolean
#31 = Utf8 booleanValue
#32 = Utf8 ()Z
#33 = NameAndType #31:#32 // booleanValue:()Z
#34 = Methodref #30.#33 // java/lang/Boolean.booleanValue:()Z
#35 = Utf8 java/lang/Error
#36 = Class #35 // java/lang/Error
#37 = Utf8 java/lang/RuntimeException
#38 = Class #37 // java/lang/RuntimeException
#39 = Utf8 java/lang/Throwable
#40 = Class #39 // java/lang/Throwable
#41 = Utf8 java/lang/reflect/UndeclaredThrowableException
#42 = Class #41 // java/lang/reflect/UndeclaredThrowableException
#43 = Utf8 (Ljava/lang/Throwable;)V
#44 = NameAndType #1:#43 // "":(Ljava/lang/Throwable;)V
#45 = Methodref #42.#44 // java/lang/reflect/UndeclaredThrowableException."":(Ljava/lang/Throwable;)V
#46 = Utf8 m3
#47 = Utf8 getHello
#48 = Utf8 (Ljava/lang/String;)Lcn/lonecloud/study/dto/HelloDto;
#49 = NameAndType #46:#10 // m3:Ljava/lang/reflect/Method;
#50 = Fieldref #18.#49 // $Proxy0.m3:Ljava/lang/reflect/Method;
#51 = Utf8 cn/lonecloud/study/dto/HelloDto
#52 = Class #51 // cn/lonecloud/study/dto/HelloDto
#53 = Utf8 m2
#54 = Utf8 toString
#55 = Utf8 ()Ljava/lang/String;
#56 = NameAndType #53:#10 // m2:Ljava/lang/reflect/Method;
#57 = Fieldref #18.#56 // $Proxy0.m2:Ljava/lang/reflect/Method;
#58 = Utf8 java/lang/String
#59 = Class #58 // java/lang/String
#60 = Utf8 m0
#61 = Utf8 hashCode
#62 = Utf8 ()I
#63 = NameAndType #60:#10 // m0:Ljava/lang/reflect/Method;
#64 = Fieldref #18.#63 // $Proxy0.m0:Ljava/lang/reflect/Method;
#65 = Utf8 java/lang/Integer
#66 = Class #65 // java/lang/Integer
#67 = Utf8 intValue
#68 = NameAndType #67:#62 // intValue:()I
#69 = Methodref #66.#68 // java/lang/Integer.intValue:()I
#70 = Utf8
#71 = Utf8 ()V
#72 = Utf8 java.lang.Object
#73 = String #72 // java.lang.Object
#74 = Utf8 java/lang/Class
#75 = Class #74 // java/lang/Class
#76 = Utf8 forName
#77 = Utf8 (Ljava/lang/String;)Ljava/lang/Class;
#78 = NameAndType #76:#77 // forName:(Ljava/lang/String;)Ljava/lang/Class;
#79 = Methodref #75.#78 // java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
#80 = String #11 // equals
#81 = Utf8 getMethod
#82 = Utf8 (Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
#83 = NameAndType #81:#82 // getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
#84 = Methodref #75.#83 // java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
#85 = Utf8 cn.lonecloud.study.service.HelloService
#86 = String #85 // cn.lonecloud.study.service.HelloService
#87 = String #47 // getHello
#88 = Utf8 java.lang.String
#89 = String #88 // java.lang.String
#90 = String #54 // toString
#91 = String #61 // hashCode
#92 = Utf8 java/lang/NoSuchMethodException
#93 = Class #92 // java/lang/NoSuchMethodException
#94 = Utf8 java/lang/NoSuchMethodError
#95 = Class #94 // java/lang/NoSuchMethodError
#96 = Utf8 getMessage
#97 = NameAndType #96:#55 // getMessage:()Ljava/lang/String;
#98 = Methodref #40.#97 // java/lang/Throwable.getMessage:()Ljava/lang/String;
#99 = Utf8 (Ljava/lang/String;)V
#100 = NameAndType #1:#99 // "":(Ljava/lang/String;)V
#101 = Methodref #95.#100 // java/lang/NoSuchMethodError."":(Ljava/lang/String;)V
#102 = Utf8 java/lang/ClassNotFoundException
#103 = Class #102 // java/lang/ClassNotFoundException
#104 = Utf8 java/lang/NoClassDefFoundError
#105 = Class #104 // java/lang/NoClassDefFoundError
#106 = Methodref #105.#100 // java/lang/NoClassDefFoundError."":(Ljava/lang/String;)V
#107 = Utf8 cn/lonecloud/study/service/HelloService
#108 = Class #107 // cn/lonecloud/study/service/HelloService
{
public $Proxy0(java.lang.reflect.InvocationHandler) throws ;
descriptor: (Ljava/lang/reflect/InvocationHandler;)V
flags: ACC_PUBLIC
Code:
stack=10, locals=2, args_size=2
0: aload_0
1: aload_1
2: invokespecial #8 // Method java/lang/reflect/Proxy."":(Ljava/lang/reflect/InvocationHandler;)V
5: return
Exceptions:
throws
public final boolean equals(java.lang.Object) throws ;
descriptor: (Ljava/lang/Object;)Z
flags: ACC_PUBLIC, ACC_FINAL
Code:
stack=10, locals=3, args_size=2
0: aload_0
1: getfield #16 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
4: aload_0
5: getstatic #20 // Field m1:Ljava/lang/reflect/Method;
8: iconst_1
9: anewarray #22 // class java/lang/Object
12: dup
13: iconst_0
14: aload_1
15: aastore
16: invokeinterface #28, 4 // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;
21: checkcast #30 // class java/lang/Boolean
24: invokevirtual #34 // Method java/lang/Boolean.booleanValue:()Z
27: ireturn
28: athrow
29: astore_2
30: new #42 // class java/lang/reflect/UndeclaredThrowableException
33: dup
34: aload_2
35: invokespecial #45 // Method java/lang/reflect/UndeclaredThrowableException."":(Ljava/lang/Throwable;)V
38: athrow
Exception table:
from to target type
0 28 28 Class java/lang/Error
0 28 28 Class java/lang/RuntimeException
0 28 29 Class java/lang/Throwable
Exceptions:
throws
public final cn.lonecloud.study.dto.HelloDto getHello(java.lang.String) throws ;
descriptor: (Ljava/lang/String;)Lcn/lonecloud/study/dto/HelloDto;
flags: ACC_PUBLIC, ACC_FINAL
Code:
stack=10, locals=3, args_size=2
0: aload_0
1: getfield #16 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
4: aload_0
5: getstatic #50 // Field m3:Ljava/lang/reflect/Method;
8: iconst_1
9: anewarray #22 // class java/lang/Object
12: dup
13: iconst_0
14: aload_1
15: aastore
16: invokeinterface #28, 4 // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;
21: checkcast #52 // class cn/lonecloud/study/dto/HelloDto
24: areturn
25: athrow
26: astore_2
27: new #42 // class java/lang/reflect/UndeclaredThrowableException
30: dup
31: aload_2
32: invokespecial #45 // Method java/lang/reflect/UndeclaredThrowableException."":(Ljava/lang/Throwable;)V
35: athrow
Exception table:
from to target type
0 25 25 Class java/lang/Error
0 25 25 Class java/lang/RuntimeException
0 25 26 Class java/lang/Throwable
Exceptions:
throws
public final java.lang.String toString() throws ;
descriptor: ()Ljava/lang/String;
flags: ACC_PUBLIC, ACC_FINAL
Code:
stack=10, locals=2, args_size=1
0: aload_0
1: getfield #16 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
4: aload_0
5: getstatic #57 // Field m2:Ljava/lang/reflect/Method;
8: aconst_null
9: invokeinterface #28, 4 // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;
14: checkcast #59 // class java/lang/String
17: areturn
18: athrow
19: astore_1
20: new #42 // class java/lang/reflect/UndeclaredThrowableException
23: dup
24: aload_1
25: invokespecial #45 // Method java/lang/reflect/UndeclaredThrowableException."":(Ljava/lang/Throwable;)V
28: athrow
Exception table:
from to target type
0 18 18 Class java/lang/Error
0 18 18 Class java/lang/RuntimeException
0 18 19 Class java/lang/Throwable
Exceptions:
throws
public final int hashCode() throws ;
descriptor: ()I
flags: ACC_PUBLIC, ACC_FINAL
Code:
stack=10, locals=2, args_size=1
0: aload_0
1: getfield #16 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
4: aload_0
5: getstatic #64 // Field m0:Ljava/lang/reflect/Method;
8: aconst_null
9: invokeinterface #28, 4 // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;
14: checkcast #66 // class java/lang/Integer
17: invokevirtual #69 // Method java/lang/Integer.intValue:()I
20: ireturn
21: athrow
22: astore_1
23: new #42 // class java/lang/reflect/UndeclaredThrowableException
26: dup
27: aload_1
28: invokespecial #45 // Method java/lang/reflect/UndeclaredThrowableException."":(Ljava/lang/Throwable;)V
31: athrow
Exception table:
from to target type
0 21 21 Class java/lang/Error
0 21 21 Class java/lang/RuntimeException
0 21 22 Class java/lang/Throwable
Exceptions:
throws
static {} throws ;
descriptor: ()V
flags: ACC_STATIC
Code:
stack=10, locals=2, args_size=0
0: ldc #73 // String java.lang.Object
2: invokestatic #79 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
5: ldc #80 // String equals
7: iconst_1
8: anewarray #75 // class java/lang/Class
11: dup
12: iconst_0
13: ldc #73 // String java.lang.Object
15: invokestatic #79 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
18: aastore
19: invokevirtual #84 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
22: putstatic #20 // Field m1:Ljava/lang/reflect/Method;
25: ldc #86 // String cn.lonecloud.study.service.HelloService
27: invokestatic #79 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
30: ldc #87 // String getHello
32: iconst_1
33: anewarray #75 // class java/lang/Class
36: dup
37: iconst_0
38: ldc #89 // String java.lang.String
40: invokestatic #79 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
43: aastore
44: invokevirtual #84 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
47: putstatic #50 // Field m3:Ljava/lang/reflect/Method;
50: ldc #73 // String java.lang.Object
52: invokestatic #79 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
55: ldc #90 // String toString
57: iconst_0
58: anewarray #75 // class java/lang/Class
61: invokevirtual #84 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
64: putstatic #57 // Field m2:Ljava/lang/reflect/Method;
67: ldc #73 // String java.lang.Object
69: invokestatic #79 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
72: ldc #91 // String hashCode
74: iconst_0
75: anewarray #75 // class java/lang/Class
78: invokevirtual #84 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
81: putstatic #64 // Field m0:Ljava/lang/reflect/Method;
84: return
85: astore_1
86: new #95 // class java/lang/NoSuchMethodError
89: dup
90: aload_1
91: invokevirtual #98 // Method java/lang/Throwable.getMessage:()Ljava/lang/String;
94: invokespecial #101 // Method java/lang/NoSuchMethodError."":(Ljava/lang/String;)V
97: athrow
98: astore_1
99: new #105 // class java/lang/NoClassDefFoundError
102: dup
103: aload_1
104: invokevirtual #98 // Method java/lang/Throwable.getMessage:()Ljava/lang/String;
107: invokespecial #106 // Method java/lang/NoClassDefFoundError."":(Ljava/lang/String;)V
110: athrow
Exception table:
from to target type
0 85 85 Class java/lang/NoSuchMethodException
0 85 98 Class java/lang/ClassNotFoundException
Exceptions:
throws
总结: 代理对象生成类：
该代理对象会将该接口的的方法进行一次封装通过调用super.h.invoke(this, m0, (Object[])null);将执行之前定义的InvolicationHandler类中的invoke方法然后再调用我们之前编写的类方法。
会将Object类中的toString,equals,hashCode这些方法进行代理
将InvocationHandler通过成员变量的形式传递到类中