Github源碼下載地址:https://github.com/chenxingxing6/sourcecode/tree/master/code-proxy
一、前言
我們知道常見的動態代理有兩種實現方式,基於jdk實現動態代理,基於cglib實現動態代理。本篇博客將自已模仿jdk實現接口動態代理,自己手寫源碼,實現一個接口的動態代理。
二、實現接口動態代理
如果不瞭解jdk動態代理的,先去了解一下,在來看此文章…
2.1動態代理原理圖
Proxy通過(interfaces/invocationHandler)生成代理類 $Proxy0;
Proxy通過ClassLoader來加載生成的代理類$Proxy0的字節碼文件;
2.2自己實現
2.2.1 目錄結構
2.2.2 實現原理圖
2.2.3 自定義InvocationHandler
package com.my;
import java.lang.reflect.Method;
/**
* @Author: cxx
* @Date: 2019/10/2 11:11
*/
public interface MyInvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable;
}
2.2.4 自定義MyClassLoader
package com.my;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
/**
* @Author: cxx
* @Date: 2019/10/2 14:24
*/
public class MyClassLoader extends ClassLoader{
private String baseDir;
public MyClassLoader() {
this.baseDir = this.getClass().getResource("").getFile();
}
@Override
protected Class<?> findClass(String name) throws ClassNotFoundException {
String className = this.getClass().getPackage().getName() + "." + name;
if (baseDir != null && baseDir != ""){
File f = new File(baseDir + "/" + name +".class");
ByteArrayOutputStream out = null;
FileInputStream fis = null;
if (f.exists()){
try {
fis = new FileInputStream(f);
out = new ByteArrayOutputStream();
byte[] b = new byte[1024];
int len;
while ((len = fis.read(b)) != -1){
out.write(b, 0, len);
}
return defineClass(className, out.toByteArray(), 0, out.size());
}catch (Exception e){
e.printStackTrace();
}finally {
if (fis != null){
try {
fis.close();
}catch (Exception e){
e.printStackTrace();
}
}
if (out != null){
try {
out.close();
}catch (Exception e){
e.printStackTrace();
}
}
// 查看.class文件
f.delete();
}
}
}
return null;
}
}
爲什麼要定義一個自定義的類加載器呢?它的作用是什麼呢?
想手寫JDK動態代理,那麼我們將自己在內存中生成動態代理類加載到jvm,重寫了findClass方法,就是爲了在指定路徑下加載指定的字節碼文件。
2.2.5 自定義MyProxy
自己實現代理類MyProxy,步驟分爲以下5步
1.生成java源碼
2.將源碼輸出到java文件中
3.將java文件編譯成class文件
4.將class加載進jvm
5.返回代理類對象
package com.my;
import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.io.Serializable;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
/**
* @Author: cxx
* @Date: 2019/10/2 11:14
*/
public class MyProxy implements Serializable {
private static final String ln = "\r\n";
public static Object newProxyInstance(MyClassLoader classLoader, Class<?>[] interfaces, MyInvocationHandler myInvocationHandler){
File file = null;
try {
// 1.獲取java源碼,並輸出到文件
String source = generateSrc(interfaces);
String filePath = MyProxy.class.getResource("").getPath();
file = new File(filePath + "$Proxy0.java");
FileWriter fw = new FileWriter(file);
fw.write(source);
fw.flush();
fw.close();
// 2.對源碼進行編譯
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);
Iterable iterable = fileManager.getJavaFileObjects(file);
JavaCompiler.CompilationTask task = compiler.getTask(null, fileManager, null, null, null, iterable);
task.call();
fileManager.close();
// 3.加載class文件到jvm
Class proxyClass = classLoader.findClass("$Proxy0");
// 4.返回代理對象
Constructor c = proxyClass.getConstructor(MyInvocationHandler.class);
return c.newInstance(myInvocationHandler);
}catch (Exception e){
e.printStackTrace();
}finally {
file.delete();
}
return null;
}
/**
* 獲取源碼,動態生成java類,看$ProxyMy
* @param interfaces
* @return
*/
private static String generateSrc(Class<?>[] interfaces) {
StringBuffer sb = new StringBuffer();
sb.append("package com.my;" + ln);
sb.append("import java.lang.reflect.Method;" + ln);
sb.append("public class $Proxy0 implements " + interfaces[0].getName() + "{" + ln);
sb.append("private MyInvocationHandler h;"+ln);
sb.append("public $Proxy0(MyInvocationHandler h) { " + ln);
sb.append("this.h = h;"+ln);
sb.append("}" + ln);
for (Method m : interfaces[0].getMethods()) {
sb.append("public " + m.getReturnType().getName() + " "
+ m.getName() + "(String id) {" + ln);
sb.append("try{" + ln);
sb.append("Method m = " + interfaces[0].getName()
+ ".class.getMethod(\"" + m.getName()
+ "\",String.class);" + ln);
sb.append("this.h.invoke(this,m,new Object[]{id});" + ln);
sb.append("}catch(Throwable e){" + ln);
sb.append("e.printStackTrace();" + ln);
sb.append("}"+ln);
sb.append("}"+ln);
}
sb.append("}" + ln);
return sb.toString();
}
}
2.2.6 最終生成$MyProxy.java
生成代理類
package com.my;
import com.IUserService;
import java.lang.reflect.Method;
/**
* @Author: cxx
* @Date: 2019/10/2 11:29
* 動態生成代理類:如下
*/
public class $ProxyMy implements IUserService {
private MyInvocationHandler invocationHandler;
public $ProxyMy(MyInvocationHandler invocationHandler) {
this.invocationHandler = invocationHandler;
}
public void delete(String id) {
try {
Method m = IUserService.class.getMethod("delete", String.class);
invocationHandler.invoke(this, m, new Object[]{id});
} catch (Throwable throwable) {
throwable.printStackTrace();
}
}
}
2.2.7 測試
package com.my;
import com.IUserService;
import com.UserService;
import java.lang.reflect.Method;
/**
* @Author: cxx
* @Date: 2019/10/2 11:13
*/
public class MyTest {
public static void main(String[] args) {
IUserService userServiceProxy = (IUserService) MyProxy.newProxyInstance(
new MyClassLoader(),
UserService.class.getInterfaces(),
new MyInvocationHandler() {
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("before");
method.invoke(new UserService(), args);
System.out.println("after");
return null;
}
}
);
userServiceProxy.delete("100");
}
}
結果
Connected to the target VM, address: ‘127.0.0.1:49209’, transport: ‘socket’
Disconnected from the target VM, address: ‘127.0.0.1:49209’, transport: ‘socket’
before
刪除用戶 id:100
after