引言
項目結構如下圖所示，maven項目
1、JDK動態代理
先來一段jdk動態代理的demo，
首先創建一個接口，Person
package bean;
public interface Person {
public void eat();
}
然后寫一個實現類PersonImpl
package bean;
public class PersonImpl implements Person{
@Override
public void eat() {
// TODO Auto-generated method stub
System.out.println("time to eat ");
}
}
然后寫個使用類PersonInvocationHandler
package jdk;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
public class PersonInvocationHandler implements InvocationHandler {
private Object obj;
public PersonInvocationHandler(Object obj) {
this.obj = obj;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
// TODO Auto-generated method stub
System.out.println("before time to eat");
method.invoke(obj, args);
System.out.println("after time to eat");
return null;
}
}
最后 再寫個測試類
package jdk;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.lang.reflect.Proxy;
import sun.misc.ProxyGenerator;
import bean.Person;
import bean.PersonImpl;
public class jdkTest {
public static void main(String[] args) throws Exception {
PersonInvocationHandler personInvocationHandler = new PersonInvocationHandler(
new PersonImpl());
Person personProxy = (Person) Proxy.newProxyInstance(
PersonImpl.class.getClassLoader(),
PersonImpl.class.getInterfaces(), personInvocationHandler);
personProxy.eat();
}
}
輸出如下
before time to eat
time to eat
after time to eat
接下里我們不使用JDK的API，自己實現一套代理類
2、自定義動態代理
先上測試類的代碼，如下圖所示，共有(1)(2)(3)處不同
針對(1)，我們有如下代碼,先抄襲JDK的InvocationHandler，改個名字成為MyInvocationHandler
package custom;
import java.lang.reflect.Method;
public interface MyInvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable;
}
編寫一個JAVA類MyPersonInvocationHandler繼承MyInvocationHandler，這段代碼與PersonInvocationHandler的代碼無異，如下所示
package custom;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
public class MyPersonInvocationHandler implements MyInvocationHandler {
private Object obj;
public MyPersonInvocationHandler(Object obj) {
this.obj = obj;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
// TODO Auto-generated method stub
System.out.println("before time to eat");
method.invoke(obj, args);
System.out.println("after time to eat");
return null;
}
}
針對(2),我們實現一個自己的代理生成類MyProxy,其生成java代理類的步驟分為以下5步
- 生成java源碼
- 將源碼輸出到java文件中
- 將java文件編譯成class文件
- 將class加載進jvm
- 返回代理類對象
具體代碼如下
package custom;
import java.io.File;
import java.io.FileWriter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
public class MyProxy {
public static final String ln = "\r\n";
public static Object newProxyInstance(MyClassLoader myClassLoder,
Class<?>[] interfaces, MyInvocationHandler h) {
try{
// 1 java源碼
String src = generateSrc(interfaces);
// 2 將源碼輸出到java文件中
String filePath = MyProxy.class.getResource("").getPath();
System.out.println(filePath);
File f = new File(filePath + "$Proxy0.java");
FileWriter fw = new FileWriter(f);
fw.write(src);
fw.flush();
fw.close();
//3、將java文件編譯成class文件
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager manage = compiler.getStandardFileManager(null,null,null);
Iterable iterable = manage.getJavaFileObjects(f);
JavaCompiler.CompilationTask task = compiler.getTask(null,manage,null,null,null,iterable);
task.call();
manage.close();
//4、將class加載進jvm
Class proxyClass=myClassLoder.findClass("$Proxy0");
f.delete();
//5、返回代理類對象
Constructor constructor = proxyClass.getConstructor(MyInvocationHandler.class);
return constructor.newInstance(h);
}catch(Exception e){
e.printStackTrace();
}
return null;
}
private static String generateSrc(Class<?>[] interfaces) {
// TODO Auto-generated method stub
StringBuffer sb = new StringBuffer();
sb.append("package custom;" + 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() + "() {" + ln);
sb.append("try{" + ln);
sb.append("Method m = " + interfaces[0].getName()
+ ".class.getMethod(\"" + m.getName()
+ "\",new Class[]{});" + ln);
sb.append("this.h.invoke(this,m,null);" + ln);
sb.append("}catch(Throwable e){" + ln);
sb.append("e.printStackTrace();" + ln);
sb.append("}"+ln);
sb.append("}"+ln);
}
sb.append("}" + ln);
return sb.toString();
}
}
針對(3)，我們繼承ClassLoader,實現一套自己的類加載機制MyClassLoader，如下所示,
package custom;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
public class MyClassLoader extends ClassLoader {
private File classPathfile;
public MyClassLoader() {
String classpth = MyClassLoader.class.getResource("").getPath();
classPathfile = new File(classpth);
}
@Override
public Class<?> findClass(String name) throws ClassNotFoundException {
String className = MyClassLoader.class.getPackage().getName() + "." +name;
if (classPathfile != null) {
File file = new File(classPathfile, name + ".class");
FileInputStream fileInputStream = null;
ByteArrayOutputStream outputStream = null;
try{
fileInputStream = new FileInputStream(file);
outputStream = new ByteArrayOutputStream();
byte[] buff = new byte[1024];
int len;
while((len=fileInputStream.read(buff))!=-1){
outputStream.write(buff, 0, len);
}
return defineClass(className, outputStream.toByteArray(), 0, outputStream.size());
}catch(Exception e){
e.printStackTrace();
}finally{
if(null!=fileInputStream){
try {
fileInputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(null!=outputStream){
try {
outputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
return null;
}
}
最后測試類代碼如下所示
package custom;
import java.lang.reflect.Proxy;
import custom.MyPersonInvocationHandler;
import bean.Person;
import bean.PersonImpl;
public class CustomTest {
public static void main(String[] args) {
MyPersonInvocationHandler personInvocationHandler = new MyPersonInvocationHandler(
new PersonImpl());
Person personProxy = (Person) MyProxy.newProxyInstance(
new MyClassLoader(), PersonImpl.class.getInterfaces(),
personInvocationHandler);
personProxy.eat();
}
}
輸出如何所示
before time to eat
time to eat
after time to eat
至此，我們已完全實現了一套自定義的jdk動態代理類