前言
根据Java Porxy 实现原理实现我们手写的自定义代理类，实现简易的动态代理流程。
自定义InvocationHandler
package com.drj.bj.proxy.drjproxy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public interface DrjInvocationHandler {
public Object invoke(Object object, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException;
}
自定义类加载器
package com.drj.bj.proxy.drjproxy;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
public class DrjClassLoader extends ClassLoader {
private File classPathFile;
public DrjClassLoader() {
String classPath = DrjClassLoader.class.getResource("").getPath();
this.classPathFile = new File(classPath);
}
@Override
protected Class<?> findClass(String name) throws ClassNotFoundException {
String className = DrjClassLoader.class.getPackage().getName() + "." + name;
if (classPathFile != null) {
File classFile = new File(classPathFile, name.replaceAll("\\.", "/") + ".class");
if (classFile.exists()) {
FileInputStream in = null;
ByteArrayOutputStream out = null;
try {
in = new FileInputStream(classFile);
out = new ByteArrayOutputStream();
byte[] buff = new byte[1024];
int len;
while ((len = in.read(buff)) != -1) {
out.write(buff, 0, len);
}
return defineClass(className, out.toByteArray(), 0, out.size());
} catch (Exception e) {
e.printStackTrace();
}
}
}
return null;
}
}
自定义代理类
package com.drj.bj.proxy.drjproxy;
import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
public class DrjProxy {
public static final String ln = "\r\n";
public static Object newProxyInstance(DrjClassLoader classLoader, Class<?>[] interfaces, DrjInvocationHandler drjInvocationHandler) throws IllegalArgumentException, IOException, NoSuchMethodException, ClassNotFoundException, InvocationTargetException, InstantiationException, IllegalAccessException {
String src = generateSrc(interfaces);
String filePath = DrjProxy.class.getResource("").getPath();
File f = new File(filePath + "$Proxy0.java");
FileWriter fw = new FileWriter(f);
fw.write(src);
fw.flush();
fw.close();
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager manage = compiler.getStandardFileManager(null, null, null);
Iterable iterable = manage.getJavaFileObjects(f);
JavaCompiler.CompilationTask task = compiler.getTask(null, manage, null, null, null, iterable);
task.call();
manage.close();
Class proxyClass = classLoader.findClass("$Proxy0");
Constructor c = proxyClass.getConstructor(DrjInvocationHandler.class);
f.delete();
return c.newInstance(drjInvocationHandler);
}
private static String generateSrc(Class<?>[] interfaces) {
StringBuffer sb = new StringBuffer();
sb.append("package com.drj.bj.proxy.drjproxy;" + ln);
sb.append("import " + interfaces[0].getName() + ";" + ln);
sb.append("import java.lang.reflect.*;" + ln);
sb.append("public class $Proxy0 implements " + interfaces[0].getName() + "{" + ln);
sb.append("DrjInvocationHandler h;" + ln);
sb.append("public $Proxy0(DrjInvocationHandler h) { " + ln);
sb.append("this.h = h;");
sb.append("}" + ln);
for (Method m : interfaces[0].getMethods()) {
Class<?>[] params = m.getParameterTypes();
StringBuffer paramNames = new StringBuffer();
StringBuffer paramValues = new StringBuffer();
StringBuffer paramClasses = new StringBuffer();
for (int i = 0; i < params.length; i++) {
Class clazz = params[i];
String type = clazz.getName();
String paramName = toLowerFirstCase(clazz.getSimpleName());
paramNames.append(type + " " + paramName);
paramValues.append(paramName);
paramClasses.append(clazz.getName() + ".class");
if (i > 0 && i < params.length - 1) {
paramNames.append(",");
paramClasses.append(",");
paramValues.append(",");
}
}
sb.append("public " + m.getReturnType().getName() + " " + m.getName() + "(" + paramNames.toString() + ") {" + ln);
sb.append("try{" + ln);
sb.append("Method m = " + interfaces[0].getName() + ".class.getMethod(\"" + m.getName() + "\",new Class[]{" + paramClasses.toString() + "});" + ln);
sb.append((hasReturnValue(m.getReturnType()) ? "return " : "") + getCaseCode("this.h.invoke(this,m,new Object[]{" + paramValues + "})", m.getReturnType()) + ";" + ln);
sb.append("}catch(Error _ex) { }");
sb.append("catch(Throwable e){" + ln);
sb.append("throw new UndeclaredThrowableException(e);" + ln);
sb.append("}");
sb.append(getReturnEmptyCode(m.getReturnType()));
sb.append("}");
}
sb.append("}" + ln);
return sb.toString();
}
private static Map<Class, Class> mappings = new HashMap<Class, Class>();
static {
mappings.put(int.class, Integer.class);
}
private static String getReturnEmptyCode(Class<?> returnClass) {
if (mappings.containsKey(returnClass)) {
return "return 0;";
} else if (returnClass == void.class) {
return "";
} else {
return "return null;";
}
}
private static String getCaseCode(String code, Class<?> returnClass) {
if (mappings.containsKey(returnClass)) {
return "((" + mappings.get(returnClass).getName() + ")" + code + ")." + returnClass.getSimpleName() + "Value()";
}
return code;
}
private static boolean hasReturnValue(Class<?> clazz) {
return clazz != void.class;
}
private static String toLowerFirstCase(String src) {
char[] chars = src.toCharArray();
chars[0] += 32;
return String.valueOf(chars);
}
}
测试自定义动态代理
接口类
package com.drj.bj.proxy.drjproxy;
public interface DrjPerson {
void play();
}
实现类
package com.drj.bj.proxy.drjproxy;
import com.drj.bj.proxy.Person;
public class DrjPlayer implements DrjPerson {
@Override
public void play() {
System.out.println("我是自定義");
}
}
基于自定义代理类的实现动态代理
package com.drj.bj.proxy.drjproxy;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class DrjJdkPlay implements DrjInvocationHandler {
private Object target;
public Object getInstance(Object target) throws IOException, ClassNotFoundException, InvocationTargetException, NoSuchMethodException, InstantiationException, IllegalAccessException {
this.target = target;
return DrjProxy.newProxyInstance(new DrjClassLoader(), target.getClass().getInterfaces(), this);
}
@Override
public Object invoke(Object object, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException {
before();
Object invoke = method.invoke(this.target, args);
after();
return invoke;
}
private void before() {
System.out.println("孩子长大了开始玩游戏……");
}
private void after() {
System.out.println("成为职业玩家……");
}
public static void main(String[] args) throws IOException, ClassNotFoundException, InvocationTargetException, NoSuchMethodException, InstantiationException, IllegalAccessException {
DrjPerson instance = (DrjPerson) new DrjJdkPlay().getInstance(new DrjPlayer());
instance.play();
}
}
测试结果
孩子长大了开始玩游戏……
我是自定義
成为职业玩家……
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