java学习

java学习

 

设计模式之模拟jdk的动态代理

jdk的动态代理模式的目标类和动态生成的代理类都要实现同一个接口。
public interface MoveAble {
void move();
}
public interface InvocationHandler {
public void invoke(Object o, Method m);
}
public class Tank1 implements MoveAble{
@Override
public void move() {
System.out.println("moving");
}
}
public class TimeHandler implements InvocationHandler{
private Object target;
public TimeHandler(Object target) {
super();
this.target = target;
}
@Override
public void invoke(Object o, Method m) {
long start = System.currentTimeMillis();
System.out.println("starttime:" + start);
System.out.println(o.getClass().getName());
try {
m.invoke(target);
} catch (Exception e) {
e.printStackTrace();
}
long end = System.currentTimeMillis();
System.out.println("time:" + (end-start));
}
}
public class Proxy {
public static Object newProxyInstance(Class infce, InvocationHandler invocationHandler) throws Exception { //JDK6 Complier API, CGLib, ASM
String methodStr = "";
String rt = "\r\n";
Method[] methods = infce.getMethods();
for(Method m : methods) {
Class<?> returnType = m.getReturnType();
methodStr += "@Override" + rt + 
"public  "+returnType+" " + m.getName() + "() {" + rt +
"    try {" + rt +
"    Method md = " + infce.getName() + ".class.getMethod(\"" + m.getName() + "\");" + rt +
"    h.invoke(this, md);" + rt +
"    }catch(Exception e) {e.printStackTrace();}" + rt +
"}";
}
String src = 
"package proxy.tank;" +  rt +
"import java.lang.reflect.Method;" + rt +
"public class $Proxy1 implements " + infce.getName() + "{" + rt +
"    public $Proxy1(InvocationHandler h) {" + rt +
"        this.h = h;" + rt +
"    }" + rt +
"    proxy.tank.InvocationHandler h;" + rt +
methodStr +
"}";
String fileName = 
"d:/src/proxy/tank/$Proxy1.java";
File f = new File(fileName);
FileWriter fw = new FileWriter(f);
fw.write(src);
fw.flush();
fw.close();
//compile
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);
Iterable units = fileMgr.getJavaFileObjects(fileName);
CompilationTask t = compiler.getTask(null, fileMgr, null, null, null, units);
t.call();
fileMgr.close();
//load into memory and create an instance
URL[] urls = new URL[] {new URL("file:/" + "d:/src/")};
URLClassLoader ul = new URLClassLoader(urls);
Class c = ul.loadClass("proxy.tank.$Proxy1");
System.out.println(c);
Constructor ctr = c.getConstructor(InvocationHandler.class);
Object m = ctr.newInstance(invocationHandler);
return m;
}
}
public class Client {
public static void main(String[] args) throws Exception {
Tank1 t = new Tank1();
InvocationHandler h = new TimeHandler(t);
MoveAble m = (MoveAble)Proxy.newProxyInstance(MoveAble.class, h);
m.move();
}
}

posted on 2017-09-14 15:35 杨军威 阅读(124) 评论(0)  编辑  收藏


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