本文内容纲要：《Java知识应用》模式实现Java 动态代理
动态代理说明：将你提供的接口改造成和你这个类有关的代理对象。
Java动态代理案例和原理：https://www.cnblogs.com/jssj/p/11771408.html
我们无法像JVM一样不需要生成Java文件直接生成字节码。我们模拟就通过手工生成java,然后编译成Class文件来实现。
模式案例：
package demo.knowledgepoints.invocationhandler;
public interface MyInvocationHandler {
public Object invoke();
}
package demo.knowledgepoints.invocationhandler;
public class MyInvocationHandlerImpl implements MyInvocationHandler {
@Override
public Object invoke() {
System.out.println("===== MyInvocationHandlerImpl =====");
return null;
}
}
package demo.knowledgepoints.invocationhandler;
public interface MyService {
public void query();
}
package demo.knowledgepoints.invocationhandler;
public class BinServvice implements MyService {
@Override
public void query() {
System.out.println("===== start BinServvice =======");
}
}
package demo.knowledgepoints.invocationhandler;
public class TaoService implements MyService {
@Override
public void query() {
System.out.println("========= start TaoService ========");
}
}
package demo.knowledgepoints.invocationhandler;
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.net.URL;
import java.net.URLClassLoader;
public class MyProxy {
public static void main(String[] args) {
try {
MyInvocationHandler myInvocationHandler = new MyInvocationHandlerImpl();
MyService myService = (MyService) MyProxy.getInstance(new BinServvice(),myInvocationHandler);
myService.query();
System.out.println("================================================");
myService = (MyService) MyProxy.getInstance(new TaoService(),myInvocationHandler);
myService.query();
} catch (Exception e) {
//
}
}
public static Object getInstance(Object target, MyInvocationHandler myInvocationHandler) throws IOException, ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
Class clazz = target.getClass().getInterfaces()[0];
Class myInvocationHandlerClazz = myInvocationHandler.getClass().getInterfaces()[0];
String interfaceName = clazz.getSimpleName(); //获取接口名称。
String content = "";
String line = "\n";//换行
String tab = "\t";//tab
/****组装一个类start ***/
String packageContent = "package demo.knowledgepoints.invocationhandler;" + line;
String importContent = "import " + clazz.getName() + ";" + line
+"import " + myInvocationHandlerClazz.getName() + ";" + line;
String clazzFirstLineContent = "public class $ProxyMy implements " + interfaceName + "{" + line;
String myInvocationHandlerName= myInvocationHandlerClazz.getSimpleName();
String filedContent = tab + "private " + interfaceName + " target;" + line
+ tab + "private " + myInvocationHandlerName + " myInvocationHandler;" + line;
String constructorContent = tab + "public $ProxyMy (" + interfaceName + " target,"+myInvocationHandlerName+" myInvocationHandler){" + line
+ tab + tab + "this.target =target;"
+ line + tab + tab + "this.myInvocationHandler = myInvocationHandler;"
+ line + tab + "}" + line;
String methodContent = "";
/**获取传入接口中的全部方法***/
Method[] methods = clazz.getDeclaredMethods();
/**循环组装接口中的各个方法**/
for (Method method : methods) {
//返回值类型
String returnTypeName = method.getReturnType().getSimpleName();
//方法名称
String methodName = method.getName();
// 参数类型的数组（int,String等）
Class args[] = method.getParameterTypes();
String argsContent = "";
String paramsContent = "";
int flag = 0;
for (Class arg : args) {
//String
String temp = arg.getSimpleName();
//String
//String p0
argsContent += temp + " p" + flag + ",";
//p0
paramsContent += "p" + flag + ",";
flag++;
}
if (argsContent.length() > 0) {
argsContent = argsContent.substring(0, argsContent.lastIndexOf(",") - 1);
paramsContent = paramsContent.substring(0, paramsContent.lastIndexOf(",") - 1);
}
methodContent += tab + "public " + returnTypeName + " " + methodName + "(" + argsContent + ") {" + line
+ tab + tab + "myInvocationHandler.invoke();" + line
+ tab + tab + "target." + methodName + "(" + paramsContent + ");" + line
+ tab + "}" + line;
}
content += packageContent + importContent + clazzFirstLineContent + filedContent + constructorContent + methodContent + "}";
/****组装一个类end ***/
/****将上述组装的类写入文件中***/
File file = new File("d:\\Study\\AcceleateWorld\\study\\MyProcedure\\src\\demo\\knowledgepoints\\invocationhandler\\$ProxyMy.java");
try {
if (!file.exists()) {
file.createNewFile();
}
FileWriter fw = new FileWriter(file);
fw.write(content);
fw.flush();
fw.close();
} catch (Exception e) {
}
/***使用JavaCompiler对象需要安装JDK，只有JAR无法使用**/
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);
Iterable units = fileMgr.getJavaFileObjects(file);
JavaCompiler.CompilationTask t = compiler.getTask(null, fileMgr, null, null, null, units);
t.call();
fileMgr.close();
/***将对象new出来读取到内存中***/
URL[] urls = new URL[]{new URL("file:d:\\Study\\AcceleateWorld\\study\\MyProcedure\\src\\\\")};
URLClassLoader urlClassLoader = new URLClassLoader(urls);
Class cls = urlClassLoader.loadClass("demo.knowledgepoints.invocationhandler.$ProxyMy");
Class[] classes = new Class[]{clazz,myInvocationHandlerClazz};
Constructor constructor = cls.getConstructor(classes);
Object o = constructor.newInstance(target,myInvocationHandler);
return o;
}
}
运行效果：
生成的代理java文件和Class文件：
本文内容总结：《Java知识应用》模式实现Java 动态代理
原文链接：https://www.cnblogs.com/jssj/p/12499086.html