java动态代理

1.JDK代理

    动态的由java提供的api在内存中构建字节码类对象完成的动态代理.

    使用JDK代理方式动态创建对象时,对象需要声明接口并且实现接口;

    1.1声明接口:

package yzr.dyn_jdk;public interface IPerson {void SayHello();}

   1.2 声明对象,并且实现接口:

package yzr.dyn_jdk;public class PersonImpl implements IPerson {private String name;@Overridepublic void SayHello() {System.out.println("Hello "+this.name);}public PersonImpl(){}public PersonImpl(String name){this.name=name;}}

    1.3实现自己的InvocationHandler类

package yzr.dyn_jdk;import java.lang.reflect.InvocationHandler;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;public class MyInvocationHandler implements InvocationHandler {private Object target;public MyInvocationHandler(){super();}public MyInvocationHandler(Object target){super();this.target=target;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args){Object Result=null;try {Result=method.invoke(target, args);} catch (Exception e) {e.printStackTrace();} return Result;}}

     1.4得到代理对象并且调用

package yzr.dyn_jdk;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Proxy;  public class TestUnit {public static void main(String[] args) {IPerson LYF=new PersonImpl("yzr");InvocationHandler handler=new MyInvocationHandler(LYF);IPerson LYFProxy = (IPerson)Proxy.newProxyInstance(LYF.getClass().getClassLoader(),  LYF.getClass().getInterfaces(),handler); LYFProxy.SayHello();}}

      使用JDK代理的方式动态创建对象时,和使用new关键字(或者反射)创建对象的不同在于,调用对象的方法的时候,可以加入额外的逻辑代码,比如:

        @Overridepublic Object invoke(Object proxy, Method method, Object[] args){Object Result=null;try {System.out.println("调用方法之前:");Result=method.invoke(target, args);System.out.println("调用方法之后:");} catch (Exception e) {e.printStackTrace();} return Result;}

      但是不方便的地方是使用JDK代理这方式要求声明接口,实现接口的对象才能被动态代理生成,所以下面使用cglib代理动态创建对象:

2.cglib代理

     需要三个jar包: asm-3.3.1.jar     cglib-2.2.jar     cglib-nodep-2.2.jar

     2.1声明对象

package yzr.dyn_cglib;public class PersonImpl {private String name;public void SayHello() {System.out.println("Hello "+this.name);}public PersonImpl(){}public PersonImpl(String name){this.name=name;}}

     2.2 实现MethodInterceptor接口

package yzr.dyn_cglib;import java.lang.reflect.Method;import net.sf.cglib.proxy.MethodInterceptor;import net.sf.cglib.proxy.MethodProxy;public class CglibProxy implements MethodInterceptor {@Overridepublic Object intercept(Object arg0, Method arg1, Object[] arg2,MethodProxy arg3) throws Throwable {System.out.println(arg1.getName());  System.out.println("调用方法之前");Object result=arg3.invokeSuper(arg0, arg2);System.out.println("调用方法之之后");return result;}}

     2.3动态获取对象

package yzr.dyn_cglib;import yzr.dyn_jdk.PersonImpl;import net.sf.cglib.proxy.Enhancer;public class CglibUnit {public static void main(String[] args) {CglibProxy proxy=new CglibProxy();Enhancer enhancer = new Enhancer();  enhancer.setSuperclass(PersonImpl.class);      enhancer.setCallback(proxy);      PersonImpl per = (PersonImpl)enhancer.create();          per.SayHello();}}

  像这样的方式就可以不要求一定需要声明接口就可以动态代理,但是不管是JDK代理或者CgLib代理,都需要事先声明PersonImpl实体类,就是说被动态创建的对象都需要声明好,假如说如果不想手动声明这样的一个实体类(被动态创建的对象),又或者说即使是声明了类似于PersonImpl这样的实体对象,但需要能够动态的为它新增一些新的属性并且赋值,这些想法都可以实现.,下面说一下该怎么做:

3.动态代理

   一个动态Bean,读取属性文件内容作为被创建对象的属性,当然你也可以选择不使用属性文件,直接写在代码上也可以;

   

package yzr.dynamiceBean;import java.util.Iterator;import java.util.Map;import java.util.Set;import net.sf.cglib.beans.BeanGenerator;import net.sf.cglib.beans.BeanMap;public class DynamicBean { private  Object object = null;//动态生成的类 private  BeanMap beanMap = null;//存放属性名称以及属性的类型 public DynamicBean() {  super(); }  public DynamicBean(Map propertyMap) { this.object = generateBean(propertyMap); this.beanMap = BeanMap.create(this.object); } public void setValue(Object property, Object value) {  beanMap.put(property, value);         } public Object getValue(String property) {  return beanMap.get(property); } public Object getObject() {  return this.object; } private Object generateBean(Map propertyMap) {  BeanGenerator generator = new BeanGenerator();  Set keySet = propertyMap.keySet();  for (Iterator i = keySet.iterator(); i.hasNext();) {    String key = (String) i.next();    generator.addProperty(key, (Class) propertyMap.get(key));  }  return generator.create();}}

package yzr.dynamiceBean;import java.beans.BeanInfo;import java.beans.Introspector;import java.beans.PropertyDescriptor;import java.io.InputStream;import java.lang.reflect.Field;import java.lang.reflect.Method;import java.util.HashMap;import java.util.Iterator;import java.util.Properties;import java.util.Set;public class ClassUtil {public Object dynamicClass(Object object) throws Exception {HashMap returnMap = new HashMap();HashMap typeMap = new HashMap();// 读取配置文件Properties prop = new Properties();String sourcepackage = object.getClass().getName();String classname = sourcepackage.substring(sourcepackage.lastIndexOf(".") + 1);InputStream in = ClassUtil.class.getResourceAsStream("/Dynamic.properties");prop.load(in);Set<String> keylist = prop.stringPropertyNames();Class type = object.getClass();BeanInfo beanInfo = Introspector.getBeanInfo(type);PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();//添加自身属性for (int i = 0; i < propertyDescriptors.length; i++) {PropertyDescriptor descriptor = propertyDescriptors[i];String propertyName = descriptor.getName();if (!propertyName.equals("class")) {Method readMethod = descriptor.getReadMethod();Object result = readMethod.invoke(object, new Object[0]);if (result != null) {returnMap.put(propertyName, result);} else {returnMap.put(propertyName, "");}typeMap.put(propertyName, descriptor.getPropertyType());}}// 加载配置文件中的属性Iterator<String> iterator = keylist.iterator();while (iterator.hasNext()) {String key = iterator.next();returnMap.put(key, prop.getProperty(key));typeMap.put(key, Class.forName("java.lang.String"));}// map转换成实体对象DynamicBean bean = new DynamicBean(typeMap);// 赋值Set keys = typeMap.keySet();for (Iterator it = keys.iterator(); it.hasNext();) {String key=it.next().toString();bean.setValue(key, returnMap.get(key));}Object obj = bean.getObject();return obj;}public static void main(String[] args) throws Exception {Object object = new ClassUtil().dynamicClass(new Object());Class c = object.getClass();Method[] methods = c.getDeclaredMethods();// 得到方法Field[] fs = c.getDeclaredFields();for (int i = 0; i < fs.length; i++) {Field f = fs[i];f.setAccessible(true); // 设置些属性是可以访问的Object val = f.get(object);// 得到此属性的值String type = f.getType().toString();// 得到此属性的类型System.out.println("type=" + type + "\t name:" + f.getName()+ "\t value = " + val);}}}

属性文件Dynamic.properties:

name=YZR;

运行结果:

被动态创建对象中的属性会带有$cglib_prop前缀;

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