一、java中的反射
1.通过反射加载类的属性和方法实例代码:
Class clazz = StudentExam.class;
StudentExam studentExam = clazz.newInstance();
System.err.println(studentExam);
System.out.println(clazz);
// Field field = clazz.getField("id"); // 通过属性调用运行时类的指定属性：属性是public类型
Field field = clazz.getDeclaredField("id"); // 属性是非public 类型
Field[] fields = clazz.getDeclaredFields(); // 获取运行时类本身(父类不行)所有声明的属性，父类使用clazz.getFields();
for (Field field2 : fields) {
int i = field2.getModifiers();
String type = Modifier.toString(i);// 获取字段属性的数据类型
System.out.println(type);
}
field.setAccessible(true);
field.set(studentExam, 11);
System.err.println(studentExam.getId());
// 通过反射调用运行时类的指定方法
Method method = clazz.getMethod("setId", Integer.class);
method.invoke(studentExam, 123); // 调用运行时类的指定方法
Method[] methods = clazz.getMethods(); // 获取所有运行时类及其父类中所有声明为public的方法
Method[] methods2 = clazz.getDeclaredMethods();// 获取运行时类本身类中声明的方法
for (Method method2 : methods) {
System.out.println(method2.getName());
}
// * 通过对象的getClass()方法获取对象的运行时类，
Exam exam = new Exam();
Class clazzExam = exam.getClass();
2.类加载器ClassLoader
public void classLoader() throws IOException {
//方法一、从当前工程下加载
ClassLoader loader = this.getClass().getClassLoader();
// 路径是包下写：com\able\onlineExam\resources\config.properties
InputStream inStream = loader.getResourceAsStream("config.properties");
// 方法二、从指定的路径下加载文件
// FileInputStream fileInputStream = new FileInputStream(new File("config.properties"));
Properties properties = new Properties();
properties.load(inStream);
// properties.load(fileInputStream);
String prop = properties.getProperty("domain");
System.out.println(prop);
}
3.动态代理
静态代理:代理类和目标对象的类型都是在编译期间确定下来，不利于程序的扩展。同时每个代理类只能为一个接口服务，这样一来程序开发中必然产生过多的代理。
动态代理:客户通过代理类来调用其他对象的方法，并且是在程序运行时，根据需要动态创建目标类的代理对象。
代理设计模式的原理：
使用一个代理将对象包装起来，然后用该代理对象取代原始对象，任何对原始对象的调用都要通过代理，代理对象决定的那个是否以及何时将方法调用
package com.test.junit;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class ProxyTest {
public static void main(String[] args) {
RealSubject realSubject = new RealSubject();
MyInvocationHandler myInvocationHandler = new MyInvocationHandler();
Object object = myInvocationHandler.bind(realSubject);
Subject subject = (Subject) object;
subject.action();
}
}
// 动态代理的使用
interface Subject{
void action();
}
// 被代理类
class RealSubject implements Subject{
@Override
public void action() {
System.out.println("我是被代理类，记得执行我哦。。。。");
}
}
class MyInvocationHandler implements InvocationHandler{
Object object;// 实现了接口的被代理类的对象的声明
public Object bind(Object object){
this.object = object;
return Proxy.newProxyInstance(object.getClass().getClassLoader(), object.getClass().getInterfaces(), this);
}
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
Object returnObject = method.invoke(object, args);
return returnObject;
}
}
4.动态代理与AOP
示例一、
package com.atguigu.spring.aop;
public interface ArithmeticCalculator {
int add(int i, int j);
int sub(int i, int j);
int mul(int i, int j);
int div(int i, int j);
}
package com.atguigu.spring.aop;
import org.springframework.stereotype.Component;
@Component("arithmeticCalculator")
public class ArithmeticCalculatorImpl implements ArithmeticCalculator {
@Override
public int add(int i, int j) {
int result = i + j;
return result;
}
@Override
public int sub(int i, int j) {
int result = i - j;
return result;
}
@Override
public int mul(int i, int j) {
int result = i * j;
return result;
}
@Override
public int div(int i, int j) {
int result = i / j;
return result;
}
}
package com.atguigu.spring.aop;
public class ArithmeticCalculatorLoggingImpl implements ArithmeticCalculator {
@Override
public int add(int i, int j) {
System.out.println("The method add begins with [" + i + "," + j + "]");
int result = i + j;
System.out.println("The method add ends with " + result);
return result;
}
@Override
public int sub(int i, int j) {
System.out.println("The method sub begins with [" + i + "," + j + "]");
int result = i - j;
System.out.println("The method sub ends with " + result);
return result;
}
@Override
public int mul(int i, int j) {
System.out.println("The method mul begins with [" + i + "," + j + "]");
int result = i * j;
System.out.println("The method mul ends with " + result);
return result;
}
@Override
public int div(int i, int j) {
System.out.println("The method div begins with [" + i + "," + j + "]");
int result = i / j;
System.out.println("The method div ends with " + result);
return result;
}
}
package com.atguigu.spring.aop;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
public class ArithmeticCalculatorLoggingProxy {
//要代理的对象
private ArithmeticCalculator target;
public ArithmeticCalculatorLoggingProxy(ArithmeticCalculator target) {
super();
this.target = target;
}
//返回代理对象
public ArithmeticCalculator getLoggingProxy(){
ArithmeticCalculator proxy = null;
// 代理对象有哪一个类加载器负责加载
ClassLoader loader = target.getClass().getClassLoader();
// 代理对象的类型，即其中有哪些方法
Class [] interfaces = new Class[]{ArithmeticCalculator.class};
// 当调用代理对象的其中方法时，执行下面的代码
InvocationHandler h = new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
// 在方法内部不会直接调用proxy对象的某个方法，proxy.toString()会造成死循环调用invoke方法
String methodName = method.getName();
//打印日志
System.out.println("[before] The method " + methodName + " begins with " + Arrays.asList(args));
//调用目标方法
Object result = null;
try {
//前置通知
result = method.invoke(target, args);
//返回通知, 可以访问到方法的返回值
} catch (NullPointerException e) {
e.printStackTrace();
//异常通知, 可以访问到方法出现的异常
}
//后置通知. 因为方法可以能会出异常, 所以访问不到方法的返回值
//打印日志
System.out.println("[after] The method ends with " + result);
return result;
}
};
proxy = (ArithmeticCalculator) Proxy.newProxyInstance(loader, interfaces, h);
return proxy;
}
}
package com.atguigu.spring.aop;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
public static void main(String[] args) {
// ArithmeticCalculator arithmeticCalculator = new ArithmeticCalculatorImpl();
ArithmeticCalculator arithmeticCalculator = new ArithmeticCalculatorLoggingImpl();
arithmeticCalculator = new ArithmeticCalculatorLoggingProxy(arithmeticCalculator).getLoggingProxy();
int result = arithmeticCalculator.add(11, 12);
System.out.println("result:" + result);
result = arithmeticCalculator.div(21, 3);
System.out.println("result:" + result);
}
}
示例二、
package com.test.junit;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class ProxyTest {
public static void main(String[] args) {
RealSubject realSubject = new RealSubject();
MyInvocationHandler myInvocationHandler = new MyInvocationHandler();
Object object = myInvocationHandler.bind(realSubject);
Subject subject = (Subject) object;
subject.action();
}
}
// 动态代理的使用
interface Subject{
void action();
}
// 被代理类
class RealSubject implements Subject{
@Override
public void action() {
System.out.println("我是被代理类，记得执行我哦。。。。");
}
}
class MyInvocationHandler implements InvocationHandler{
Object object;// 实现了接口的被代理类的对象的声明
public Object bind(Object object){
this.object = object;
return Proxy.newProxyInstance(object.getClass().getClassLoader(), object.getClass().getInterfaces(), this);
}
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
Object returnObject = method.invoke(object, args);
return returnObject;
}
}
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