深入探讨Java中动态代理技术的应用实例

原创ゝ一纸荒年。 2024-11-07 05:51 103阅读 0赞

Java中的动态代理是一种在运行时动态创建代理类和对象的机制。它允许开发者在不修改原有类代码的情况下，增加额外的功能。动态代理主要通过`java.lang.reflect.Proxy`类和`java.lang.reflect.InvocationHandler`接口实现。以下是动态代理技术的一些应用实例：

###1. 日志记录在方法执行前后添加日志记录，可以帮助开发者追踪方法的调用情况和执行结果。

```javaimport java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class LoggingProxy {
 private final Object target;

public LoggingProxy(Object target) {
 this.target = target;
 }

public static Object newProxyInstance(Object target) {
 return Proxy.newProxyInstance(
 target.getClass().getClassLoader(),
 target.getClass().getInterfaces(),
 new LoggingInvocationHandler(target));
 }

private static class LoggingInvocationHandler implements InvocationHandler {
 private final Object target;

public LoggingInvocationHandler(Object target) {
 this.target = target;
 }

@Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
 System.out.println("Before method: " + method.getName());
Object result = method.invoke(target, args);
 System.out.println("After method: " + method.getName());
 return result;
 }
 }
}
```###2.权限控制在方法执行前检查用户是否有权限执行该方法。

```javaimport java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class AccessControlProxy {
 private final Object target;

public AccessControlProxy(Object target) {
 this.target = target;
 }

private static class AccessControlInvocationHandler implements InvocationHandler {
 private final Object target;

public AccessControlInvocationHandler(Object target) {
 this.target = target;
 }

@Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (checkPermission(method)) {
 return method.invoke(target, args);
} else {
 throw new SecurityException("Access denied");
 }
 }

private boolean checkPermission(Method method) {
// 实现权限检查逻辑 return true;
 }
 }
}
```###3.事务管理在数据库操作前后添加事务的开启和关闭。

```javaimport java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import javax.sql.DataSource;

public class TransactionProxy {
 private final DataSource dataSource;

public TransactionProxy(DataSource dataSource) {
 this.dataSource = dataSource;
 }

public static Object newProxyInstance(DataSource dataSource) {
 return Proxy.newProxyInstance(
 dataSource.getClass().getClassLoader(),
 dataSource.getClass().getInterfaces(),
 new TransactionInvocationHandler(dataSource));
 }

private static class TransactionInvocationHandler implements InvocationHandler {
 private final DataSource dataSource;

public TransactionInvocationHandler(DataSource dataSource) {
 this.dataSource = dataSource;
 }

@Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
 try (Connection conn = dataSource.getConnection()) {
 conn.setAutoCommit(false);
Object result = method.invoke(dataSource, args);
 conn.commit();
 return result;
} catch (Exception e) {
//处理异常，回滚事务 }
 }
 }
}
```###4.性能监控监控方法的执行时间，用于性能分析。

```javaimport java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class PerformanceMonitorProxy {
 private final Object target;

public PerformanceMonitorProxy(Object target) {
 this.target = target;
 }

private static class PerformanceMonitorInvocationHandler implements InvocationHandler {
 private final Object target;

public PerformanceMonitorInvocationHandler(Object target) {
 this.target = target;
 }

@Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
 long startTime = System.currentTimeMillis();
Object result = method.invoke(target, args);
 long endTime = System.currentTimeMillis();
 System.out.println("Method " + method.getName() + " took " + (endTime - startTime) + "ms");
 return result;
 }
 }
}
```这些例子展示了动态代理在不同场景下的应用，包括日志记录、权限控制、事务管理和性能监控。动态代理提供了一种灵活的方式来增强和修改程序行为，而无需修改