31 Spring AOP通知实例 – Advice

2017-08-23 本文已影响84人笑Skr人啊

Spring AOP(面向方面编程)框架，用于在模块化方面的横切关注点。简单得说，它只是一个拦截器拦截一些过程，例如，当一个方法执行，Spring AOP 可以劫持一个执行的方法，在方法执行之前或之后添加额外的功能。

在Spring AOP中，有 4 种类型通知(advices)的支持：

1 通知(Advice)之前 - 该方法执行前运行
2 通知(Advice)返回之后 – 运行后，该方法返回一个结果
3 通知(Advice)抛出之后 – 运行方法抛出异常后，
4 环绕通知 – 环绕方法执行运行，结合以上这三个通知。

下面的例子显示Spring AOP 通知如何工作。

简单的 Spring 例子

创建一个简单的客户服务类及一个print方法作为演示。


package com.gp6.aop.advice;

public class CustomerService {
    private String name;
    private String url;

    public void setName(String name) {
        this.name = name;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void printName() {
        System.out.println("Customer name : " + this.name);
    }

    public void printURL() {
        System.out.println("Customer website : " + this.url);
    }

    public void printThrowException() {
        throw new IllegalArgumentException();
    }

}

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="customerService" class="com.gp6.aop.advice.CustomerService">
        <property name="name" value="Gp6" />
        <property name="url" value="http://www.jianshu.com/u/bdfd4b762426" />
    </bean>

</beans>


package com.gp6.aop.advice;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext("com/gp6/aop/advice/applicationContext.xml");

        CustomerService cust = (CustomerService) appContext.getBean("customerService");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (Exception e) {

        }

    }
}

一个简单的Spring项目用来注入(DI)bean和输出一些字符串。

Spring AOP 通知

现在，附加 Spring AOP 建议到上述的客户服务。

1. 之前通知

它会在方法执行之前执行。创建一个实现 MethodBeforeAdvice 接口的类。

package com.gp6.aop.advice.before;

import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;

public class HijackBeforeMethod implements MethodBeforeAdvice{
    @Override
    public void before(Method method, Object[] args, Object target)
        throws Throwable {
            System.out.println("HijackBeforeMethod : Before method!");
    }
}

在 bean 配置文件(applicationContext.xml)，创建一个 bean 的 HijackBeforeMethod 类，并命名为“customerServiceProxy” 作为一个新的代理对象。

‘target’ – 定义你想拦截的bean。
‘interceptorNames’ – 定义要应用这个代理/目标对象的类(通知)。


package com.gp6.aop.advice.before;

public class CustomerService {
    private String name;
    private String url;

    public void setName(String name) {
        this.name = name;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void printName() {
        System.out.println("Customer name : " + this.name);
    }

    public void printURL() {
        System.out.println("Customer website : " + this.url);
    }

    public void printThrowException() {
        throw new IllegalArgumentException();
    }

}

package com.gp6.aop.advice.before;

import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;

public class HijackBeforeMethod implements MethodBeforeAdvice{
    @Override
    public void before(Method method, Object[] args, Object target)
        throws Throwable {
            System.out.println("HijackBeforeMethod : Before method!");
    }
}

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="customerService" class="com.gp6.aop.advice.before.CustomerService">
        <property name="name" value="Gp6" />
        <property name="url" value="http://www.jianshu.com/u/bdfd4b762426" />
    </bean>

    <bean id="hijackBeforeMethodBean" class="com.gp6.aop.advice.before.HijackBeforeMethod" />

    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackBeforeMethodBean</value>
            </list>
        </property>
    </bean>
</beans>

package com.gp6.aop.advice.before;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext("com/gp6/aop/advice/before/applicationContext.xml");

        CustomerService cust = (CustomerService) appContext.getBean("customerServiceProxy");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (Exception e) {

        }

    }
}

输出结果

*************************
HijackBeforeMethod : Before method!
Customer name : Gp6
*************************
HijackBeforeMethod : Before method!
Customer website : http://www.jianshu.com/u/bdfd4b762426
*************************
HijackBeforeMethod : Before method!

它将运行 HijackBeforeMethod 的 before() 方法，在每个 CustomerService 的方法之前执行。

2.返回后通知

该方法返回一个结果之后它将执行。创建一个实现AfterReturningAdvice接口的类。

package com.gp6.aop.advice.after;

import java.lang.reflect.Method;

import org.springframework.aop.AfterReturningAdvice;

public class HijackAfterMethod implements AfterReturningAdvice{
    @Override
    public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
            System.out.println("HijackAfterMethod : After method hijacked!");
    }
}


package com.gp6.aop.advice.after;

public class CustomerService {
    private String name;
    private String url;

    public void setName(String name) {
        this.name = name;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void printName() {
        System.out.println("Customer name : " + this.name);
    }

    public void printURL() {
        System.out.println("Customer website : " + this.url);
    }

    public void printThrowException() {
        throw new IllegalArgumentException();
    }

}

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="customerService" class="com.gp6.aop.advice.after.CustomerService">
        <property name="name" value="Gp6" />
        <property name="url" value="http://www.jianshu.com/u/bdfd4b762426" />
    </bean>

    <bean id="hijackAfterMethodBean" class="com.gp6.aop.advice.after.HijackAfterMethod" />

    <bean id="customerServiceProxy" 
                class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackAfterMethodBean</value>
            </list>
        </property>
    </bean>
</beans>

package com.gp6.aop.advice.after;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext("com/gp6/aop/advice/after/applicationContext.xml");

        CustomerService cust = (CustomerService) appContext.getBean("customerServiceProxy");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (Exception e) {

        }

    }
}

再次运行，输出

*************************
Customer name : Gp6
HijackAfterMethod : After method hijacked!
*************************
Customer website : http://www.jianshu.com/u/bdfd4b762426
HijackAfterMethod : After method hijacked!
*************************

它将运行 HijackAfterMethod 的 afterReturning()方法，在每次 CustomerService 方法返回结果之后。

3.抛出后通知

它将在执行方法抛出一个异常后。创建一个实现ThrowsAdvice接口的类，并创建一个afterThrowing方法拦截抛出：IllegalArgumentException异常。

package com.gp6.aop.advice.afterThrow;

import org.springframework.aop.ThrowsAdvice;

public class HijackThrowException implements ThrowsAdvice {
    public void afterThrowing(IllegalArgumentException e) throws Throwable {
        System.out.println("HijackThrowException : Throw exception hijacked!");
    }
}


<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="customerService" class="com.gp6.aop.advice.afterThrow.CustomerService">
        <property name="name" value="Gp6" />
        <property name="url" value="http://www.jianshu.com/u/bdfd4b762426" />
    </bean>

    <bean id="hijackThrowExceptionBean" class="com.gp6.aop.advice.afterThrow.HijackThrowException" />

    <bean id="customerServiceProxy" 
                 class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackThrowExceptionBean</value>
            </list>
        </property>
    </bean>
</beans>

package com.gp6.aop.advice.afterThrow;

public class CustomerService {
    private String name;
    private String url;

    public void setName(String name) {
        this.name = name;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void printName() {
        System.out.println("Customer name : " + this.name);
    }

    public void printURL() {
        System.out.println("Customer website : " + this.url);
    }

    public void printThrowException() {
        throw new IllegalArgumentException();
    }

}

package com.gp6.aop.advice.afterThrow;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext("com/gp6/aop/advice/afterThrow/applicationContext.xml");

        CustomerService cust = (CustomerService) appContext.getBean("customerServiceProxy");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            System.out.println("扎心不");
            cust.printThrowException();
        } catch (Exception e) {

        }

    }
}

输出:

*************************
Customer name : Gp6
*************************
Customer website : http://www.jianshu.com/u/bdfd4b762426
*************************
扎心不
HijackThrowException : Throw exception hijacked!

它将运行 HijackThrowException 的 afterThrowing()方法，如果 CustomerService 的方法抛出异常。

4.环绕通知

它结合了上面的三个通知，在方法执行过程中执行。创建一个实现了MethodInterceptor接口的类。必须调用“methodInvocation.proceed();” 继续在原来的方法执行，否则原来的方法将不会执行。

package com.gp6.aop.advice.around;

import java.util.Arrays;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

public class HijackAroundMethod implements MethodInterceptor {
    @Override
    public Object invoke(MethodInvocation methodInvocation) throws Throwable {

        System.out.println("Method name : "
                + methodInvocation.getMethod().getName());
        
        System.out.println("Method arguments : "
                + Arrays.toString(methodInvocation.getArguments()));

        // same with MethodBeforeAdvice
        System.out.println("HijackAroundMethod : Before method hijacked!");

        try {
            // proceed to original method call
            Object result = methodInvocation.proceed();

            // same with AfterReturningAdvice
            System.out.println("HijackAroundMethod : Before after hijacked!");

            return result;

        } catch (IllegalArgumentException e) {
            // same with ThrowsAdvice
            System.out.println("HijackAroundMethod : Throw exception hijacked!");
            throw e;
        }
    }
}


<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="customerService" class="com.gp6.aop.advice.around.CustomerService">
        <property name="name" value="Gp6" />
        <property name="url" value="http://www.jianshu.com/u/bdfd4b762426" />
    </bean>

    <bean id="hijackAroundMethodBean" class="com.gp6.aop.advice.around.HijackAroundMethod" />

    <bean id="customerServiceProxy" 
                class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackAroundMethodBean</value>
            </list>
        </property>
    </bean>
</beans>

package com.gp6.aop.advice.around;

public class CustomerService {
    private String name;
    private String url;

    public void setName(String name) {
        this.name = name;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void printName() {
        System.out.println("Customer name : " + this.name);
    }

    public void printURL() {
        System.out.println("Customer website : " + this.url);
    }

    public void printThrowException() {
        throw new IllegalArgumentException();
    }

}


package com.gp6.aop.advice.around;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext("com/gp6/aop/advice/around/applicationContext.xml");

        CustomerService cust = (CustomerService) appContext.getBean("customerServiceProxy");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (Exception e) {

        }

    }
}

它将运行HijackAroundMethod 的 invoke()方法，在每一个 CustomerService 方法执行后。

总结

大部分的 Spring 开发者都只是实现了“环绕通知”，因为它可以对所有通知类型，但更好的做法应该是选择最合适的通知类型来满足要求。

切入点

在这个例子中，在一客户服务类中的所有方法都自动拦截(通知)。但在大多数情况下，可能需要使用切入点和Advisor通过它的方法名拦截它的方法。