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190302-SpringBoot基础篇AOP之高级使用技能

前面一篇博文 190301-SpringBoot基础篇AOP之基本使用姿势小结介绍了aop的简单使用方式，在文章最后，抛出了几个问题待解决，本篇博文则将针对前面的问题，看下更多关于AOP的使用说明

I. 高级技能

1. 注解拦截方式

前面一文，主要介绍的是根据正则表达式来拦截对应的方法，接下来演示下如何通过注解的方式来拦截目标方法，实现也比较简单

首先创建注解

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface AnoDot {
}

接着在目标方法上添加注解，这里借助前面博文中工程进行说明，新建一个 com.git.hui.boot.aop.demo2.AnoDemoBean ，注意这个包路径，是不会被前文的 AnoAspect 定义的Advice拦截的，这里新建一个包路径的目的就是为了尽可能的减少干扰项

@Component
public class AnoDemoBean {
    @AnoDot
    public String genUUID(long time) {
        try {
            System.out.println("in genUUID before process!");
            return UUID.randomUUID() + "|" + time;
        } finally {
            System.out.println("in genUUID finally!");
        }
    }
}

接下来定义对应的advice, 直接在前面的 AnoAspect 中添加（不知道前文的也没关系，下面贴出相关的代码类，前文的类容与本节内容无关）

@Aspect
@Component
public class AnoAspect {
    @Before("@annotation(AnoDot)")
    public void anoBefore() {
        System.out.println("AnoAspect ");
    }
}

测试代码

@SpringBootApplication
public class Application {
    private AnoDemoBean anoDemoBean;

    public Application(AnoDemoBean anoDemoBean) {
        this.anoDemoBean = anoDemoBean;
        this.anoDemoBean();
    }

    private void anoDemoBean() {
        System.out.println(">>>>>>>" + anoDemoBean.genUUID(System.currentTimeMillis()));
    }
    
    public static void main(String[] args) {
        SpringApplication.run(Application.class);
    }
}

输出结果如下，在执行目标方法之前，会先执行before advice中的逻辑

AnoAspect 
in genUUID before process!
in genUUID finally!
>>>>>>>3a5d749d-d94c-4fc0-a7a3-12fd97f3e1fa|1551513443644

2. 多个advice拦截

一个方法执行时，如果有多个advice满足拦截规则，是所有的都会触发么？通过前面一篇博文知道，不同类型的advice是都可以拦截的，如果出现多个相同类型的advice呢？

在前面一篇博文的基础上进行操作，我们扩展下 com.git.hui.boot.aop.demo.DemoBean

@Component
public class DemoBean {
    @AnoDot
    public String genUUID(long time) {
        try {
            System.out.println("in genUUID before process!");
            return UUID.randomUUID() + "|" + time;
        } finally {
            System.out.println("in genUUID finally!");
        }
    }
}

对应的测试切面内容如

@Aspect
@Component
public class AnoAspect {

    @Before("execution(public * com.git.hui.boot.aop.demo.*.*(*))")
    public void doBefore(JoinPoint joinPoint) {
        System.out.println("do in Aspect before method called! args: " + JSON.toJSONString(joinPoint.getArgs()));
    }

    @Pointcut("execution(public * com.git.hui.boot.aop.demo.*.*(*))")
    public void point() {
    }

    @After("point()")
    public void doAfter(JoinPoint joinPoint) {
        System.out.println("do in Aspect after method called! args: " + JSON.toJSONString(joinPoint.getArgs()));
    }

    /**
     * 执行完毕之后，通过 args指定参数；通过 returning 指定返回的结果，要求返回值类型匹配
     *
     * @param time
     * @param result
     */
    @AfterReturning(value = "point() && args(time)", returning = "result")
    public void doAfterReturning(long time, String result) {
        System.out.println("do in Aspect after method return! args: " + time + " ans: " + result);
    }

    @Around("point()")
    public Object doAround(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("do in Aspect around ------ before");
        Object ans = joinPoint.proceed();
        System.out.println("do in Aspect around ------- over! ans: " + ans);
        return ans;
    }

    @Before("point()")
    public void sameBefore() {
        System.out.println("SameAspect");
    }

    @Before("@annotation(AnoDot)")
    public void anoBefore() {
        System.out.println("AnoAspect");
    }
}

测试代码如下

@SpringBootApplication
public class Application {
    private DemoBean demoBean;

    public Application(DemoBean demoBean) {
        this.demoBean = demoBean;
        this.demoBean();
    }

    private void demoBean() {
        System.out.println(">>>>> " + demoBean.genUUID(System.currentTimeMillis()));
    }

    public static void main(String[] args) {
        SpringApplication.run(Application.class);
    }
}

输出结果如下，所有的切面都执行了，也就是说，只要满足条件的advice，都会被拦截到

do in Aspect around ------ before
AnoAspect
do in Aspect before method called! args: [1551520547268]
SameAspect
in genUUID before process!
in genUUID finally!
do in Aspect around ------- over! ans: 5f6a5616-f558-4ac9-ba4b-b4360d7dc238|1551520547268
do in Aspect after method called! args: [1551520547268]
do in Aspect after method return! args: 1551520547268 ans: 5f6a5616-f558-4ac9-ba4b-b4360d7dc238|1551520547268
>>>>> 5f6a5616-f558-4ac9-ba4b-b4360d7dc238|1551520547268

3. 嵌套拦截

嵌套的方式有几种case，先看第一种

a. 调用方法不满足拦截规则，调用本类中其他满足拦截条件的方法

这里我们借助第一节中的bean来继续模拟, 在 AnoDemoBean 类中，新增一个方法

@Component
public class AnoDemoBean {

    public String randUUID(long time) {
        try {
            System.out.println("in randUUID start!");
            return genUUID(time);
        } finally {
            System.out.println("in randUUID finally!");
        }
    }

    @AnoDot
    public String genUUID(long time) {
        try {
            System.out.println("in genUUID before process!");
            return UUID.randomUUID() + "|" + time;
        } finally {
            System.out.println("in genUUID finally!");
        }
    }
}

对应的切面为

@Aspect
@Component
public class NetAspect {

    @Around("@annotation(AnoDot)")
    public Object doAround(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("In NetAspect doAround before!");
        Object ans = joinPoint.proceed();
        System.out.println("In NetAspect doAround over! ans: " + ans);
        return ans;
    }
}

然后测试case需要改为直接调用 AnoDemoBean#randUUID ，需要看这个方法内部调用的 genUUID 是否会被切面拦截住

@SpringBootApplication
public class Application {
    private AnoDemoBean anoDemoBean;

    public Application(AnoDemoBean anoDemoBean) {
        this.anoDemoBean = anoDemoBean;
        this.anoDemoBean();
    }

    private void anoDemoBean() {
        System.out.println(">>>>>>>" + anoDemoBean.randUUID(System.currentTimeMillis()));
    }

    public static void main(String[] args) {
        SpringApplication.run(Application.class);
    }
}

输出结果如下，没有切面的日志，表明这种场景下，不会被拦截

in randUUID start!
in genUUID before process!
in genUUID finally!
in randUUID finally!
>>>>>>>0c6a5ccf-30c0-4ac0-97f2-3dc063580f3d|1551522176035

b. 调用方法不满足拦截规则，调用其他类中满足拦截条件的方法

依然使用前面的例子进行说明，不过是稍稍改一下 AnoDemoBean ，调用第二节中的DemoBean的方法

DemoBean的代码如下

@AnoDot
public String genUUID(long time) {
    try {
        System.out.println("in DemoBean genUUID before process!");
        return UUID.randomUUID() + "|" + time;
    } finally {
        System.out.println("in DemoBean genUUID finally!");
    }
}

然后AnoDemoBean的代码如下

@Component
public class AnoDemoBean {
    @Autowired
    private DemoBean demoBean;

    public String randUUID(long time) {
        try {
            System.out.println("in AnoDemoBean randUUID start!");
            return genUUID(time) + "<<<>>>" + demoBean.genUUID(time);
        } finally {
            System.out.println("in AnoDemoBean randUUID finally!");
        }
    }

    @AnoDot
    public String genUUID(long time) {
        try {
            System.out.println("in AnoDemoBean genUUID before process!");
            return UUID.randomUUID() + "|" + time;
        } finally {
            System.out.println("in AnoDemoBean genUUID finally!");
        }
    }
}

测试代码和前面完全一致，接下来看下输出

in AnoDemoBean randUUID start!
in AnoDemoBean genUUID before process!
in AnoDemoBean genUUID finally!
### 上面三行为 anoDemoBean#randUUID方法调用 anoDemoBean#genUUID方法的输出结果，可以看到没有切面执行的日志输出
### 下面的为调用 demoBean#genUUID 方法，可以看到切面(NetAspect#doAround)执行的日志
In NetAspect doAround before!
in DemoBean genUUID before process!
in DemoBean genUUID finally!
In NetAspect doAround over! ans: f35b8878-fbd0-4840-8fbe-5fef8eda5e31|1551522532092
### 最后是收尾
in AnoDemoBean randUUID finally!
>>>>>>>e516a35f-b85a-4cbd-aae0-fa97cdecab47|1551522532092<<<>>>f35b8878-fbd0-4840-8fbe-5fef8eda5e31|1551522532092

从上面的日志分析中，可以明确看出对比，调用本类中，满足被拦截的方法，也不会走切面逻辑；调用其他类中的满足切面拦截的方法，会走切面逻辑

c. 调用方法满足切面拦截条件，又调用其他满足切面拦截条件的方法

这个和两个case有点像，不同的是直接调用的方法也满足被切面拦截的条件，我们主要关注点在于嵌套调用的方法，会不会进入切面逻辑，这里需要修改的地方就很少了，直接把 AnoDemoBean#randUUID 方法上添加注解，然后执行即可

@Component
public class AnoDemoBean {
    @Autowired
    private DemoBean demoBean;

    @AnoDot
    public String randUUID(long time) {
        try {
            System.out.println("in AnoDemoBean randUUID start!");
            return genUUID(time) + "<<<>>>" + demoBean.genUUID(time);
        } finally {
            System.out.println("in AnoDemoBean randUUID finally!");
        }
    }

    @AnoDot
    public String genUUID(long time) {
        try {
            System.out.println("in AnoDemoBean genUUID before process!");
            return UUID.randomUUID() + "|" + time;
        } finally {
            System.out.println("in AnoDemoBean genUUID finally!");
        }
    }
}

输出结果如下

## 最外层的切面拦截的是 AnoDemoBean#randUUID 方法的执行
In NetAspect doAround before!
in AnoDemoBean randUUID start!
in AnoDemoBean genUUID before process!
in AnoDemoBean genUUID finally!
### 从跟上面三行的输出，可以知道内部调用的 AnoDemoBean#genUUID 即便满足切面拦截规则，也不会再次走切面逻辑
### 下面4行，表明其他类的方法，如果满足切面拦截规则，会进入到切面逻辑
In NetAspect doAround before!
in DemoBean genUUID before process!
in DemoBean genUUID finally!
In NetAspect doAround over! ans: d9df7388-2ef8-4b1a-acb5-6639c47f36ca|1551522969801

in AnoDemoBean randUUID finally!
In NetAspect doAround over! ans: cf350bc2-9a9a-4ef6-b496-c913d297c960|1551522969801<<<>>>d9df7388-2ef8-4b1a-acb5-6639c47f36ca|1551522969801
>>>>>>>cf350bc2-9a9a-4ef6-b496-c913d297c960|1551522969801<<<>>>d9df7388-2ef8-4b1a-acb5-6639c47f36ca|1551522969801

从输出结果进行反推，一个结论是

执行的目标方法，如果调用了本类中一个满足切面规则的方法A时，在执行方法A的过程中，不会触发切面逻辑
执行的目标方法，如果调用其他类中一个满足切面规则的方法B时，在执行方法B的过程中，将会触发切面逻辑

4. AOP拦截方法作用域

前面测试的被拦截方法都是public，那么是否表明只有public方法才能被拦截呢？

从第三节基本可以看出，private方法首先淘汰出列，为啥？因为private方法正常来讲只能内部调用，而内部调用不会走切面逻辑；所以接下来需要关注的主要放在默认作用域和protected作用域

@Component
public class ScopeDemoBean {

    @AnoDot
    String defaultRandUUID(long time) {
        try {
            System.out.println(" in ScopeDemoBean defaultRandUUID before!");
            return UUID.randomUUID() + " | default | " + time;
        } finally {
            System.out.println(" in ScopeDemoBean defaultRandUUID finally!");
        }
    }

    @AnoDot
    protected String protectedRandUUID(long time) {
        try {
            System.out.println(" in ScopeDemoBean protectedRandUUID before!");
            return UUID.randomUUID() + " | protected | " + time;
        } finally {
            System.out.println(" in ScopeDemoBean protectedRandUUID finally!");
        }
    }

    @AnoDot
    private String privateRandUUID(long time) {
        try {
            System.out.println(" in ScopeDemoBean privateRandUUID before!");
            return UUID.randomUUID() + " | private | " + time;
        } finally {
            System.out.println(" in ScopeDemoBean privateRandUUID finally!");
        }
    }

}

我们不直接使用这个类里面的方法，借助前面的 AnoDemoBean ，下面给出了通过反射的方式来调用private方法的case

@Component
public class AnoDemoBean {
    @Autowired
    private ScopeDemoBean scopeDemoBean;

    public void scopeUUID(long time) {
        try {
            System.out.println("-------- default --------");
            String defaultAns = scopeDemoBean.defaultRandUUID(time);
            System.out.println("-------- default: " + defaultAns + " --------/n");


            System.out.println("-------- protected --------");
            String protectedAns = scopeDemoBean.protectedRandUUID(time);
            System.out.println("-------- protected: " + protectedAns + " --------/n");


            System.out.println("-------- private --------");
            Method method = ScopeDemoBean.class.getDeclaredMethod("privateRandUUID", long.class);
            method.setAccessible(true);
            String privateAns = (String) method.invoke(scopeDemoBean, time);
            System.out.println("-------- private: " + privateAns + " --------/n");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

测试case

@SpringBootApplication
public class Application {
    private AnoDemoBean anoDemoBean;

    public Application(AnoDemoBean anoDemoBean) {
        this.anoDemoBean = anoDemoBean;
        this.anoDemoBean();
    }

    private void anoDemoBean() {
        anoDemoBean.scopeUUID(System.currentTimeMillis());
    }

    public static void main(String[] args) {
        SpringApplication.run(Application.class);
    }
}

输出结果如下，从日志打印来看，protected和default方法的切面都走到了

-------- default --------
In NetAspect doAround before!
 in ScopeDemoBean defaultRandUUID before!
 in ScopeDemoBean defaultRandUUID finally!
In NetAspect doAround over! ans: 2ad7e509-c62c-4f25-b68f-eb5e0b53196d | default | 1551524311537
-------- default: 2ad7e509-c62c-4f25-b68f-eb5e0b53196d | default | 1551524311537 --------

-------- protected --------
In NetAspect doAround before!
 in ScopeDemoBean protectedRandUUID before!
 in ScopeDemoBean protectedRandUUID finally!
In NetAspect doAround over! ans: 9eb339f8-9e71-4321-ab83-a8953d1b8ff8 | protected | 1551524311537
-------- protected: 9eb339f8-9e71-4321-ab83-a8953d1b8ff8 | protected | 1551524311537 --------

-------- private --------
 in ScopeDemoBean privateRandUUID before!
 in ScopeDemoBean privateRandUUID finally!
-------- private: 1826afac-6eca-4dc3-8edc-b4ca7146ce28 | private | 1551524311537 --------