Spring AOP Around Advice 實作 Exception 處理

緣由：專案內需要將Exception獨立抽出來處理，為了不影響原有的商業邏輯，並且讓code reuse
所以第一時間就想到要用AOP實作，順便回去練一下很久沒碰的Spring AOP，並複習一下觀念

問題：Exception處理

解決方式：Spring AOP Around Advice

好處：
1. 統一錯誤訊息，讓每個工程師各寫各的錯誤處理風格可以得到統一。
2. 讓其他人可以專注在商務邏輯
3. 程式看起來比較簡潔乾淨

基本上我不解釋觀念，因為網路上已經有很多很棒的解說了
我也還在學習，很多東西其實第一次看完全都不懂，很抽象，
但隨著時間、經驗的累積，又回去看了第二次第三次，就會越來越有感覺

AOP觀念與術語

spring-aop-diagram.jpg

In Spring AOP, 4 type of advices are supported :

• Before advice – Run before the method execution
• After returning advice – Run after the method returns a result
• After throwing advice – Run after the method throws an exception
• Around advice – Run around the method execution, combine all three advices above.

============================= 分隔線 =================================

我是使用 Around advice ，其實也就是把程式裡散落在各處的try catch集中至ExceptionAdvice統一處理。

build.gradle

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'maven'

compileJava.options.encoding = 'UTF-8'
def springVersion = "3.2.6.RELEASE"

dependencies {
    compile 'org.aspectj:aspectjweaver:1.7.1'
    compile 'org.slf4j:jcl-over-slf4j:1.7.1'
    compile 'org.slf4j:slf4j-log4j12:1.7.1'
    compile "org.springframework:spring-aop:$springVersion"
    compile "org.springframework:spring-context:$springVersion"
}

applicationContext.xml

com.test.aop.advice.ExceptionAdvice

public class ExceptionAdvice {
    private static Logger log = LoggerFactory.getLogger(ExceptionAdvice.class);

    public Object exceptionHandler(ProceedingJoinPoint proceedingJoinPoint) {
        Object value = null;

        try {
            value = proceedingJoinPoint.proceed();
        } catch (Throwable e) {
            log.info(proceedingJoinPoint.getSignature().getName() + " error");
            
            String errorMsg = "內部錯誤:" + e.getMessage();
            String errorCode = "500";
            
            Map resultJsonMap = new HashMap();
            resultJsonMap.put("successful", false);
            resultJsonMap.put("errorCode", errorCode);
            resultJsonMap.put("errorMsg", errorMsg );

            value = resultJsonMap;
            log.info(value.toString());
        }
        return value;
    }

com.test.service.TestService

public class TestService {
    private static ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
    
    public String runTest() {
        throw new IllegalArgumentException("這是測試");
    }

    public static void main(String[] args) {
        TestService ts = ac.getBean("testService", TestService.class);
        ts.runTest();
    }
}

參考資料

http://www.mkyong.com/spring/spring-aop-examples-advice/
http://www.journaldev.com/2583/spring-aop-example-tutorial-aspect-advice-pointcut-joinpoint-annotations-xml-configuration
http://www.springframework.org/schema/aop/spring-aop.xsd
http://www.mkyong.com/spring3/spring-aop-aspectj-in-xml-configuration-example/