自定义注解

可以用以上@interface来定义注解，基于java的元注解来创建

常用的元Annotation有@Retention 和@Target。@Retention注解可以简单理解为设置注解的生命周期，而@Target表示这个注解可以修饰哪些地方（比如方法、还是成员变量、还是包等等）

假设实现一个统一日志的功能，需要做哪些处理

1.自定义注解

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Log {
    String value() default "";

    /**
     * 是否启用
     *
     * @return
     */
    boolean enable() default true;

    LogActionType type() default LogActionType.SELECT;
}

2.记录日志的方法上增加注解

@GetMapping
@Log("查询聊天消息")
@ApiOperation("查询聊天消息")
@PreAuthorize("@el.check('imMessage:list')")
public ResponseEntity<Object> query(ImMessageQueryCriteria criteria, Pageable pageable){
    return new ResponseEntity<>(imMessageService.queryAll(criteria,pageable),HttpStatus.OK);
}

3.日志crud一套

4.日志aop

package com.xxx.aspect;

import com.xxx.service.LogService;
import lombok.extern.slf4j.Slf4j;
import com.xxx.domain.Log;
import com.xxx.utils.RequestHolder;
import com.xxx.utils.SecurityUtils;
import com.xxx.utils.StringUtils;
import com.xxx.utils.ThrowableUtil;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.stereotype.Component;
import javax.servlet.http.HttpServletRequest;

/**
 * @author
 * @date 2018-11-24
 */
@Component
@Aspect
@Slf4j
public class LogAspect {

    private final LogService logService;

    ThreadLocal<Long> currentTime = new ThreadLocal<>();

    public LogAspect(LogService logService) {
        this.logService = logService;
    }

    /**
     * 配置切入点
     */
    @Pointcut("@annotation(com.xxx.annotation.Log)")
    public void logPointcut() {
        // 该方法无方法体,主要为了让同类中其他方法使用此切入点
    }

    /**
     * 配置环绕通知,使用在方法logPointcut()上注册的切入点
     *
     * @param joinPoint join point for advice
     */
    @Around("logPointcut()")
    public Object logAround(ProceedingJoinPoint joinPoint) throws Throwable {
        Object result;
        currentTime.set(System.currentTimeMillis());
        result = joinPoint.proceed();
        Log log = new Log("INFO",System.currentTimeMillis() - currentTime.get());
        currentTime.remove();
        HttpServletRequest request = RequestHolder.getHttpServletRequest();
        logService.save(getUsername(), StringUtils.getBrowser(request), StringUtils.getIp(request),joinPoint, log);
        return result;
    }

    /**
     * 配置异常通知
     *
     * @param joinPoint join point for advice
     * @param e exception
     */
    @AfterThrowing(pointcut = "logPointcut()", throwing = "e")
    public void logAfterThrowing(JoinPoint joinPoint, Throwable e) {
        Long ct = currentTime.get();
        if(ct == null)ct = 0l;
        Log log = new Log("ERROR",System.currentTimeMillis() - ct);
        currentTime.remove();
        log.setExceptionDetail(ThrowableUtil.getStackTrace(e).getBytes());
        HttpServletRequest request = RequestHolder.getHttpServletRequest();
        logService.save(getUsername(), StringUtils.getBrowser(request), StringUtils.getIp(request), (ProceedingJoinPoint)joinPoint, log);
    }

    public String getUsername() {
        try {
            return SecurityUtils.getCurrentUsername();
        }catch (Exception e){
            return "";
        }
    }
}

以上就是一个基础的全局日志的实现

自定义注解的其他实现，我们可以用反射来获取到注解上面的标记的内容，这样，对于习惯使用代码来生成数据库的开发人员，也可以方便的写出一套代码生成器。