详解使用Spring AOP和自定义注解进行参数检查

package com.lzumetal.ssm.paramcheck.annotation;

import java.lang.annotation.*;

/**
 * 标注在参数bean上，表示需要对该参数校验
 */
@Target({ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ValidParam {
  
  
}

package com.lzumetal.ssm.paramcheck.annotation;

import java.lang.annotation.*;

@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface NotNull {

  String msg() default "字段不能为空";
  
}

package com.lzumetal.ssm.paramcheck.annotation;

import java.lang.annotation.*;

@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface NotEmpty {

  String msg() default "字段不能为空";
  
}

package com.lzumetal.ssm.paramcheck.aspect;
import com.lzumetal.ssm.paramcheck.annotation.NotEmpty;
import com.lzumetal.ssm.paramcheck.annotation.NotNull;
import com.lzumetal.ssm.paramcheck.annotation.ValidParam;
import org.apache.commons.lang3.StringUtils;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.stereotype.Component;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.lang.reflect.Field;
import java.lang.reflect.Parameter;
import java.util.Arrays;
/**
 * 参数检查切面类
 */
@Aspect
@Component
public class ParamCheckAspect {

  @Before("execution(* com.lzumetal.ssm.paramcheck.controller.*.*(..))")
  public void paramCheck(JoinPoint joinPoint) throws Exception {
    //获取参数对象
    Object[] args = joinPoint.getArgs();
    //获取方法参数
    MethodSignature signature = (MethodSignature) joinPoint.getSignature();
    Parameter[] parameters = signature.getMethod().getParameters();
    for (int i = 0; i < parameters.length; i++) {
      Parameter parameter = parameters[i];
      //Java自带基本类型的参数（例如Integer、String）的处理方式
      if (isPrimite(parameter.getType())) {
        NotNull notNull = parameter.getAnnotation(NotNull.class);
        if (notNull != null && args[i] == null) {
          throw new RuntimeException(parameter.toString() + notNull.msg());
        }
        //TODO
        continue;
      }
      /*
       * 没有标注@ValidParam注解，或者是HttpServletRequest、HttpServletResponse、HttpSession时，都不做处理
      */
      if (parameter.getType().isAssignableFrom(HttpServletRequest.class) || parameter.getType().isAssignableFrom(HttpSession.class) ||
          parameter.getType().isAssignableFrom(HttpServletResponse.class) || parameter.getAnnotation(ValidParam.class) == null) {
        continue;
      }
      Class<?> paramClazz = parameter.getType();
      //获取类型所对应的参数对象，实际项目中Controller中的接口不会传两个相同的自定义类型的参数，所以此处直接使用findFirst()
      Object arg = Arrays.stream(args).filter(ar -> paramClazz.isAssignableFrom(ar.getClass())).findFirst().get();
      //得到参数的所有成员变量
      Field[] declaredFields = paramClazz.getDeclaredFields();
      for (Field field : declaredFields) {
        field.setAccessible(true);
        //校验标有@NotNull注解的字段
        NotNull notNull = field.getAnnotation(NotNull.class);
        if (notNull != null) {
          Object fieldValue = field.get(arg);
          if (fieldValue == null) {
            throw new RuntimeException(field.getName() + notNull.msg());
          }
        }
        //校验标有@NotEmpty注解的字段，NotEmpty只用在String类型上
        NotEmpty notEmpty = field.getAnnotation(NotEmpty.class);
        if (notEmpty != null) {
          if (!String.class.isAssignableFrom(field.getType())) {
            throw new RuntimeException("NotEmpty Annotation using in a wrong field class");
          }
          String fieldStr = (String) field.get(arg);
          if (StringUtils.isBlank(fieldStr)) {
            throw new RuntimeException(field.getName() + notEmpty.msg());
          }
        }
      }
    }
  }
  /**
   * 判断是否为基本类型：包括String
   * @param clazz clazz
   * @return true：是;   false：不是
   */
  private boolean isPrimite(Class<?> clazz){
    return clazz.isPrimitive() || clazz == String.class;
  }
}

package com.lzumetal.ssm.paramcheck.requestParam;
import com.lzumetal.ssm.paramcheck.annotation.NotEmpty;
import com.lzumetal.ssm.paramcheck.annotation.NotNull;
public class StudentParam {
  @NotNull
  private Integer id;
  private Integer age;
  @NotEmpty
  private String name;
  //get、set方法省略...
}

package com.lzumetal.ssm.paramcheck.controller;
import com.google.gson.Gson;
import com.lzumetal.ssm.paramcheck.annotation.NotNull;
import com.lzumetal.ssm.paramcheck.annotation.ValidParam;
import com.lzumetal.ssm.paramcheck.requestParam.StudentParam;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
@Controller
public class TestController {
  private static Gson gson = new Gson();
  @ResponseBody
  @RequestMapping(value = "/test", method = RequestMethod.POST)
  public StudentParam checkParam(@ValidParam StudentParam param, @NotNull Integer limit) {
    System.out.println(gson.toJson(param));
    System.out.println(limit);
    return param;
  }
}