Java自定义注解源码+原理解释（使用Java自定义注解校验bean传入参数合法性）

Java自定义注解源码+原理解释（使用Java自定义注解校验bean传入参数合法性）

前言：由于前段时间忙于写接口，在接口中需要做很多的参数校验，本着简洁、高效的原则，便写了这个小工具供自己使用（内容为缩减版，具体业务可自行扩展）

思路：使用Java反射机制，读取实体类属性头部注解，通过get方法获取参数值进行校验，如果为空则进行异常抛出。

CheckNull.java 类

package com.seesun2012.common.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 自定义注解：校验非空字段
 *
 * @author seesun2012@163.com
 *
 */
@Documented
@Inherited
// 接口、类、枚举、注解
@Target(ElementType.FIELD)
//只是在运行时通过反射机制来获取注解，然后自己写相应逻辑（所谓注解解析器）
@Retention(RetentionPolicy.RUNTIME)
public @interface CheckNull {
	String message();
}

Userregister.java 类

package com.seesun2012.common.entity;

import java.io.Serializable;

import com.seesun2012.common.annotation.CheckNull;

/**
 * 用户注册实体类
 *
 * @author seesun2012@163.com
 *
 */
public class Userregister implements Serializable{

	private static final long serialVersionUID = 1L;

	//自定义注解
	@CheckNull(message="用户名不能为空")
	private String userAccount;
	//自定义注解
	@CheckNull(message="密码不能为空")
	private String passWord;

	public String getUserAccount() { return userAccount; }
	public void setUserAccount(String userAccount) { this.userAccount = userAccount; }
	public String getPassWord() { return passWord; }
	public void setPassWord(String passWord) { this.passWord = passWord; }

	@Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(getClass().getSimpleName());
        sb.append(" [");
        sb.append("Hash = ").append(hashCode());
        sb.append(", userAccount=").append(userAccount);
        sb.append(", passWord=").append(passWord);
        sb.append(", serialVersionUID=").append(serialVersionUID);
        sb.append("]");
        return sb.toString();
    }
}

CommonUtils.java 类

package com.seesun2012.common.utils;

import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.List;

import com.seesun2012.common.annotation.CheckNull;
import com.seesun2012.common.exception.CustBusinessException;

/**
 * 公共工具类
 *
 * @author seesun2012@163.com
 *
 */
public class CommonUtils{

	/**
     * 通过反射来获取javaBean上的注解信息，判断属性值信息，然后通过注解元数据来返回
     */
	public static <T> boolean doValidator(T clas){
		Class<?> clazz = clas.getClass();
		Field[] fields = clazz.getDeclaredFields();
		for (Field field : fields) {
			CheckNull checkNull = field.getDeclaredAnnotation(CheckNull.class);
			if (null!=checkNull) {
				Object value = getValue(clas, field.getName());
				if (!notNull(value)) {
					throwExcpetion(checkNull.message());
				}
			}
		}
		return true;
	}

	/**
	 * 获取当前fieldName对应的值
	 *
	 * @param clas		对应的bean对象
	 * @param fieldName	bean中对应的属性名称
	 * @return
	 */
	public static <T> Object getValue(T clas,String fieldName){
		Object value = null;
		try {
			BeanInfo beanInfo = Introspector.getBeanInfo(clas.getClass());
			PropertyDescriptor[] props = beanInfo.getPropertyDescriptors();
			for (PropertyDescriptor property : props) {
				if (fieldName.equals(property.getName())) {
					Method method = property.getReadMethod();
					value = method.invoke(clas, new Object[]{});
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		return value;
	}

	/**
	 * 非空校验
	 *
	 * @param value
	 * @return
	 */
	public static boolean notNull(Object value){
		if(null==value){
            return false;
        }
        if(value instanceof String && isEmpty((String)value)){
            return false;
        }
        if(value instanceof List && isEmpty((List<?>)value)){
            return false;
        }
        return null!=value;
	}

	public static boolean isEmpty(String str){
        return null==str || str.isEmpty();
    }
    public static boolean isEmpty(List<?> list){
        return null==list || list.isEmpty();
    }

	private static void throwExcpetion(String msg) {
		if(null!=msg){
            throw new CustBusinessException(msg);
        }
	}

}

Result.java 类

package com.seesun2012.common.entity;

import java.io.Serializable;
import java.util.HashMap;

public class Result extends HashMap<String, Object> implements Serializable {

	private static final long serialVersionUID = 1L;

	public static final Result SUCCEED = new Result(0, "操作成功");

	public Result(int status, String massage) {
		super();
		this.put("status", status).put("message", massage);
	}

	public Result put(String key, Object value) {
		super.put(key, value);
		return this;
	}

	public static Result build(int i, String message) {
		return new Result(i, message);
	}

}

CustBusinessException.java 类

package com.seesun2012.common.exception;

/**
 * 自定义异常类
 *
 * @author seesun2012@163.com
 *
 */
public class CustBusinessException extends RuntimeException{

	private static final long serialVersionUID = 1L;

	public CustBusinessException(){

	}

	public CustBusinessException(String str){
		super(str);
	}

	public CustBusinessException(Throwable throwable){
		super(throwable);
	}

	public CustBusinessException(String str, Throwable throwable){
		super(str, throwable);
	}

}

TestUtils.java 类

package com.seesun2012.test.utils;

import com.seesun2012.common.entity.Result;
import com.seesun2012.common.entity.Userregister;
import com.seesun2012.common.utils.CommonUtils;

public class TestUtils{

	public static void main(String[] args) {
		Userregister sss = new Userregister();
		sss.setUserAccount("asdflkjasokdfj");
		System.out.println(insertUser(sss));
	}

	public static Result insertUser(Userregister param){
		Result result = new Result(1, "新增失败");
		try {
			CommonUtils.doValidator(param);
			result = Result.build(0, "新增成功");
        } catch (Exception e) {
        	result =  Result.build(1, e.getMessage());
        }
		return result;
	}

}

结语：该用户暂未添加