Java自定义注解实现过程

步骤
1、创建自定义注解类，并添加校验规则
2、解析自定义注解类并实现校验方法
3、创建测试类并声明自定义注解
4、编写Junit测试类测试结果

自定义注解类

package com.swk.common.annotation;

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

/**
 * 自定义注解类
 * @author fuyuwei
 * @Retention: 定义注解的保留策略
 * @Retention(RetentionPolicy.SOURCE)  注解仅存在于源码中，在class字节码文件中不包含
   @Retention(RetentionPolicy.CLASS)   默认的保留策略，注解会在class字节码文件中存在，但运行时无法获得，
   @Retention(RetentionPolicy.RUNTIME) 注解会在class字节码文件中存在，在运行时可以通过反射获取到

   @Target 注释类型声明
   CONSTRUCTOR 构造方法声明
   FIELD 字段声明（包括枚举常量）
   LOCAL_VARIABLE 局部变量声明
   METHOD 方法声明
   PACKAGE 包声明
   PARAMETER 参数声明
   TYPE 类、接口（包括注释类型）或枚举声明
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE,ElementType.FIELD,ElementType.PARAMETER})
public @interface CustomAnnotation {

    /**
     * 是否为空
     * @return
     */
    boolean isNull() default false;

    /**
     * 最大长度
     * @return
     */
    int maxLength() default 8;

    /**
     * 字段描述
     * @return
     */
    String description() default "";

}

实现自定义注解类规则读取与校验

package com.swk.common.annotation;

import java.lang.reflect.Field;
import java.util.concurrent.ConcurrentHashMap;

import org.springframework.util.StringUtils;

import com.swk.common.enums.CommonPostCode;
import com.swk.common.exception.PostingException;


/**
 * 解析自定义注解，并完成校验
 * @author fuyuwei
 */
public class AnnotationChecker {

    private final static ConcurrentHashMap<String,Field[]> fieldsMap = new ConcurrentHashMap<String, Field[]>();

    public AnnotationChecker(){
        super();
    }

    public static void checkParam(Object object) throws PostingException{
        Class<? extends Object> clazz = object.getClass();
        Field[] fields = null;
        if(fieldsMap.containsKey(clazz.getName())){
            fields = fieldsMap.get(clazz.getName());
        }
        // getFields:获得某个类的所有的公共（public）的字段，包括父类;getDeclaredFields获得某个类的所有申明的字段，即包括public、private和proteced，但是不包括父类的申明字段
        else{
            fields = clazz.getDeclaredFields();
            fieldsMap.put(clazz.getName(), fields);
        }
        for(Field field:fields){
            synchronized(field){
                field.setAccessible(true);
                check(field, object);
                field.setAccessible(false);
            }
        }
    }

    private static void check(Field field,Object object) throws PostingException{
        String description;
        Object value = null;
        CustomAnnotation ca = field.getAnnotation(CustomAnnotation.class);
        try {
            value = field.get(object);
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        if (ca == null) return;
        // 如果没有标注description默认展示字段名称
        description = ca.description().equals("")?field.getName():ca.description();
        if(!ca.isNull()){
            if(value == null || StringUtils.isEmpty(value.toString().trim())){
                throw new PostingException(CommonPostCode.PARAM_LENGTH.getErrorCode(),description+" "+CommonPostCode.PARAM_NULL.getErrorMesage());
            }
        }
        if(value.toString().length() > ca.maxLength()){
            throw new PostingException(CommonPostCode.PARAM_LENGTH.getErrorCode(),description+" "+CommonPostCode.PARAM_LENGTH.getErrorCode());
        }
    }
}

创建依赖的其他类

枚举类

package com.swk.common.enums;

public enum CommonPostCode {

    PARAM_NULL(-1,"param required"),
    PARAM_LENGTH(-2,"param too long");

    private int errorCode;

    private String errorMesage;


    private CommonPostCode(int errorCode, String errorMesage) {
        this.errorCode = errorCode;
        this.errorMesage = errorMesage;
    }

    public int getErrorCode() {
        return errorCode;
    }

    public void setErrorCode(int errorCode) {
        this.errorCode = errorCode;
    }

    public String getErrorMesage() {
        return errorMesage;
    }

    public void setErrorMesage(String errorMesage) {
        this.errorMesage = errorMesage;
    }


}

自定义异常类

package com.swk.common.exception;

public class PostingException extends RuntimeException {

    private static final long serialVersionUID = 5969404579580331293L;

    private int errorCode;

    private String errorMessage;

    public PostingException(int errorCode, String errorMessage) {
        super();
        this.errorCode = errorCode;
        this.errorMessage = errorMessage;
    }

    public int getErrorCode() {
        return errorCode;
    }

    public void setErrorCode(int errorCode) {
        this.errorCode = errorCode;
    }

    public String getErrorMessage() {
        return errorMessage;
    }

    public void setErrorMessage(String errorMessage) {
        this.errorMessage = errorMessage;
    }



}

创建声明自定义注解的测试类

package com.swk.request;

import com.swk.common.annotation.CustomAnnotation;

public class UserInfoRequest {

    @CustomAnnotation(isNull=false,maxLength=4,description="姓名")
    private String name;

    @CustomAnnotation(isNull=false,maxLength=11,description="手机号")
    private String mobile;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getMobile() {
        return mobile;
    }

    public void setMobile(String mobile) {
        this.mobile = mobile;
    }


}

编写Junit测试类

package com.swk.test.annotation;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.sun.istack.internal.logging.Logger;
import com.swk.common.annotation.AnnotationChecker;
import com.swk.common.exception.PostingException;
import com.swk.request.UserInfoRequest;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:spring-mybatis.xml"})
public class AnnotationTest {

    private Logger logger = Logger.getLogger(AnnotationTest.class);

    @Test
    public void testAnnotation(){
        UserInfoRequest request = new UserInfoRequest();
        try {
            AnnotationChecker.checkParam(request);
        } catch (PostingException e) {
            logger.info(e.getErrorCode()+":"+e.getErrorMessage());
        }
    }
}

运行结果

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:spring-mybatis.xml"})
public class AnnotationTest {

    private Logger logger = Logger.getLogger(AnnotationTest.class);

    @Test
    public void testAnnotation(){
        UserInfoRequest request = new UserInfoRequest();
        request.setName("齐天大圣孙悟空");
        try {
            AnnotationChecker.checkParam(request);
        } catch (PostingException e) {
            logger.info(e.getErrorCode()+":"+e.getErrorMessage());
        }
    }
}

运行结果