Java自定义注解实现过程

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());
}
}
}

@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());
}
}
}