java反射和自定义注解的综合应用

前言

前几天学习了反射和自定义注解，刚好工作中遇到一个小问题：前台传递到后台的必填字段为空，导致不能插入数据库。就是这样一个小问题，让我考虑到是否可以做一个通用的方法，让前台传递过来的必填字段在后台也校验一遍，如果传递为空，则把响应字段返回提示。因此，我考虑的是用注解的方式，在必填字段上面定义，利用反射得到必填字段的字段名，判断是否为空，并返回响应的信息。

需求模拟

假设客户有：姓名，年龄，地址，手机号码，身份证号等信息，而我们是做金融业务，所以关键是看客户的三要素：姓名，身份证号，手机号码。我们要保证前台传递过来的这三个值不为空。

废话不多说，直接上代码。只看红框里面的即可。

目录结构

客户信息类：Customer

这个是个实体类，我们在：姓名，身份证号码，手机号码上都用了我们的自定义注解。

package com.dao.chu.po;

/**
*
* <p>Title: Customer</p>
* <p>Description:客户信息实体 </p>
*/
public class Customer {

private int id;
@IsRequired
private String name; // 姓名
@IsRequired
private String idnum; // 身份证号码
@IsRequired
private String phone; // 手机号
private String sex; // 性别
private int age; // 年龄
private String address; // 地址

@Override
public String toString() {
return "Customer [id=" + id + ", name=" + name + ", idnum=" + idnum
+ ", phone=" + phone + ", sex=" + sex + ", age=" + age
+ ", address=" + address + "]";
}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

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

public String getIdnum() {
return idnum;
}

public void setIdnum(String idnum) {
this.idnum = idnum;
}

public String getPhone() {
return phone;
}

public void setPhone(String phone) {
this.phone = phone;
}

public String getSex() {
return sex;
}

public void setSex(String sex) {
this.sex = sex;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public String getAddress() {
return address;
}

public void setAddress(String address) {
this.address = address;
}

}

自定义注解类：IsRequired

package com.dao.chu.po;

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

/**
*
* <p>Title: IsRequired</p>
* <p>Description: 字段是否必填 </p>
*/
@Retention(value = RetentionPolicy.RUNTIME)
@Target(value = {ElementType.FIELD})
public @interface IsRequired
{
/**
*

* <p>Title: isRequired</p>
* <p>Description:true:必填  false:非必填 </p>
* @return
*/
boolean isRequired() default true;
}

关键工具类：PoUtils

我们在这个类里面主要用了反射的知识，得到带有自定义注解的字段，并取得这个对象的值进行判断

package com.dao.chu.po;

import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;

import javax.jws.WebResult;

import com.sun.xml.internal.ws.util.StringUtils;

/**
*
* <p>Title: PoUtils</p>
* <p>Description:Po操作工具类  </p>
*/
@SuppressWarnings("unused")
public class PoUtils
{

/**
* <p>Title: getProperties</p>
* <p>Description: 获取javabean属性通用方法 </p>
* @param t
* @param beanName
* @return
* @throws IllegalAccessException
* @throws IllegalArgumentException
* @throws InvocationTargetException
* @throws IntrospectionException
*/
private static <T> Object getProperties(T t, String beanName)
throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, IntrospectionException
{
Object nameValue = new PropertyDescriptor(beanName, t.getClass()).getReadMethod().invoke(t);
return nameValue;
}

/**
* <p>Title: IsFieldBlank</p>
* <p>Description:判断前台传过来的必填字段是否为空 ,不正确则将相应字段返回  </p>
* @param t
* @return
* @throws IllegalAccessException
* @throws IllegalArgumentException
* @throws InvocationTargetException
* @throws IntrospectionException
*/
public static <T> RespBody IsFieldBlank(T t)
throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, IntrospectionException
{
RespBody respBody = new RespBody();
StringBuffer sb = new StringBuffer();

Field[] declaredFields = t.getClass().getDeclaredFields();
for (Field field : declaredFields)
{
field.setAccessible(true);
String name = field.getName();
boolean fieldHasAnno = field.isAnnotationPresent(IsRequired.class);
if (fieldHasAnno)
{
IsRequired annotation = field.getAnnotation(IsRequired.class);
boolean required = annotation.isRequired();
if (required)
{
Object value = getProperties(t, name);
if (null == value)
{
sb.append(name + ",");
}
}
}
}

if (null==sb.toString()||"".equals(sb.toString()))
{
respBody.isSuccess();
}

respBody.setSuccess(false);
respBody.setMsg(sb.toString().substring(0,sb.toString().lastIndexOf(",")) + " is required");
return respBody;
}
}

RespBody：响应实体类

封装了响应的成功失败以及一些信息

package com.dao.chu.po;

/**
*
* <p>Title: RespBody</p>
* <p>Description: 响应实体类</p>
*/
public class RespBody
{
private boolean isSuccess = true;

private String msg;

private Object data;

public boolean isSuccess()
{
return isSuccess;
}

public void setSuccess(boolean isSuccess)
{
this.isSuccess = isSuccess;
}

public String getMsg()
{
return msg;
}

public void setMsg(String msg)
{
this.msg = msg;
}

public Object getData()
{
return data;
}

public void setData(Object data)
{
this.data = data;
}

public RespBody(boolean isSuccess, String msg, Object data)
{
super();
this.isSuccess = isSuccess;
this.msg = msg;
this.data = data;
}

public RespBody(boolean isSuccess, String msg)
{
super();
this.isSuccess = isSuccess;
this.msg = msg;
}

public RespBody()
{
}

@Override
public String toString()
{
return "ReturnBody [isSuccess=" + isSuccess + ", msg=" + msg + ", data=" + data + "]";
}
}

测试类：IsRequiredTest

package com.dao.chu.po;

/**
*
* <p>Title: IsRequiredTest</p>
* <p>Description: 必填成员变量测试类</p>
*/
public class IsRequiredTest {

public static void main(String[] args) {

Customer customer = new Customer();

try {
//=========第一次不赋值==========
RespBody respBody = PoUtils.IsFieldBlank(customer);
//不通过则返回提示信息
if (!respBody.isSuccess()) {
System.out.println("1."+respBody.getMsg());
}

//=========第二次给姓名赋值==========
customer.setName("张三");
respBody = PoUtils.IsFieldBlank(customer);
//不通过则返回提示信息
if (!respBody.isSuccess()) {
System.out.println("2."+respBody.getMsg());
}

} catch (Exception e) {
e.printStackTrace();
}
}

}

输出结果

第一次三个值都为空，提示三个都是必填的，第二次因为姓名赋值了，所以提示另外两个是必填的，本次实验宣告结束，本人知识有限，若有更好的方法欢迎指正