浅谈java反射和自定义注解的综合应用实例

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

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。

原文链接：http://blog.csdn.net/daochuwenziyao/article/details/77755314?utm_source=tuicool&utm_medium=referral