浅谈java反射和自定义注解的综合应用实例

2019-11-26 11:31:46

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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