我们在写项目的时候，如何类比较少。判别指定对象的属性值是否为空，那确实可以，但是随着类的增多，判别对象的属性是否为空就非常的繁琐，所以可以使用自定义注解和反射来判定指定的字段是否为空。
第一步:创建一个自定义注解
package com.zczy.test.annoation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface ParamsCheck {
/**
* 此注解就是过滤不需要的字段，来判断需要的字段是否为空
*/
String attributeName();
}
第二步:创建一个类，并在类的属性上加上自定义注解的标识，就是为了判断这些字段是否为空
package com.zczy.test.bean;
import com.zczy.test.annoation.ParamsCheck;
import lombok.Data;
@Data
public class Person {
@ParamsCheck(attributeName = "userName")
private String userName;
@ParamsCheck(attributeName = "id")
private String id;
private String sex;
public Person(String userName,String id,String sex){
this.userName = userName;
this.id = id;
this.sex = sex;
}
}
第三部:自定义一个返回类型的类
package com.zczy.test.utils;
import lombok.Data;
@Data
public class ValidResult {
private String msg;
private String code;
public ValidResult(){
}
public ValidResult(String msg,String code){
this.msg = msg;
this.code = code;
}
}
第四步:编写反射的代码
package com.zczy.test.utils;
import com.zczy.test.annoation.ParamsCheck;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
public class CheckPointParamsHandlar {
public Class clazz;
private Field[] fields;
private T t;
public CheckPointParamsHandlar(T t){
this.t = t;
this.clazz = t.getClass();
//getDeclaredFields()返回Class中所有的字段，包括私有字段；
//getFields 只返回公共字段，即有public修饰的字段
this.fields = t.getClass().getDeclaredFields();
}
//判断已经注解的字段是否为空
public ValidResult getParamChecksResults(){
List list = new ArrayList<>();
ValidResult res = new ValidResult();
Boolean flag = true;
StringBuffer sb = new StringBuffer();
for(Field field : fields ){
//System.out.println(field);
//private java.lang.String com.zczy.test.bean.Person.userName
//private java.lang.String com.zczy.test.bean.Person.id
//private java.lang.String com.zczy.test.bean.Person.sex
//查看注解的必要字段不能为空--如果没有注解直接跳过
Annotation annotation=null;
annotation = field.getAnnotation(ParamsCheck.class);
if(annotation == null){
continue;
}
//判断注解过的字段是否为空
// System.out.println("annotation>>>>>"+annotation);
//annotation>>>>>@com.zczy.test.annoation.ParamsCheck(attributeName=userName)
//annotation>>>>>@com.zczy.test.annoation.ParamsCheck(attributeName=id)
String name = field.getName();
// System.out.println(name);
// userName
// id
// sex
char[] tempChar = name.toCharArray();
tempChar[0] -= 32;
String tempStr ="get"+ String.valueOf(tempChar);
list.add(tempStr);
//System.out.println("list>>>>>"+list);
// list>>>>>[getUserName, getId]
}
for(String str : list){
try {
Method method = clazz.getMethod(str);
//System.out.println("method>>>"+method);
// method>>>public java.lang.String com.zczy.test.bean.Person.getUserName()
//method>>>public java.lang.String com.zczy.test.bean.Person.getId()
Object invoke = method.invoke(t);
// System.out.println(invoke);
if(null == invoke || "".equals(invoke)){
flag = false;
sb.append(str.toLowerCase()+"不能为空").append(",");
}
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
if(flag == false){
res = new ValidResult(sb.toString(),"1");
}else{
res = new ValidResult("校验成功!","0");
}
return res;
}
}
测试类:
package com.zczy.test.Test;
import com.zczy.test.bean.Person;
import com.zczy.test.utils.CheckPointParamsHandlar;
import com.zczy.test.utils.ValidResult;
public class ParamsCheckTest {
public static void main(String[] args) {
Person person = new Person("1111","22","111");
ValidResult paramChecksResults = new CheckPointParamsHandlar<>(person).getParamChecksResults();
System.out.println(paramChecksResults.toString());
}
}
结果：
测试1：
测试2:
测试3:
测试4:
本文地址：https://blog.csdn.net/trainhui/article/details/107336671
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