Java 如何使用 springframework BeanUtils copyProperties 忽略空值？

How to ignore null values using springframework BeanUtils copyProperties?

提问by Fingolricks

I would like to know how to copy the properties from an Object Source to an Object Dest ignoring null values?? using Spring Framework.

我想知道如何将属性从对象源复制到对象目的地而忽略空值？？使用 Spring 框架。

I actually use Apache beanutils, with this code

我实际上使用 Apache beanutils，使用此代码

    beanUtils.setExcludeNulls(true);
    beanUtils.copyProperties(dest, source);

to do it. But now i need to use Spring.

去做吧。但现在我需要使用 Spring。

Any help?

有什么帮助吗？

Thx a lot

多谢

采纳答案by Alfred Xiao

You can create your own method to copy properties while ignoring null values.

您可以创建自己的方法来复制属性，同时忽略空值。

public static String[] getNullPropertyNames (Object source) {
    final BeanWrapper src = new BeanWrapperImpl(source);
    java.beans.PropertyDescriptor[] pds = src.getPropertyDescriptors();

    Set<String> emptyNames = new HashSet<String>();
    for(java.beans.PropertyDescriptor pd : pds) {
        Object srcValue = src.getPropertyValue(pd.getName());
        if (srcValue == null) emptyNames.add(pd.getName());
    }

    String[] result = new String[emptyNames.size()];
    return emptyNames.toArray(result);
}

// then use Spring BeanUtils to copy and ignore null using our function
public static void myCopyProperties(Object src, Object target) {
    BeanUtils.copyProperties(src, target, getNullPropertyNames(src));
}

回答by Pawe? Kaczorowski

Java 8 version of getNullPropertyNames method from alfredx's post:

alfredx帖子中 getNullPropertyNames 方法的 Java 8 版本：

public static String[] getNullPropertyNames(Object source) {
    final BeanWrapper wrappedSource = new BeanWrapperImpl(source);
    return Stream.of(wrappedSource.getPropertyDescriptors())
            .map(FeatureDescriptor::getName)
            .filter(propertyName -> wrappedSource.getPropertyValue(propertyName) == null)
            .toArray(String[]::new);
}

回答by Kumar Abhishek

SpringBeans.xml

SpringBeans.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

    <bean id="source" class="com.core.HelloWorld">
        <property name="name" value="Source" />
        <property name="gender" value="Male" />
    </bean>

    <bean id="target" class="com.core.HelloWorld">
        <property name="name" value="Target" />
    </bean>

</beans>

1. Create a java Bean,

   public class HelloWorld {
       private String name;
       private String gender;
   
       public void printHello() {
           System.out.println("Spring 3 : Hello ! " + name + "    -> gender      -> " + gender);
       }
   
       //Getters and Setters
   }
   

2. Create Main Class to test

   public class App {
       public static void main(String[] args) {
           ApplicationContext context = new ClassPathXmlApplicationContext("SpringBeans.xml");
   
           HelloWorld source = (HelloWorld) context.getBean("source");
           HelloWorld target = (HelloWorld) context.getBean("target");
   
           String[] nullPropertyNames = getNullPropertyNames(target);
           BeanUtils.copyProperties(target,source,nullPropertyNames);
           source.printHello();
       }
   
       public static String[] getNullPropertyNames(Object source) {
           final BeanWrapper wrappedSource = new BeanWrapperImpl(source);
           return Stream.of(wrappedSource.getPropertyDescriptors())
               .map(FeatureDescriptor::getName)
               .filter(propertyName -> wrappedSource.getPropertyValue(propertyName) == null)
               .toArray(String[]::new);
       }
   }
   

2. 创建一个java Bean，

   public class HelloWorld {
       private String name;
       private String gender;
   
       public void printHello() {
           System.out.println("Spring 3 : Hello ! " + name + "    -> gender      -> " + gender);
       }
   
       //Getters and Setters
   }
   

3. 创建主类进行测试

   public class App {
       public static void main(String[] args) {
           ApplicationContext context = new ClassPathXmlApplicationContext("SpringBeans.xml");
   
           HelloWorld source = (HelloWorld) context.getBean("source");
           HelloWorld target = (HelloWorld) context.getBean("target");
   
           String[] nullPropertyNames = getNullPropertyNames(target);
           BeanUtils.copyProperties(target,source,nullPropertyNames);
           source.printHello();
       }
   
       public static String[] getNullPropertyNames(Object source) {
           final BeanWrapper wrappedSource = new BeanWrapperImpl(source);
           return Stream.of(wrappedSource.getPropertyDescriptors())
               .map(FeatureDescriptor::getName)
               .filter(propertyName -> wrappedSource.getPropertyValue(propertyName) == null)
               .toArray(String[]::new);
       }
   }
   

回答by bpedroso

I advise you to use ModelMapper.

我建议你使用 ModelMapper。

This is a sample code that solves your doubt.

这是一个示例代码，可以解决您的疑问。

      ModelMapper modelMapper = new ModelMapper();
modelMapper.getConfiguration().setSkipNullEnabled(true).setMatchingStrategy(MatchingStrategies.STRICT);

      Company a = new Company();
      a.setId(123l);
      Company b = new Company();
      b.setId(456l);
      b.setName("ABC");

      modelMapper.map(a, b);

      System.out.println("->" + b.getName());

It should print the B value. But if you set the "A" name, the result is a print of "A" value.

它应该打印 B 值。但是，如果您设置“A”名称，结果将打印“A”值。

The secret is changing the value of SkipNullEnabled to true.

秘诀是将 SkipNullEnabled 的值更改为 true。

ModelMapper

模型映射器

ModelMapper MVN

模型映射器 MVN

回答by Kamaljit Sidhu

public static List<String> getNullProperties(Object source) {
    final BeanWrapper wrappedSource = new BeanWrapperImpl(source);
    return Stream.of(wrappedSource.getPropertyDescriptors())
        .map(FeatureDescriptor::getName)
        .filter(propertyName -> Objects.isNull(wrappedSource.getPropertyValue(propertyName)))
        .collect(Collectors.toList());

回答by sadhen

A better solution based on Pawel Kaczorowski's answer:

基于 Pawel Kaczorowski 的回答的更好的解决方案：

public static String[] getNullPropertyNames(Object source) {
    final BeanWrapper wrappedSource = new BeanWrapperImpl(source);
    return Stream.of(wrappedSource.getPropertyDescriptors())
        .map(FeatureDescriptor::getName)
        .filter(propertyName -> {
            try {
               return wrappedSource.getPropertyValue(propertyName) == null
            } catch (Exception e) {
               return false
            }                
        })
        .toArray(String[]::new);
}

For example, if we have a DTO:

例如，如果我们有一个 DTO：

class FooDTO {
    private String a;
    public String getA() { ... };
    public String getB();
}

Other answers will throw exceptions on this special case.

其他答案将在这种特殊情况下引发异常。