java - Spring BeanUtils 使用 List 字段复制属性

Question

我有如下所示的 Foo 和 Item 类。

import java.util.ArrayList;
import java.util.List;

public class Foo {
    private Long id;
    private List<Item> items;

    public Foo(Long id) {
        this.id = id;
        this.items = new ArrayList<Item>();
    }

    public Long getId() {
        return id;
    }

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

    public List<Item> getItems() {
        return items;
    }

    public void setItems(List<Item> items) {
        this.items = items;
    }
}


public class Item {
    private String bar;

    public Item(String bar) {
        this.bar = bar;
    }

    public String getBar() {
        return bar;
    }

    public void setBar(String bar) {
        this.bar = bar;
    }

    @Override
    public String toString() {
        return "Item{" + "bar='" + bar + '\'' + '}';
    }
}

当我使用 spring BeanUtils 复制 Foo 类时，列表字段的引用没有改变。

import org.springframework.beans.BeanUtils;

public class SimpleCopyMain {

    public static void main(String[] args) {
        Foo foo = new Foo(1L);
        foo.getItems().add(new Item("item1"));
        foo.getItems().add(new Item("item2"));

        Foo fooSnapShot = new Foo(100L);
        BeanUtils.copyProperties(foo,fooSnapShot);

        foo.setId(999L);
        System.out.println("fooSnapShot id field value is not changing as expected : " + fooSnapShot.getId());

        foo.getItems().add(new Item("item3"));

        System.out.println("fooSnapShot items value is changing unexpectedly : " + fooSnapShot.getItems());
    }
}

SimpleCopyMain 类的输出如下:

fooSnapShot id field value is not changing as expected : 1
fooSnapShot items value is changing unexpectedly : [Item{bar='item1'}, Item{bar='item2'}, Item{bar='item3'}]

但是，当我为列表字段创建一个新实例并逐个复制引用时，我得到了预期的行为。

import java.util.ArrayList;

import org.springframework.beans.BeanUtils;

public class CopyMain {

    public static void main(String[] args) {
        Foo foo = new Foo(1L);
        foo.getItems().add(new Item("item1"));
        foo.getItems().add(new Item("item2"));

        Foo fooSnapShot = new Foo(100L);
        BeanUtils.copyProperties(foo, fooSnapShot);

        fooSnapShot.setItems(new ArrayList<Item>(foo.getItems().size()));
        for(int i = 0; i < foo.getItems().size(); i++){
            Item anItem = new Item("");
            BeanUtils.copyProperties(foo.getItems().get(i), anItem);
            fooSnapShot.getItems().add(anItem);
        }

        foo.setId(999L);
        System.out.println("fooSnapShot id field value is not changing as expected : " + fooSnapShot.getId());

        foo.getItems().add(new Item("item3"));

        System.out.println("fooSnapShot items value is is not changing : " + fooSnapShot.getItems());
    }
}

这是输出:

fooSnapShot id field value is not changing as expected : 1
fooSnapShot items value is is not changing : [Item{bar='item1'}, Item{bar='item2'}]

还有我的 pom:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.question</groupId>
    <artifactId>beanutils</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>4.3.3.RELEASE</version>
        </dependency>
    </dependencies>
</project>

为什么 spring beanutils 不克隆列表字段？

Answer 1

根据 BeanUtil copyProperities 方法的实现，Spring 正在通过 Getters 和 Setters 复制您的数据。如果您有像 Integer 这样的基元，那没问题，但是对于您的 List 字段，您正在 Setter 中传递引用。

如果你想让它工作，你需要将你的 setter 更改为:

public void setItems(List<Item> items) {
        this.items = new ArrayList<>(items);
}

这也会进行浅拷贝，但您不会有列表引用。