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Guava类库中Lists.transform踩坑

前言

最近在Java踩坑的道路上越踩越多坑,随手写篇笔记做个记录。

问题分析

Guava类库很强大,但也有一点坑,最近在做项目的正好遇到。使用Lists.transform转换数据,遇到坑①修改源对象数据会直接影响转换后数据 ②直接修改转换后数据修改无效

代码例子:

import com.google.common.base.Function;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;

import java.util.List;

//源对象
class People {

    private String name;

    private int age;

    private String desc;

    public People() {
    }

    public People(String name, int age, String desc) {
        this.name = name;
        this.age = age;
        this.desc = desc;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    @Override
    public String toString() {
        return "People{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", desc='" + desc + '\'' +
                '}';
    }
}

// 转换目标对象
class PeopleVo {
    private String name;

    private int age;

    private String desc;

    public PeopleVo() {
    }

    public PeopleVo(String name, int age, String desc) {
        this.name = name;
        this.age = age;
        this.desc = desc;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    @Override
    public String toString() {
        return "People{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", desc='" + desc + '\'' +
                '}';
    }
}

public class GuavaExample {

    public static PeopleVo peopleToVo(People people) {
        PeopleVo peopleVo = new PeopleVo();
        peopleVo.setName(people.getName());
        peopleVo.setAge(people.getAge());
        peopleVo.setDesc(people.getDesc() + " To Vo");
        return peopleVo;
    }

    public static void main(String[] args) {
        List<People> peopleList = ImmutableList.of(
                new People("icharle", 18, "good"),
                new People("pad", 19, "better"),
                new People("soarteam", 20, "best")
        );

        List<PeopleVo> peopleVos = Lists.transform(peopleList, new Function<People, PeopleVo>() {
            @Override
            public PeopleVo apply(People people) {
                return peopleToVo(people);
            }
        });

        //1.对源对象数据进行修改会影响到转换对象的数据
        System.out.println("-----------------源对象数据-----------------");
        System.out.println(peopleVos.toString());

        System.out.println("----------------对源对象修改-----------------");
        for(People people : peopleList){
            people.setAge(people.getAge()+1);
        }
        System.out.println(peopleVos.toString());


        //2.对转换后的对象进行修改数据,修改无效
        System.out.println("-----------------修改转换对象数据-----------------");
        for(PeopleVo peopleVo : peopleVos){
            peopleVo.setAge(peopleVo.getAge()+1);
        }
        System.out.println(peopleVos.toString());
    }

}

输出数据:

# 输出片段一
-----------------源对象数据-----------------
[People{name='icharle', age=18, desc='good To Vo'}, People{name='pad', age=19, desc='better To Vo'}, People{name='soarteam', age=20, desc='best To Vo'}]
# 输出片段二
----------------对源对象修改-----------------
[People{name='icharle', age=19, desc='good To Vo'}, People{name='pad', age=20, desc='better To Vo'}, People{name='soarteam', age=21, desc='best To Vo'}]
# 输出片段三
-----------------修改转换对象数据-----------------
[People{name='icharle', age=19, desc='good To Vo'}, People{name='pad', age=20, desc='better To Vo'}, People{name='soarteam', age=21, desc='best To Vo'}]

情况说明:

  • 输出判断一跟片段二对比,当对源数据peopleList的age加一操作情况下,输出转换对象后的数据是更变的。
  • 输出片段二跟片段三对比,当对转换后数据peopleVos的age加一的操作情况下,输出转换对象的数据是不改变。

查阅谷歌相关文章,发现转换后的数据是一个视图模型,因此再修改原对象情况下,必然会影响视图内容;而直接修改视图,对它的任何更改都是无效的。

参考文章:关于Guava类库中Lists.transform的问题解析

标签: Java
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