浅拷贝是指在对一个对象进行拷贝时，只拷贝对象本身和其中的基本数据类型，而不拷贝对象内部的引用类型。因此，在浅拷贝的对象中，引用类型的变量指向的依旧是原始对象中的引用。

深拷贝是指在对一个对象进行拷贝时，不仅拷贝对象本身和其中的基本数据类型，同时也拷贝对象内部的引用类型。因此，在深拷贝的对象中，引用类型的变量指向的是全新的对象。

cloning

克隆库是一个小型的开源（Apache许可）Java库，用于深度克隆对象。对象不必实现可克隆接口。实际上，这个库可以克隆任何Java对象。如果您不想修改缓存对象，或者每当您想创建对象的深度副本时，它可以在缓存实现中使用。

重要提示：Java类的深度克隆可能意味着数千个对象被克隆！另外，克隆文件和流可能会导致JVM崩溃。强烈建议在开发期间启用将克隆类转储到stdout，以便查看克隆的内容。

  <dependency>
      <groupId>io.github.kostaskougios</groupId>
      <artifactId>cloning</artifactId>
      <version>1.10.3</version>
  </dependency>

Github: https://github.com/kostaskougios/cloning

cloning 测试代码

cloning 可以深度克隆任何 java 对象, 简单对象，复杂对象和集合对象,集合中的每个元素也都会被深度克隆。简单易用，功能强大。

publicclass CloningExp {

    public static void main(String[] args) {
        Cloner cloner = new Cloner();

        // clone 简单对象
        Bean1 bean1 = new Bean1();
        bean1.setF1("XA");
        bean1.setF2(478354);
        System.out.println("bean1 -> " + bean1);

        Bean1 clonedBean1 = cloner.deepClone(bean1);
        System.out.println("clonedBean1 -> " + clonedBean1);
        System.out.println("bean1 == clonedBean1 -> " + (bean1 == clonedBean1));

        // clone 复杂对象
        Bean2 bean2 = new Bean2();
        bean2.setF1("VVV");
        bean2.setF2(bean1);
        System.out.println("bean2 -> " + bean2);

        Bean2 clonedBean2 = cloner.deepClone(bean2);
        System.out.println("clonedBean2 -> " + clonedBean2);
        System.out.println("bean2 == clonedBean2 -> " + (bean2 == clonedBean2));
        System.out.println("bean2.bean1 == clonedBean2.bean1 -> " + (bean2.getF2() == clonedBean2.getF2()));

        // clone 集合
        List<Bean1> bean1List = new ArrayList<>();
        bean1List.add(new Bean1("Bean1-1" , 1));
        bean1List.add(new Bean1("Bean1-2" , 1));
        bean1List.add(new Bean1("Bean1-3" , 1));
        System.out.println("bean1List -> " + bean1List);

        List<Bean1> clonedBean1List = cloner.deepClone(bean1List);
        System.out.println("clonedBean1List -> " + clonedBean1List);
        System.out.println("bean1List == clonedBean1List -> " + (bean1List == clonedBean1List));

        Map<Bean1 , Bean2> map = new HashMap<>();
        Bean1 mapBean1 = new Bean1("Bean1-1", 1);
        Bean2 mapBean2 = new Bean2("Bean2-1", mapBean1);
        map.put(mapBean1 , mapBean2);
        System.out.println("map -> " + map);

        Map<Bean1, Bean2> clonedMap = cloner.deepClone(map);
        System.out.println("clonedMap -> " + clonedMap);
        System.out.println("map == clonedMap -> " + (map == clonedMap));

        Cloner clonedCloner = cloner.deepClone(cloner);
        System.out.println("cloner == clonedCloner -> " + (cloner == clonedCloner));

        Map<String , Object> sourceMap = new HashMap<>();
        sourceMap.put("1" , new Bean1("CAC" , 555));
        sourceMap.put("2" , new Bean1("AXC" , 5589));
        sourceMap.put("3" , new Bean1("bbv" , 76));
        sourceMap.put("4" , "dasfsdgsdg");
        sourceMap.put("5" , new Object());
        sourceMap.put("6" , new ArrayList<>());
        sourceMap.put("7" , 99999999999L);
        sourceMap.put("8" , new HashMap<>());

        long startTimeMillis = System.currentTimeMillis();
        for (int i = 0 ;i < 500000; i++) {
            cloner.deepClone(sourceMap);
        }
        System.out.println("time cost -> " + (System.currentTimeMillis() - startTimeMillis) + " ms");

    }

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    staticclass Bean1 {

        private String f1;

        private Integer f2;

    }

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    staticclass Bean2 {

        private String f1;

        private Bean1 f2;
    }
}

bean1 -> CloningExp.Bean1(f1=XA, f2=478354)
clonedBean1 -> CloningExp.Bean1(f1=XA, f2=478354)
bean1 == clonedBean1 -> false
bean2 -> CloningExp.Bean2(f1=VVV, f2=CloningExp.Bean1(f1=XA, f2=478354))
clonedBean2 -> CloningExp.Bean2(f1=VVV, f2=CloningExp.Bean1(f1=XA, f2=478354))
bean2 == clonedBean2 -> false
bean2.bean1 == clonedBean2.bean1 -> false
bean1List -> [CloningExp.Bean1(f1=Bean1-1, f2=1), CloningExp.Bean1(f1=Bean1-2, f2=1), CloningExp.Bean1(f1=Bean1-3, f2=1)]
clonedBean1List -> [CloningExp.Bean1(f1=Bean1-1, f2=1), CloningExp.Bean1(f1=Bean1-2, f2=1), CloningExp.Bean1(f1=Bean1-3, f2=1)]
bean1List == clonedBean1List -> false
map -> {CloningExp.Bean1(f1=Bean1-1, f2=1)=CloningExp.Bean2(f1=Bean2-1, f2=CloningExp.Bean1(f1=Bean1-1, f2=1))}
clonedMap -> {CloningExp.Bean1(f1=Bean1-1, f2=1)=CloningExp.Bean2(f1=Bean2-1, f2=CloningExp.Bean1(f1=Bean1-1, f2=1))}
map == clonedMap -> false
cloner == clonedCloner -> false
time cost -> 447 ms

cloning 性能

Map<String , Object> sourceMap = new HashMap<>();
sourceMap.put("1" , new Bean1("CAC" , 555));
sourceMap.put("2" , new Bean1("AXC" , 5589));
sourceMap.put("3" , new Bean1("bbv" , 76));
sourceMap.put("4" , "dasfsdgsdg");
sourceMap.put("5" , new Object());
sourceMap.put("6" , new ArrayList<>());
sourceMap.put("7" , 99999999999L);
sourceMap.put("8" , new HashMap<>());

对 sourceMap 克隆 50万次耗时 447 ms

Apache Commons Lang3

Apache Commons Lang3 中有一个 SerializationUtils 类用来对目标对象进行深度克隆，它内部使用的是 JDK 内置的对对象的序列化和反序列化，所以使用 SerializationUtils 有个前提是对象必须实现了 Serializable 接口。

 <dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.13.0</version>
</dependency>

SerializationUtils 测试代码

publicclass SerializationUtilsExp {

    public static void main(String[] args) {

        // clone 简单对象
        Bean1 bean1 = new Bean1();
        bean1.setF1("XA");
        bean1.setF2(478354);
        System.out.println("bean1 -> " + bean1);

        Bean1 clonedBean1 = SerializationUtils.clone(bean1);
        System.out.println("clonedBean1 -> " + clonedBean1);
        System.out.println("bean1 == clonedBean1 -> " + (bean1 == clonedBean1));

        // clone 复杂对象
        Bean2 bean2 = new Bean2();
        bean2.setF1("VVV");
        bean2.setF2(bean1);
        System.out.println("bean2 -> " + bean2);

        Bean2 clonedBean2 = SerializationUtils.clone(bean2);
        System.out.println("clonedBean2 -> " + clonedBean2);
        System.out.println("bean2 == clonedBean2 -> " + (bean2 == clonedBean2));
        System.out.println("bean2.bean1 == clonedBean2.bean1 -> " + (bean2.getF2() == clonedBean2.getF2()));

        // clone 集合
        ArrayList<Bean1> bean1List = new ArrayList<>();
        bean1List.add(new Bean1("Bean1-1" , 1));
        bean1List.add(new Bean1("Bean1-2" , 1));
        bean1List.add(new Bean1("Bean1-3" , 1));
        System.out.println("bean1List -> " + bean1List);

        List<Bean1> clonedBean1List = SerializationUtils.clone(bean1List);
        System.out.println("clonedBean1List -> " + clonedBean1List);
        System.out.println("bean1List == clonedBean1List -> " + (bean1List == clonedBean1List));

        HashMap<Bean1, Bean2> map = new HashMap<>();
        Bean1 mapBean1 = new Bean1("Bean1-1", 1);
        Bean2 mapBean2 = new Bean2("Bean2-1", mapBean1);
        map.put(mapBean1 , mapBean2);
        System.out.println("map -> " + map);

        Map<Bean1, Bean2> clonedMap = SerializationUtils.clone(map);
        System.out.println("clonedMap -> " + clonedMap);
        System.out.println("map == clonedMap -> " + (map == clonedMap));

        HashMap<String , Object> sourceMap = new HashMap<>();
        sourceMap.put("1" , new Bean1("CAC" , 555));
        sourceMap.put("2" , new Bean1("AXC" , 5589));
        sourceMap.put("3" , new Bean1("bbv" , 76));
        sourceMap.put("4" , "dasfsdgsdg");
        sourceMap.put("5" , "AAAAAAAAAAAAAA");
        sourceMap.put("6" , new ArrayList<>());
        sourceMap.put("7" , 99999999999L);
        sourceMap.put("8" , new HashMap<>());

        long startTimeMillis = System.currentTimeMillis();
        for (int i = 0 ;i < 500000; i++) {
            SerializationUtils.clone(sourceMap);
        }
        System.out.println("time cost -> " + (System.currentTimeMillis() - startTimeMillis) + " ms");
    }

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    staticclass Bean1 implements Serializable {

        private String f1;

        private Integer f2;

    }

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    staticclass Bean2 implements Serializable {

        private String f1;

        private Bean1 f2;
    }
}

bean1 -> SerializationUtilsExp.Bean1(f1=XA, f2=478354)
clonedBean1 -> SerializationUtilsExp.Bean1(f1=XA, f2=478354)
bean1 == clonedBean1 -> false
bean2 -> SerializationUtilsExp.Bean2(f1=VVV, f2=SerializationUtilsExp.Bean1(f1=XA, f2=478354))
clonedBean2 -> SerializationUtilsExp.Bean2(f1=VVV, f2=SerializationUtilsExp.Bean1(f1=XA, f2=478354))
bean2 == clonedBean2 -> false
bean2.bean1 == clonedBean2.bean1 -> false
bean1List -> [SerializationUtilsExp.Bean1(f1=Bean1-1, f2=1), SerializationUtilsExp.Bean1(f1=Bean1-2, f2=1), SerializationUtilsExp.Bean1(f1=Bean1-3, f2=1)]
clonedBean1List -> [SerializationUtilsExp.Bean1(f1=Bean1-1, f2=1), SerializationUtilsExp.Bean1(f1=Bean1-2, f2=1), SerializationUtilsExp.Bean1(f1=Bean1-3, f2=1)]
bean1List == clonedBean1List -> false
map -> {SerializationUtilsExp.Bean1(f1=Bean1-1, f2=1)=SerializationUtilsExp.Bean2(f1=Bean2-1, f2=SerializationUtilsExp.Bean1(f1=Bean1-1, f2=1))}
clonedMap -> {SerializationUtilsExp.Bean1(f1=Bean1-1, f2=1)=SerializationUtilsExp.Bean2(f1=Bean2-1, f2=SerializationUtilsExp.Bean1(f1=Bean1-1, f2=1))}
map == clonedMap -> false
time cost -> 26061 ms

SerializationUtils 性能

HashMap<String , Object> sourceMap = new HashMap<>();
sourceMap.put("1" , new Bean1("CAC" , 555));
sourceMap.put("2" , new Bean1("AXC" , 5589));
sourceMap.put("3" , new Bean1("bbv" , 76));
sourceMap.put("4" , "dasfsdgsdg");
sourceMap.put("5" , "AAAAAAAAAAAAAA");
sourceMap.put("6" , new ArrayList<>());
sourceMap.put("7" , 99999999999L);
sourceMap.put("8" , new HashMap<>());

对 sourceMap 克隆 50万次耗时 25716 ms

其他一些深拷贝的方式

1. new 对象 (太累了且不优雅)
2. JSON 序列化
3. 使用一些对象序列化库,例如：Protocol Buffers , Kryo , ProtoStuff , Hessian ;