寻求值为复杂对象的Map深拷贝替代方案（原Gson存内存问题）

问题背景 #

• 此前使用Gson实现Map深拷贝，能保证修改拷贝后的Map不会影响原Map，但出现线程持有问题：堆转储中存在大量Gson相关条目，内存持续增长，最终导致请求被拒。
• 尝试过orgMap.clone()、new HashMap<>(orgMap)、copymap.putAll(orgMap)这些浅拷贝方式，均无法对Map的value对象实现深拷贝——修改拷贝Map中的value会同时影响原Map和拷贝后的Map。

堆转储线程调用栈 #

Processing Thread 13running , holding [ at
com.google.gson.stream.JsonReader.doPeek(JsonReader.java:593) at
com.google.gson.stream.JsonReader.peek(JsonReader.java:433) at
com.google.gson.internal.bind.TypeAdapters$7.read(TypeAdapters.java:244) at
com.google.gson.internal.bind.TypeAdapters$7.read(TypeAdapters.java:241) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.readIntoField(ReflectiveTypeAdapterFactory.java:212) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$FieldReflectionAdapter.readField(ReflectiveTypeAdapterFactory.java:433) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:393) at
com.google.gson.Gson$FutureTypeAdapter.read(Gson.java:1367) at
com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40) at
com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82) at
com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.readIntoField(ReflectiveTypeAdapterFactory.java:212) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$FieldReflectionAdapter.readField(ReflectiveTypeAdapterFactory.java:433) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:393) at
com.google.gson.Gson$FutureTypeAdapter.read(Gson.java:1367) at
com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40) at
com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82) at
com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.readIntoField(ReflectiveTypeAdapterFactory.java:212) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$FieldReflectionAdapter.readField(ReflectiveTypeAdapterFactory.java:433) at
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:393) at
com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40) at
com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:186) at
com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:144) at
com.google.gson.Gson.fromJson(Gson.java:1227) at
com.google.gson.Gson.fromJson(Gson.java:1137) at
com.google.gson.Gson.fromJson(Gson.java:1047) at
com.google.gson.Gson.fromJson(Gson.java:1014) at
com.util.getDeepCopyOfMap(Utils.java:2398) at
com.util.ParameterPopulation.applyFiltering(ParameterPopulation.java:800) at
com.util.ParameterPopulation.populateSchemaParameters(ParameterPopulation.java:506) at
com.util.ParameterPopulation.formAvroRequestBasedOnSession(ParameterPopulation.java:440) at
com.util.ParameterPopulation.populateLocationRelatedParameters(ParameterPopulation.java:1343) at
com.util.ParameterPopulation.localProcess(ParameterPopulation.java:294) at
com.util.AbstractProcessingActivity.process(AbstractProcessingActivity.java:30) at
com.util.TransactionImpl.run(TransactionImpl.java:415) at
com.util.TransactionHandlerImpl$FaultTolerantTransaction.run(TransactionHandlerImpl.java:466) at
java.util.concurrent.ThreadPoolExecutor.runWorker(java.base@11.0.20/ThreadPoolExecutor.java:1128) at
java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base@11.0.20/ThreadPoolExecutor.java:628) at
java.lang.Thread.run(java.base@11.0.20/Thread.java:829)

可行替代方案 #

1. 手动实现深拷贝 #

针对Map中Value的具体类型，编写自定义拷贝逻辑，精准控制每个Value的深拷贝：

public static <K, V> Map<K, V> deepCopyMap(Map<K, V> original, Function<V, V> valueCopier) {
    Map<K, V> copiedMap = new HashMap<>();
    for (Map.Entry<K, V> entry : original.entrySet()) {
        copiedMap.put(entry.getKey(), valueCopier.apply(entry.getValue()));
    }
    return copiedMap;
}

示例：若Value为自定义User对象，可传入user -> new User(user.getId(), user.getName(), user.getAddress().clone())作为拷贝函数，确保嵌套对象也被深拷贝。

2. 使用Apache Commons Lang的SerializationUtils #

通过序列化实现通用深拷贝，要求Map的Key和Value均实现Serializable接口：

import org.apache.commons.lang3.SerializationUtils;

public static <K, V> Map<K, V> deepCopyMap(Map<K, V> original) {
    return SerializationUtils.clone(original);
}

注意：该方式性能略低，且不支持不可序列化的类型。

3. 基于Jackson实现深拷贝 #

与Gson逻辑类似，但Jackson的线程安全性更优，内存泄漏风险更低：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.core.type.TypeReference;

private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

public static <K, V> Map<K, V> deepCopyMap(Map<K, V> original) throws IOException {
    String json = OBJECT_MAPPER.writeValueAsString(original);
    return OBJECT_MAPPER.readValue(json, new TypeReference<Map<K, V>>() {});
}

建议使用单例ObjectMapper实例，避免重复创建带来的性能开销。

4. 模型类实现Cloneable接口 #

若Value为自定义模型类，让类实现Cloneable并重写clone()方法，实现自身的深拷贝逻辑：

public class User implements Cloneable {
    private String id;
    private String name;
    private Address address; // 嵌套对象需同样实现Cloneable

    @Override
    protected Object clone() throws CloneNotSupportedException {
        User cloned = (User) super.clone();
        cloned.address = (Address) address.clone(); // 深拷贝嵌套对象
        return cloned;
    }
}

拷贝Map时遍历每个Entry，调用Value的clone()方法放入新Map即可。

内容的提问来源于stack exchange，提问作者Ganesh ram