Question

我有一个非常大的Java对象，它在内存中表示带有顶点和边的图形。每个顶点都有一个ArrayList个与其连接的顶点（并且具有HashMap数据结构以及其他用途）。该图可以有几千个顶点，还有更多边。

尝试使用Java的内置序列化（implements Serializable等）来序列化图表时，我总是遇到StackOverflowError。将图表的其他属性设置为transient也无济于事，也不会将堆栈大小设置得更大（即-Xss1g或-Xss512m）。

我不认为我需要制作自定义writeObject方法，因为ArrayList和HashMap已经有了自己的实现，这些实现在序列化时调用。

我的问题是：有没有办法在没有StackOverflowError的情况下序列化已经在内存中的大型Java对象？

编辑：这是堆栈跟踪：

Exception in thread "main" java.lang.StackOverflowError
at java.lang.reflect.Method.invoke(Method.java:575)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:950)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1482)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1535)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1413)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1159)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:329)
at java.util.ArrayList.writeObject(ArrayList.java:570)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
// Many more lines after this

以下是我的Graph课程的概述：

public class Graph implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = -2632163054149021990L;
private ArrayList<Vertex> vertices;

private HashMap<Integer, Set<Vertex>> map;

public Graph(int rowMax, int colMax)
{
    map = new HashMap<Integer, Set<Vertex>>();

    this.vertices = new ArrayList<Vertex>();
}

public void connectVertices(Vertex u, Vertex v)
{
    u.addNeighbor(v);
    v.addNeighbor(u);
}

// other unrelated methods after this

这是我的Vertex课程：

public class Vertex implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 8520500010710631610L;
public int row;
public int col;
private ArrayList<Vertex> neighbors; // may change this to Set<Vertex>

public Vertex(int i, int j)
{
    this.row = i;
    this.col = j;
    this.neighbors = new ArrayList<Vertex>();
}

public boolean addNeighbor(Vertex v)
{
    this.neighbors.add(v);
    return true;
}

// unrelated methods after this

编辑2 ：此外，对于尺寸较小但有＃34;邻居＆＃34;的图表，请不要出现此问题。

Answer 1

如果图表的深度太大而无法处理默认序列化，则序列化将抛出StackOverflowError。这是由于默认序列化在解析图形时以递归方式序列化每个节点。

平面结构可以正常工作（例如，具有2000个子节点的父节点），但深层结构将失败（例如，具有2000个后代级别的节点）。

E.g。堆栈溢出：

public class Node implements Serializable
{
    private ArrayList<Node> nodes = new ArrayList<Node>();

    public static void main(String[] args) throws Exception
    {
        Node node = new Node();
        int depth = 3000;

        // Add nodes chained down to specified depth
        Node last = node;
        for (int i = 0; i < depth; i++)
        {
            Node temp = new Node();
            last.nodes.add(temp);
            last = temp;
        }

        System.out.println("starting");

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream out = new ObjectOutputStream(bos);
        // Below line will cause a stack overflow.
        out.writeObject(node);

        System.out.println("done");
    }
}

您需要减少图形的深度以限制递归序列化调用的数量，或者编写自定义序列化来解决此问题。自定义序列化本质上需要是非递归的，不幸的是，乍一看似乎并非易事。

Answer 2

我有类似的问题。经过多次打猎，我发现了一个Kryo叉子，用于处理深层嵌套的物体。通过https://github.com/EsotericSoftware/kryo/issues/103，克隆和mvn clean install https://github.com/romix/kryo/tree/kryo-2.23-continuations。它目前是com.esotericsoftware.kryo:kryo:2.23-SNAPSHOT。

（旁注：关于SO的问题有很多可以用这个来回答。我应该发布答案的副本（如https://stackoverflow.com/a/43327778/513038），或者评论这个答案的链接，或者标记问题作为重复指向这个，或什么？）

Answer 3

我知道这已经晚了，但是当我尝试自己解决此问题时，我是通过Google遇到的。

我想要一个比编写自定义序列化代码所需的代码量少得多的解决方案。

问题是节点已连接到节点。任何给定节点都可以访问网络的很大一部分-对于无向图，它是每个节点。

当您尝试序列化节点时，每个可到达的节点都将最终出现在堆栈中。

最简单的解决方案不是将节点直接连接到其邻居，而是添加一个间接层：

class Node{

    private final Map<NodeRef, Connection> forwardConnections = new HashMap<>();
    private final Map<NodeRef, Connection> reverseConnections = new HashMap<>();

    ...
}

class Connection{

    private final NodeRef source;
    private final NodeRef dest;
    private final ConnectionMetadata meta;

    public Connection(Node source, Node dest, ConnectionMetadata meta){
        this.source = new NodeRef(source);
        this.dest = new NodeRef(dest);
    }

    public Node getSource(){
        return source.resolve();
    }

    public Node getDest(){
        return dest.resolve();
    }

    public ConnectionMetadata getMeta(){
        return meta;
    }

}

public class NodeRef{

    private transient Node node;
    private final Network network;
    private final int[] uid;

    public NodeRef(Node node){
        this.node = node;
        this.network = node.getNetwork();
        this.uid = node.getUID();
    }

    //Won't be called during deserialisation
    public Node resolve(){
        if(node == null){
            node = network.resolve(uid);
        }
        return node;
    }

    //Will be called when connections maps are deserialised.
    public boolean equals(Object o){
        //you might also want to check that the networks are equal
        return (o instanceof NodeRef) && Arrays.equals(uid, ((NodeRef)o).uid);
    }


    //Will be called when connections maps are deserialised.
    public int hashCode(){
        return Arrays.hashCode(uid);
    }
}

在没有StackOverflowError的情况下序列化Java对象

3 个答案: