java - 使用 GSON 将两个 ArrayList 转换为 JSON

Question

我有一个类 Graph，其中有两个 ArrayList 作为成员变量，我想使用 GSON 库将其转换为 JSON 文件。

这是 Graph 类的代码:

public class Graph {

    private List<Node> nodes;
    private List<Link> links;

    // Constructors, Getters and Setters


}

这是 Node 类的代码:

public class Node {

    private String name;
    private int group;

    // Constructors, Getters and Setters


}

这是类链接的代码:

public class Link {

    private int source;
    private int target;

    // Constructors, Getters and Setters


}

这是我想要生成的 JSON 文件:

{
  "nodes":[
    {"name":"Myriel","group":1},
    {"name":"Napoleon","group":1},
    {"name":"Mlle.Baptistine","group":2},
    {"name":"Mme.Hucheloup","group":2}
  ],
  "links":[
    {"source":1,"target":0},
    {"source":2,"target":0},
    {"source":3,"target":1},
    {"source":3,"target":2}
  ]
}

这是主类:

public class Main {

    public static void main(String[] args) throws IOException {

        Graph graph = new Graph();

        List<Node> nodes = new ArrayList<Node>();
        nodes = DAO.listNodes();    //This function fills the list from a database

        List<Link> links = new ArrayList<Link>();
        links = DAO.listLinks();    //This function fills the list from a database

        graph.setNodes(nodes);
        graph.setLinks(links);

        Writer writer = new FileWriter("output.json");

        Gson gson = new GsonBuilder().setPrettyPrinting().create();
        gson.toJson(graph, writer);

        writer.close();

    }

}

这是我得到的错误:

Exception in thread "main" java.lang.UnsupportedOperationException: Attempted to serialize java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to register a type adapter?
    at com.google.gson.internal.bind.TypeAdapters$1.write(TypeAdapters.java:68)
    at com.google.gson.internal.bind.TypeAdapters$1.write(TypeAdapters.java:61)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ArrayTypeAdapter.write(ArrayTypeAdapter.java:93)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:91)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:206)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:91)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:206)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:91)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:206)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:60)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:91)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:206)
    at com.google.gson.Gson.toJson(Gson.java:595)
    at com.google.gson.Gson.toJson(Gson.java:574)
    at com.google.gson.Gson.toJson(Gson.java:549)
    at gson.Main.main(Main.java:36)

有什么问题吗？我该如何解决它？

Answer 1

我找到了解决方案:

GsonBuilder gsonBuilder = new GsonBuilder();
        gsonBuilder.registerTypeAdapter(Node.class, new NodeAdapter()).registerTypeAdapter(Link.class, new LinkAdapter());
        Gson gson = gsonBuilder.create();
        writer.write(gson.toJson(graph)); 

它确实按照我想要的方式生成了一个 JSON 文件。

感谢您的帮助!

这是 LinkAdapter 类:

public class LinkAdapter implements JsonSerializer<Link> {

    public JsonElement serialize(Link link, Type type,
            JsonSerializationContext jsc) {

        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("source", link.getNodeBySource().getIdNode());
        jsonObject.addProperty("target", link.getNodeByTarget().getIdNode());

        return jsonObject;
    }

}

这是 NodeAdapter 类:

public class NodeAdapter implements JsonSerializer<Node> {

    public JsonElement serialize(Node node, Type type,
            JsonSerializationContext jsc) {

        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("name", node.getName());
        jsonObject.addProperty("group", node.getHyperEdge().getIdHe());

        return jsonObject;
    }


}