java - Playframework，将 JSON 转换为模型(使用 Gson)，保存模型失败

Question

我正在尝试将 JSON 字符串转换为我的模型类。我在游戏框架内使用吗啡。

以下是相关代码行:

public static void add(JsonObject body) {
    System.out.println(body); // -> {"title":"test2","url":"http://www.gmx.de","description":"eine beschreibung für das lesezeichen","tags":["tag1","tag2","tag3","tag5","tag0209135913598"],"is_private":true}
    Gson gson = new Gson();
    Bookmark bookmark = gson.fromJson(body, Bookmark.class);
    System.out.println(bookmark.getClass().getName()); // -> models.Bookmark    
    bookmark.save(); 

但我认为我做错了什么，因为这段代码引发了以下异常:

Execution exception (In /app/controllers/Bookmarks.java around line 40)
IllegalArgumentException occured : can't serialize class java.lang.Object

play.exceptions.JavaExecutionException: can't serialize class java.lang.Object
    at play.mvc.ActionInvoker.invoke(ActionInvoker.java:231)
    at Invocation.HTTP Request(Play!)
Caused by: java.lang.IllegalArgumentException: can't serialize class java.lang.Object
    at org.bson.BSONEncoder._putObjectField(BSONEncoder.java:234)
    at org.bson.BSONEncoder.putIterable(BSONEncoder.java:259)
    at org.bson.BSONEncoder._putObjectField(BSONEncoder.java:198)
    at org.bson.BSONEncoder.putObject(BSONEncoder.java:140)
    at org.bson.BSONEncoder.putObject(BSONEncoder.java:86)
    at com.mongodb.OutMessage.putObject(OutMessage.java:190)
    at com.mongodb.DBApiLayer$MyCollection.insert(DBApiLayer.java:253)
    at com.mongodb.DBApiLayer$MyCollection.insert(DBApiLayer.java:217)
    at com.mongodb.DBCollection.insert(DBCollection.java:71)
    at com.mongodb.DBCollection.save(DBCollection.java:633)
    at com.google.code.morphia.DatastoreImpl.save(DatastoreImpl.java:764)
    at com.google.code.morphia.DatastoreImpl.save(DatastoreImpl.java:826)
    at com.google.code.morphia.DatastoreImpl.save(DatastoreImpl.java:820)
    at play.modules.morphia.Model.save2(Model.java:705)
    at play.modules.morphia.Model.save(Model.java:692)
    at controllers.Bookmarks.add(Bookmarks.java:40)
    at play.mvc.ActionInvoker.invokeWithContinuation(ActionInvoker.java:548)
    at play.mvc.ActionInvoker.invoke(ActionInvoker.java:502)
    at play.mvc.ActionInvoker.invokeControllerMethod(ActionInvoker.java:478)
    at play.mvc.ActionInvoker.invokeControllerMethod(ActionInvoker.java:473)
    at play.mvc.ActionInvoker.invoke(ActionInvoker.java:161)
    ... 1 more

似乎以下行抛出了此异常:

bookmark.save();

这是模型的代码:

@AutoTimestamp
@Entity
public class Bookmark extends Model {
    public String title;
    public String url;
    public String description;
    @Indexed
    public List tags;
    public boolean is_private;

    public Bookmark() {}

    public Bookmark(String title,
                    String url,
                    String description,
                    List tags,
                    boolean is_private)
    {
        this.title          = title;
        this.url            = url;
        this.description    = description;
        this.tags           = tags;
        this.is_private     = is_private;
    }
}

我现在的问题是如何解决这个问题，或者如何根据 json 输入创建模型实例？

Answer 1

它抛出一个错误，因为 fromJson()仅接受 String 或 Reader 对象，您传入的是 JsonObject。

但是因为玩!使用POJO binding最好这样做:

public static void add(Bookmark newBookmark) {  
    // Validation etc ..
    bookmark.save(); 
}

如果你真的想使用 Gson 那么这样的东西可能会起作用(基于查看 the docs ):

public static void add(JsonObject body) {  
    Gson gson = new Gson();
    String json = gson.toJson(body, Bookmark.class);
    Bookmark bookmark = gson.fromJson(json, Bookmark.class);
    bookmark.save(); 
}