用Jackson以两种不同的方式序列化一个班级 [英] Serialize one class in two different ways with Jackson

问题描述

在我们的一个项目中，我们使用java webapp与MongoDB实例进行通信。在数据库中，我们使用 DBRefs 来跟踪一些对象关系。我们使用jackson（使用mongodb-jackson-mapper）使用POJO对象进行序列化。

In one of our projects we use a java webapp talking to a MongoDB instance. In the database, we use DBRefs to keep track of some object relations. We (de)serialize with POJO objects using jackson (using mongodb-jackson-mapper).

然而，我们使用相同的POJO然后（de）序列化到外部世界，我们的前端处理呈现JSON。

However, we use the same POJOs to then (de)serialize to the outside world, where our front end deals with presenting the JSON.

现在，我们需要一种方法让外部世界的序列化包含来自<$ c的引用对象$ c> DBRef （这样UI可以呈现完整的对象），而我们显然希望将 DBRef 写入数据库，并且不是整个对象。

Now, we need a way for the serialization for the outside world to contain the referenced object from a DBRef (so that the UI can present the full object), while we obviously want to have the DBRef written to the database, and not the whole object.

现在我写了一些未经测试的静态嵌套类代码：

Right now I wrote some untested static nested class code:

public static class FooReference {
    public DBRef<Foo> foo;

    // FIXME how to ensure that this doesn't go into the database?
    public Foo getFoo() {
        return foo.fetch();
    }
}

理想情况下我想要一种方法来注释这个我可以使用或不使用getFoo（）结果（de）序列化它，可能取决于某些配置对象。这可能吗？你看到了更好的方法吗？

Ideally I would like a way to annotate this so that I could (de)serialize it either with or without the getFoo() result, probably depending on some configuration object. Is this possible? Do you see a better way of going about doing this?

推荐答案

从查看选项看，你似乎只能注释属性如果将给定的 View 传递给用于序列化的 ObjectMapper ，则显示。因此，您可以编辑该类：

From looking at options, it seems you can annotate properties to only be shown if a given View is passed to the ObjectMapper used for serialization. You could thus edit the class:

public static class FooReference {
    public DBRef<Foo> foo;

    @JsonView(Views.WebView.class)
    public Foo getFoo() {
        return foo.fetch();
    }
}

并提供：

class Views {
    static class WebView { }
}

然后在创建具有正确视图的配置后序列化：

and then serialize after creating a configuration with the correct view:

SerializationConfig conf = objectMapper.getSerializationConfig().withView(Views.WebView.class);
objectMapper.setSerializationConfig(conf);

然后将序列化它。使用MongoDB包装器进行序列化时不指定视图意味着该方法将被忽略。默认情况下，没有JsonView注释的属性会被序列化，您可以通过指定以下内容来更改该行为：

Which would then serialize it. Not specifying the view when serializing with the MongoDB wrapper would mean the method would be ignored. Properties without a JsonView annotation are serialized by default, a behaviour you can change by specifying:

objectMapper.configure(SerializationConfig.Feature.DEFAULT_VIEW_INCLUSION, false);

有更多信息。

More info is available on the Jackson Wiki.

还有其他选择，事实证明： Jackson MixIns ，它允许你覆盖（de）类的部分行为而不修改类本身，以及Jackson 2.0（最近发布的）也有过滤器。

There are still other alternatives, too, it turns out: there are Jackson MixIns which would let you override (de)serialization behaviour of parts of a class without modifying the class itself, and as of Jackson 2.0 (very recent release) there are filters, too.

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