将 Gson 与接口类型结合使用

我正在编写一些服务器代码，其中客户端以 JSON 形式发送请求。我的问题是，有许多可能的请求，所有请求在小的实现细节上都有所不同。 因此我想到使用 Request 接口，定义为：

public interface Request {
    Response process ( );
}

从那里，我在一个名为的类中实现了该接口LoginRequest如图所示：

public class LoginRequest implements Request {
    private String type = "LOGIN";
    private String username;
    private String password;

    public LoginRequest(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getType() {
        return type;
    }
    public void setType(String type) {
        this.type = type;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }

    /**
     * This method is what actually runs the login process, returning an
     * appropriate response depending on the outcome of the process.
     */
    @Override
    public Response process() {
        // TODO: Authenticate the user - Does username/password combo exist
        // TODO: If the user details are ok, create the Player and add to list of available players
        // TODO: Return a response indicating success or failure of the authentication
        return null;
    }

    @Override
    public String toString() {
        return "LoginRequest [type=" + type + ", username=" + username
            + ", password=" + password + "]";
    }
}

为了使用 JSON，我创建了一个GsonBuilder实例并注册了一个InstanceCreator如图所示：

public class LoginRequestCreator implements InstanceCreator<LoginRequest> {
    @Override
    public LoginRequest createInstance(Type arg0) {
        return new LoginRequest("username", "password");
    }
}

然后我使用它，如下面的代码片段所示：

GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(LoginRequest.class, new LoginRequestCreator());
Gson parser = builder.create();
Request request = parser.fromJson(completeInput, LoginRequest.class);
System.out.println(request);

我得到了预期的输出。

我想做的就是更换线路Request request = parser.fromJson(completeInput, LoginRequest.class);与类似的东西Request request = parser.fromJson(completeInput, Request.class);但这样做是行不通的，因为Request是一个接口。

我想要我的Gson根据收到的 JSON 返回适当类型的请求。

我传递给服务器的 JSON 示例如下所示：

{
    "type":"LOGIN",
    "username":"someuser",
    "password":"somepass"
}

重申一下，我正在寻找一种方法来解析来自客户端的请求（以 JSON 形式）并返回实现Request界面

如果没有一定程度的自定义编码，则所描述类型的多态映射在 Gson 中不可用。有一个扩展型适配器可用作为额外的 https://github.com/google/gson/blob/master/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java它提供了您正在寻找的大量功能，但需要注意的是，需要提前向适配器声明多态子类型。下面是它的使用示例：

public interface Response {}

public interface Request {
    public Response process();
}

public class LoginRequest implements Request {
    private String userName;
    private String password;

    // Constructors, getters/setters, overrides
}

public class PingRequest implements Request {
    private String host;
    private Integer attempts;

    // Constructors, getters/setters, overrides
}

public class RequestTest {

    @Test
    public void testPolymorphicSerializeDeserializeWithGSON() throws Exception {
        final TypeToken<List<Request>> requestListTypeToken = new TypeToken<List<Request>>() {
        };

        final RuntimeTypeAdapterFactory<Request> typeFactory = RuntimeTypeAdapterFactory
                .of(Request.class, "type")
                .registerSubtype(LoginRequest.class)
                .registerSubtype(PingRequest.class);

        final Gson gson = new GsonBuilder().registerTypeAdapterFactory(
                typeFactory).create();

        final List<Request> requestList = Arrays.asList(new LoginRequest(
                "bob.villa", "passw0rd"), new LoginRequest("nantucket.jones",
                "crabdip"), new PingRequest("example.com", 5));

        final String serialized = gson.toJson(requestList,
                requestListTypeToken.getType());
        System.out.println("Original List: " + requestList);
        System.out.println("Serialized JSON: " + serialized);

        final List<Request> deserializedRequestList = gson.fromJson(serialized,
                requestListTypeToken.getType());

        System.out.println("Deserialized list: " + deserializedRequestList);
    }
}

请注意，您实际上不需要定义type各个 Java 对象的属性 - 它仅存在于 JSON 中。