如何从泽西REST API方法返回响应，该方法内部有列表器

Question

我正在尝试创建REST api，以使用Firebase Server SDK和Jersey执行写入操作。

以下是我要做的：

1. 初始化Firebase SDK
2. 从客户端获取idToken并验证idToken
3. 在少数Firebase节点上执行一些写入操作
4. 发送api响应

我只想在Firebase写入操作成功或失败时返回Response。这发生在Firebase Listeners内部。然而，我尝试从侦听器返回值，但由于Firebase侦听器具有void返回类型，所以收到错误消息。

我如何从监听器返回响应？

这是我的代码。

MyEndpoint.java

@Path("/restapi")
//BaseEndpoint does Authentication operations
public class MyEndpoint extends BaseEndpoint {

    public void Authenticate(String token, AuthenticationListener authenticationResultListener) {
        super.Authenticate(token, authenticationResultListener);
    }

    @POST
    @Produces("application/json")
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    public Response createCommunity(@FormParam("idToken") String idToken) {
        Authenticate(idToken, new AuthenticationListener() {
            @Override
            public void onAuthenticationSuccess() {
                // The app only has access as defined in the Security Rules
                DatabaseReference ref = FirebaseDatabase.getInstance().getReference("/mysamplenode");
                ref.addListenerForSingleValueEvent(new ValueEventListener() {
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        String res = dataSnapshot.getKey();
                        //I will do some write operations on Firebase here
                        //If they complete successfuly only then I want to return api response
                        return Response.status(200).entity().build();
                    }
                    @Override
                    public void onCancelled(DatabaseError arg0) {
                        System.out.println("DatabaseError-------------" + arg0);
                        return Response.status(500).entity("DatabaseError").build();
                    }
                });
            }
            @Override
            public void onAuthenticationFailure() {
                return Response.status(403).entity("Forbidden").build();
            }
        });
    }
}

BaseEndpoint.java

    public class BaseEndpoint {

    public static String uid;

    public void Authenticate(String token, AuthenticationListener authenticationResultListener) {
        // idToken comes from the client app
        FirebaseAuth.getInstance().verifyIdToken(token).addOnFailureListener(new OnFailureListener() {

            @Override
            public void onFailure(Exception arg0) {
                System.out.println("Uid exp= " + arg0);
                authenticationResultListener.onAuthenticationFailure();
            }
        }).addOnSuccessListener(new OnSuccessListener<FirebaseToken>() {
            @Override
            public void onSuccess(FirebaseToken decodedToken) {
                uid = decodedToken.getUid();
                System.out.println("Uid= " + uid);
                authenticationResultListener.onAuthenticationSuccess();
            }
        });
    }
}

Answer 1

我回答这个问题可能有点晚，但在试用Firebase服务器SDK后，我发现您可以在SDK中创建一个可用的任务以同步等待响应。下面的片段可能会对您有所帮助：

public class BaseEndpoint {

    public static String uid;

    public void Authenticate(String token, AuthenticationListener authenticationResultListener) {
        // idToken comes from the client app
        FirebaseToken firebaseToken = null;
        try {
            Task<FirebaseToken> authTask = FirebaseAuth.getInstance().verifyIdToken(token);
            Tasks.await(authTask);
            firebaseToken = authTask.getResult();
        } catch (Exception e) {
            authenticationResultListener.onAuthenticationFailure();
        }
        uid = firebaseToken.getUid();
        System.out.println("Uid= " + uid);
        authenticationResultListener.onAuthenticationSuccess();
    }
}

Answer 2

所以我猜测Firebase SDK本质上是异步的。在这种情况下，如果您使用的是Jersey 2.x，则可以使用异步服务器支持。您只需调用AsyncResponse。恢复（响应）。例如

@POST
@Produces("application/json")
@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
public void createCommunity(@FormParam("idToken") String idToken,
                                @Suspended final AsyncResponse response) {
    Authenticate(idToken, new AuthenticationListener() {
        @Override
        public void onAuthenticationSuccess() {
            DatabaseReference ref = FirebaseDatabase.getInstance()
                    .getReference("/mysamplenode");
            ref.addListenerForSingleValueEvent(new ValueEventListener() {
                public void onDataChange(DataSnapshot dataSnapshot) {
                    String res = dataSnapshot.getKey();                        
                    response.resume(Response.status(200).entity().build());
                }
                @Override
                public void onCancelled(DatabaseError arg0) {
                    response.resume(Response.status(500).entity("DatabaseError").build());
                }
            });
        }
        @Override
        public void onAuthenticationFailure() {
            response.resume(Response.status(403).entity("Forbidden").build());
        }
    });
}

如果你使用的是Jersey 1.x，实际上没有异步选项。您只需要用< code>CountDownLatch阻塞流，在回调中分配一个本地< code>Response，然后递减计数。

@POST
@Produces("application/json")
@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
public void createCommunity(@FormParam("idToken") String idToken) {
    Response response;
    CountDownLatch latch = new CountDownLatch(1);
    Authenticate(idToken, new AuthenticationListener() {
        @Override
        public void onAuthenticationSuccess() {
            DatabaseReference ref = FirebaseDatabase.getInstance()
                    .getReference("/mysamplenode");
            ref.addListenerForSingleValueEvent(new ValueEventListener() {
                public void onDataChange(DataSnapshot dataSnapshot) {
                    String res = dataSnapshot.getKey();                        
                    response = Response.status(200).entity().build();
                    latch.countDown();
                }
                @Override
                public void onCancelled(DatabaseError arg0) {
                    response = Response.status(500).entity("DatabaseError").build();
                    latch.countDown();
                }
            });
        }
        @Override
        public void onAuthenticationFailure() {
            response = Response.status(403).entity("Forbidden").build();
            latch.countDown();
        }
    });
    latch.await();
    return response;
}