用JSON写文章时的奇怪ExecutionException

Question

我有这样的方法：

/**
 * POST
 */
public static void create(String body) {
    Logger.info("APPOINTMENT create - json string: %s", body);

    Appointment appointment = null;
    try {
        appointment = new Gson().fromJson(body, Appointment.class);

        //services are detached, re-take them from db
        List<Service> refreshedServices = new ArrayList<Service>();
        for (final Service ser : appointment.services) {
            Service service = Service.findById(ser.id);
            refreshedServices.add(service);
        }
        appointment.services = refreshedServices;
        appointment.save();
        appointment.refresh();
        Logger.info("services refreshed");
    } catch (Exception ex) {
        Logger
                .info(
                        "An error has occured when trying to create an APPOINTMENT %s",
                        ex);
        response.status = Http.StatusCode.INTERNAL_ERROR;
        renderJSON(new StatusMessage(
                "An internal error has occured. Please try again later."));
    }

    renderJSON(appointment);
}

我是这样测试的：

public void createAppointment(final Contact contact, final List<Service> services) throws Exception {
        Appointment app = new Appointment();
        app.userUid = "cristi-uid";
        app.name = "app1";
        app.contact = contact;

        String serviceAsJson = "{\"userUid\":\"cristi-uid\",\"name\":\"app1\",\"allDay\":false,\"contact\":{\"id\":"+contact.id+"},\"services\":[{\"id\":\""+services.get(0).getId()+"\"},{\"id\":\""+services.get(1).getId()+"\"}]}";
        Response response = POST("/appointment/create", "application/json", serviceAsJson);

        Logger.info("POST was done");
        Appointment appReturned = new Gson().fromJson(response.out.toString(), Appointment.class);

        Logger.info("appointment create response: %s", response.out.toString());

        assertIsOk(response);
        assertEquals(appReturned.name, app.name);
    }

问题是它抛出了这个例外：

java.lang.RuntimeException: java.util.concurrent.ExecutionException: play.exceptions.JavaExecutionException
at play.test.FunctionalTest.makeRequest(FunctionalTest.java:304)
at play.test.FunctionalTest.makeRequest(FunctionalTest.java:310)
at play.test.FunctionalTest.POST(FunctionalTest.java:152)
at play.test.FunctionalTest.POST(FunctionalTest.java:120)
at play.test.FunctionalTest.POST(FunctionalTest.java:116)
at AppointmentsTest.createAppointment(AppointmentsTest.java:61)

我也找不出原因。

它打印出Logger.info("services refreshed");之后，它抛出了异常.

你们看到这个测试柱出什么问题了吗？

UPDATE：似乎这些问题来自试图将appointment呈现为JSON：

Caused by: java.lang.StackOverflowError
at java.util.LinkedHashMap$LinkedHashIterator.(LinkedHashMap.java:345)
at java.util.LinkedHashMap$LinkedHashIterator.(LinkedHashMap.java:345)
at java.util.LinkedHashMap$ValueIterator.(LinkedHashMap.java:387)
at java.util.LinkedHashMap$ValueIterator.(LinkedHashMap.java:387)
at java.util.LinkedHashMap.newValueIterator(LinkedHashMap.java:397)
at java.util.HashMap$Values.iterator(HashMap.java:910)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:192)
at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:879)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)

Answer 1

我能够通过深入研究错误跟踪来识别问题。基本上，我的Appointment对象有一些ManyToMany关系，在试图呈现这些关系时，renderJSON似乎给出了StackOverFlow。

我已经创建了另一个Appointment对象，并且只将需要导出的字段复制到其中。

    Appointment appointmentOutput = new Appointment();
    appointmentOutput.id = appointment.id;
    appointmentOutput.name = appointment.name;

    renderJSON(appointmentOutput);

Answer 2

这是因为：

Play框架与Google的JSON库Gson捆绑在一起，但是这个库的开发人员已经做出了一些设计选择，这使得它无法理想地生成将要发送到HTTP客户端的JSON。

Erik 推荐使用FlexSon