Spring 和 Jackson 在异常后返回状态为 200 OK 但 JSON 不正确的响应

Question

我有一个简单的控制器，它返回MyClass1的一个实例。 MyClass1包含MyClass2的列表，并使用@JsonDeserialize注释告诉Jackson使用自定义序列化程序“MySerializer”。

public class MyClass1 {

    @JsonSerialize(contentUsing = MySerializer.class)
    private List<MyClass2> class2;

    public List<MyClass2> getClass2() {
        return class2;
    }

    public void setClass2(List<MyClass2> propertyTest2) {
        this.class2 = propertyTest2;
    }

}

public class MyClass2 {

    private String myString;

    public String getMyString() {
        return myString;
    }

    public void setMyString(String myString) {
        this.myString = myString;
    }
}

public class MySerializer extends StdSerializer<MyClass2> {

    public MySerializer() {
        this(null);
    }

    protected MySerializer(Class<MyClass2> t) {
        super(t);
    }

    @Override
    public void serialize(MyClass2 value, JsonGenerator gen, SerializerProvider provider) throws IOException {
        gen.writeStartObject();
        gen.writeObjectField("myObject", value);
        gen.writeEndObject();
    }

}

@RestController
public class MyController {

    @GetMapping(value = "/api", produces = "application/json;charset=UTF-8")
    public MyClass1 myMethod() {

        MyClass1 class1 = new MyClass1();
        MyClass2 class2 = new MyClass2();
        class2.setMyString("test string");
        List<MyClass2> class2List = new ArrayList<>();
        class2List.add(class2);
        class1.setClass2(class2List);

        return class1;
    }

}

因此，每当我向 /api 发送获取请求时，使用此代码都会得到响应：

{
    "class2": [
        {
            "myObject": {
                "myString": "test string"
            }
        }
    ]
}

但是，如果我更新 MyClass1 的代码并添加属性 errorProperty 以引发异常：

public class MyClass1 {

    @JsonSerialize(contentUsing = MySerializer.class)
    private List<MyClass2> class2;

    public List<MyClass2> getClass2() {
        return class2;
    }

    public void setClass2(List<MyClass2> propertyTest2) {
        this.class2 = propertyTest2;
    }

    public int getMyError() {
        String error = null;
        error.toLowerCase();
        return 1;
    }
}

我从Spring Boot收到以下响应（状态为 200 OK）：

{
    "class2": [
        {
            "myObject": {
                "myString": "test string"
            }
        }
    ]
}{
    "timestamp": "2022-05-11T16:55:09.312+00:00",
    "status": 200,
    "error": "OK",
    "path": "/api"
}

我想了解为什么我会收到 200 ok 的响应，因为自从引发异常以来，我预计会出现 500 个内部服务器错误。 而且响应中有 2 个 json，所以我认为这不是正确的响应。 这是我使用@JsonSerialize 功能的方式的问题还是来自jackson 的错误。

这里也是堆栈跟踪：

java.lang.NullPointerException: null
    at com.example.test_spring.serializeronproperty.MyClass1.getMyError(MyClass1.java:22) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_291]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_291]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_291]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_291]
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:689) ~[jackson-databind-2.13.2.1.jar:2.13.2.1]
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:774) ~[jackson-databind-2.13.2.1.jar:2.13.2.1]
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:178) ~[jackson-databind-2.13.2.1.jar:2.13.2.1]
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480) ~[jackson-databind-2.13.2.1.jar:2.13.2.1]
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319) ~[jackson-databind-2.13.2.1.jar:2.13.2.1]
    at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1518) ~[jackson-databind-2.13.2.1.jar:2.13.2.1]
    at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:1007) ~[jackson-databind-2.13.2.1.jar:2.13.2.1]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:456) ~[spring-web-5.3.19.jar:5.3.19]
    at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:104) ~[spring-web-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:290) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:183) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:78) ~[spring-web-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:135) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:655) ~[tomcat-embed-core-9.0.62.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.19.jar:5.3.19]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) ~[tomcat-embed-core-9.0.62.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.19.jar:5.3.19]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.19.jar:5.3.19]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.19.jar:5.3.19]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.19.jar:5.3.19]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.19.jar:5.3.19]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.19.jar:5.3.19]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1743) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.62.jar:9.0.62]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_291]

Answer 1

您使用@JsonSerialize的方式很好，不会导致您的问题。

如果您在模型对象之外的某个地方（例如控制器）强制NullPointerException ，Spring Boot 将返回您期望的序列化 500 错误响应，但您看到的奇怪行为是由于您的 getter 中的逻辑。 只需将该逻辑移出您的 getter 即可获得您的预期结果。

当 spring-webmvc 的ServletInvocableHandlerMethod的invokeAndHandle()方法尝试序列化MyClass1并且无法解决在其getMyError()方法中强制执行的NullPointerException时，会发生这种奇怪的行为。

在处理webRequest期间没有引发异常，因此它使用 200 OK 响应序列化响应。 我相信正在做出一个假设，即正在使用最佳实践并且响应可以在不满足任何逻辑的情况下自行执行，因为我们应该在没有进一步处理逻辑的情况下处理模型对象（在典型的 getter 和 setter 之外）。 在此响应的序列化过程中，Jackson 在 getter 中发现了意外的逻辑，并引发了异常（未预料到的异常），从而导致了奇怪的行为。 我相信 spring-boot 然后拦截异常并将其序列化并将其附加到响应中。