Spring 和 Jackson 在異常后返回狀態為 200 OK 但 JSON 不正確的響應

Question

我有一個簡單的控制器，它返回MyClass1的一個實例。 MyClass1包含MyClass2的列表，並使用@JsonDeserialize注釋告訴Jackson使用自定義序列化程序“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，每當我向 /api 發送獲取請求時，使用此代碼都會得到響應：

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

但是，如果我更新 MyClass1 的代碼並添加屬性 errorProperty 以引發異常：

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;
    }
}

我從Spring Boot收到以下響應（狀態為 200 OK）：

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

我想了解為什么我會收到 200 ok 的響應，因為自從引發異常以來，我預計會出現 500 個內部服務器錯誤。 而且響應中有 2 個 json，所以我認為這不是正確的響應。 這是我使用@JsonSerialize 功能的方式的問題還是來自jackson 的錯誤。

這里也是堆棧跟蹤：

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，不會導致您的問題。

如果您在模型對象之外的某個地方（例如控制器）強制NullPointerException ，Spring Boot 將返回您期望的序列化 500 錯誤響應，但您看到的奇怪行為是由於您的 getter 中的邏輯。 只需將該邏輯移出您的 getter 即可獲得您的預期結果。

當 spring-webmvc 的ServletInvocableHandlerMethod的invokeAndHandle()方法嘗試序列化MyClass1並且無法解決在其getMyError()方法中強制執行的NullPointerException時，會發生這種奇怪的行為。

在處理webRequest期間沒有引發異常，因此它使用 200 OK 響應序列化響應。 我相信正在做出一個假設，即正在使用最佳實踐並且響應可以在不滿足任何邏輯的情況下自行執行，因為我們應該在沒有進一步處理邏輯的情況下處理模型對象（在典型的 getter 和 setter 之外）。 在此響應的序列化過程中，Jackson 在 getter 中發現了意外的邏輯，並引發了異常（未預料到的異常），從而導致了奇怪的行為。 我相信 spring-boot 然后攔截異常並將其序列化並將其附加到響應中。