Java 尝试将自定义对象转换为json时出现异常

在你们将这个问题标记为重复问题之前，我想告诉你们，我已经尝试了来自的解决方案

而我仍然被困住了。这是我的一个例外

24-Apr-2016 02:03:00.655 SEVERE [http-nio-8080-exec-1] com.sun.jersey.spi.container.ContainerResponse.write A message body writer for Java class com.upwork.magnus.model.FirstException, and Java type class com.upwork.magnus.model.FirstException, and MIME media type application/json was not found
24-Apr-2016 02:03:00.656 SEVERE [http-nio-8080-exec-1] com.sun.jersey.spi.container.ContainerResponse.write The registered message body writers compatible with the MIME media type are:
*/* ->
  com.sun.jersey.core.impl.provider.entity.FormProvider
  com.sun.jersey.core.impl.provider.entity.StringProvider
  com.sun.jersey.core.impl.provider.entity.ByteArrayProvider
  com.sun.jersey.core.impl.provider.entity.FileProvider
  com.sun.jersey.core.impl.provider.entity.InputStreamProvider
  com.sun.jersey.core.impl.provider.entity.DataSourceProvider
  com.sun.jersey.core.impl.provider.entity.XMLJAXBElementProvider$General
  com.sun.jersey.core.impl.provider.entity.ReaderProvider
  com.sun.jersey.core.impl.provider.entity.DocumentProvider
  com.sun.jersey.core.impl.provider.entity.StreamingOutputProvider
  com.sun.jersey.core.impl.provider.entity.SourceProvider$SourceWriter
  com.sun.jersey.server.impl.template.ViewableMessageBodyWriter
  com.sun.jersey.core.impl.provider.entity.XMLRootElementProvider$General
  com.sun.jersey.core.impl.provider.entity.XMLListElementProvider$General

24-Apr-2016 02:03:00.656 SEVERE [http-nio-8080-exec-1] com.sun.jersey.spi.container.ContainerResponse.logException Mapped exception to response: 500 (Internal Server Error)
 javax.ws.rs.WebApplicationException: com.sun.jersey.api.MessageException: A message body writer for Java class com.upwork.magnus.model.FirstException, and Java type class com.upwork.magnus.model.FirstException, and MIME media type application/json was not found
    at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:285)
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1437)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1349)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1339)
    at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:537)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:699)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:522)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1095)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:672)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)
Caused by: com.sun.jersey.api.MessageException: A message body writer for Java class com.upwork.magnus.model.FirstException, and Java type class com.upwork.magnus.model.FirstException, and MIME media type application/json was not found
    ... 29 more

下面是

pom.xml

文件依赖项文件

<dependencies>
    <dependency>
        <groupId>com.sun.jersey</groupId>
        <artifactId>jersey-server</artifactId>
        <version>1.8</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.9</version>
    </dependency>
    <dependency>
        <groupId>org.eclipse.persistence</groupId>
        <artifactId>eclipselink</artifactId>
        <version>2.5.0</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
        <version>2.5</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
    </dependency>
    <dependency>
        <groupId>com.sun.jersey</groupId>
        <artifactId>jersey-json</artifactId>
        <version>1.9.1</version>
    </dependency>
    <dependency>
        <groupId>joda-time</groupId>
        <artifactId>joda-time</artifactId>
        <version>2.9.1</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.7.0</version>
    </dependency>
    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-core-asl</artifactId>
        <version>1.9.9</version>
    </dependency>
    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-jaxrs</artifactId>
        <version>1.9.9</version>
    </dependency>
    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-mapper-asl</artifactId>
        <version>1.9.9</version>
    </dependency>
    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-xc</artifactId>
        <version>1.9.9</version>
    </dependency>

    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>
</dependencies>

fe

对象的类型为

FirstException

。这是那门课

public class FirstException implements Serializable{
    private int errorCode;
    private String message;

    public FirstException(int errorCode, String message) {
        this.errorCode = errorCode;
        this.message = message;
    }

    public String getMessage() {
        return message;
    }

    public int getErrorCode() { return errorCode;}
}

这是我配置pojo的web.xml部分

<servlet>
    <servlet-name>jersey-servlet</servlet-name>
    <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
    <init-param>
        <param-name>com.sun.jersey.config.property.packages</param-name>
        <param-value>com.upwork.magnus.api</param-value>
    </init-param>
    <init-param>
        <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
        <param-value>true</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

---

如果查看该错误，您将看到Jackson json提供程序不是已注册的提供程序之一。只有默认的Jersey是，它使用JAXB功能。因此，您可以使用

@XmlRootElement

注释

FirstException

类，它应该可以工作。但是，围绕根本问题，这确实是一项不可取的工作，即“为什么没有使用Jackson？”

确保使用Jackson的方法是将

org.codehaus.Jackson.jaxrs

包添加到要扫描的包列表中。此包包含Jackson json提供程序

<init-param>
    <param-name>com.sun.jersey.config.property.packages</param-name>
    <param-value>
        com.upwork.magnus.api,
        org.codehaus.jackson.jaxrs
    </param-value>
</init-param>

com.sun.jersey.config.property.packages
com.upwork.magnus.api，
org.codehaus.jackson.jaxrs

为什么FlightException不是异常子类？对不起，这正是我使用的名称。最有可能的情况是，它将被更改为

ErrorResponse

jersey json

拉入您需要的Jackson。你无缘无故地拥有所有不同版本的不同内容。删除并尝试。同样的问题。我将在我的问题中发布更新的pom.xml。感谢您可以将

@XmlRootElement

添加到

FirstException

类中。它应该会起作用。但这确实是一个不希望解决的根本问题，即“为什么杰克逊没有被使用”。查看错误，如果您查看提供商列表，您不会看到Jackson。我不知道为什么。

<dependencies>
    <dependency>
        <groupId>com.sun.jersey</groupId>
        <artifactId>jersey-server</artifactId>
        <version>1.8</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.9</version>
    </dependency>
    <dependency>
        <groupId>org.eclipse.persistence</groupId>
        <artifactId>eclipselink</artifactId>
        <version>2.5.0</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
        <version>2.5</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
    </dependency>
    <dependency>
        <groupId>com.sun.jersey</groupId>
        <artifactId>jersey-json</artifactId>
        <version>1.9.1</version>
    </dependency>
    <dependency>
        <groupId>joda-time</groupId>
        <artifactId>joda-time</artifactId>
        <version>2.9.1</version>
    </dependency>

<init-param>
    <param-name>com.sun.jersey.config.property.packages</param-name>
    <param-value>
        com.upwork.magnus.api,
        org.codehaus.jackson.jaxrs
    </param-value>
</init-param>