java - Rest Web 服务不返回 XML 响应，甚至在 Eclipse 中没有登录控制台

Question

创建一个安静的应用程序，但它没有以 XML 形式返回响应。即使点击 URL“http://localhost:8080/message/webapi/messages ”，控制台也没有登录。

我返回一个列表并使用 @Produces(MediaType.APPLICATION_XML) 返回 XML 格式的响应。

MessageResource.java

package org.porwal.restful.message.resources;

import java.util.List;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

import org.porwal.restful.message.model.Message;
import org.porwal.restful.message.service.MessageService;

@Path("/messages")
public class MessageResource {

    MessageService ms = new MessageService();

    @GET
    @Produces(MediaType.APPLICATION_XML)
    public List<Message> getMessage(){
        return ms.getAllMessage();
    }

}

Message.java

package org.porwal.restful.message.model;

import java.util.Date;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement( name = "Message" )
public class Message {

    public long id;
    public String message;
    public Date created;
    public String author;

    public Message() {

    }

    public Message(long id, String message, String author) {
        this.id = id;
        this.message = message;
        this.author = author;
        this.created = new Date();
    }

    public long getId() {
        return id;
    }
    @XmlElement (name = "ID")
    public void setId(long id) {
        this.id = id;
    }
    public String getMessage() {
        return message;
    }
    @XmlElement (name = "Message")
    public void setMessage(String message) {
        this.message = message;
    }
    public Date getCreated() {
        return created;
    }
    @XmlElement (name = "Created")
    public void setCreated(Date created) {
        this.created = created;
    }
    public String getAuthor() {
        return author;
    }
    @XmlElement (name = "Author")
    public void setAuthor(String author) {
        this.author = author;
    }

}

如果我不使用 @XMLRootElement 注释并且 TEXT_PLAIN 通过 URL 很好地返回，那么这是有效的。我还尝试删除每个字段的 @XmlElement 但没有成功。当我删除 @XMLRootElement 时，可以在 Eclipse 控制台的日志中看到 MessageBodyWriter 错误，但是当包含 @XMLRootElement 时，Eclipse 控制台上没有日志，并且 URL“http://localhost:8080/message/webapi/messages ”会引发错误:

缺少 @XmlRootElement 时出错。

org.glassfish.jersey.message.internal.WriterInterceptorExecutor$TerminalWriterInterceptor aroundWriteTo SEVERE: MessageBodyWriter not found for media type=application/xml, type=class java.util.ArrayList, genericType=java.util.List<org.porwal.restful.message.model.Message>. This exception comes only when i commented the line "//@XmlRootElement( name = "Message" )".

HTTP 状态 500 – 内部服务器错误

有人可以告诉我这里缺少什么吗？

Answer 1

您需要将 Message 类中的所有字段设为私有(private)。如果您将它们保留为公共(public)，那么 JAXB 会将其视为属性，并将其视为重复属性，因为您也有 JavaBean 属性(getter/setter)。

@XmlRootElement( name = "Message" )
public class Message {

    private long id;
    private String message;
    private Date created;
    private String author;

    // ...
}

<小时/>

我是如何通过使用通用的ExceptionMapper

来解决这个问题的

@Provider
public class DebugExceptionMapper implements ExceptionMapper<Exception> {

    @Override
    public Response toResponse(Exception exception) {
        exception.printStackTrace();
        return Response.serverError().entity(exception.getMessage()).build();
    } 
}

您可以在您的应用程序中注册它，它会捕获未映射的异常，您可以用它做任何您想做的事情。这里我们只打印堆栈跟踪。如果我们不处理它，它就会被吞没，我们永远不知道发生了什么。

使用 ExceptionMapper 运行应用程序时，这是我收到的错误消息。

Caused by: com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 4 counts of IllegalAnnotationExceptions
Class has two properties of the same name "author"
    this problem is related to the following location:
        at public java.lang.String com.example.Message.getAuthor()
        at com.example.Message
    this problem is related to the following location:
        at public java.lang.String com.example.Message.author
        at com.example.Message
Class has two properties of the same name "created"
    this problem is related to the following location:
        at public java.util.Date com.example.Message.getCreated()
        at com.example.Message
    this problem is related to the following location:
        at public java.util.Date com.example.Message.created
        at com.example.Message
Class has two properties of the same name "id"
    this problem is related to the following location:
        at public long com.example.Message.getId()
        at com.example.Message
    this problem is related to the following location:
        at public long com.example.Message.id
        at com.example.Message
Class has two properties of the same name "message"
    this problem is related to the following location:
        at public java.lang.String com.example.Message.getMessage()
        at com.example.Message
    this problem is related to the following location:
        at public java.lang.String com.example.Message.message
        at com.example.Message

你可以清楚地看到问题所在。除了避免这个错误之外，封装应该是这样工作的；这些字段应该是私有(private)的，并通过 getter 和 setter 公开。