Java REST API：返回 ArrayList<T> 作为 JSON 响应问题
Java REST API: Returning ArrayList<T> as a JSON Response Issue
我需要简单地 return 对象的 ArrayList 作为我的 Rest API 响应，但我不断收到此错误：
A message body writer for Java class
java.util.Collections$SingletonList and MIME media type
application/json was not found.
我的代码：
@Path("/plans")
public class PlanAPI {
@GET
@Produces(MediaType.APPLICATION_JSON)
@Path("/getplans/{type}")
public Response GetAllPlans(@PathParam("type") String type) {
PlanDAO dao = new PlanDAO();
ArrayList<UserPlan> plans = dao.GetAllPlans_ByType(type);
return Response.status(200).entity(plans).build();
}
}
我得到的错误：
com.sun.jersey.spi.container.ContainerResponse logException
SEVERE: Mapped exception to response: 500 (Internal Server Error)
javax.ws.rs.WebApplicationException: com.sun.jersey.api.MessageException: A message body writer for Java class java.util.Collections$SingletonList, and Java type java.util.List<java.util.ArrayList<com.dinuka.planapp.model.UserPlan>>, and MIME media type application/json was not found.
at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:284)
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1510)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409)
at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:128)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:63)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:50)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectRequest(DevAppServerModulesFilter.java:366)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectModuleRequest(DevAppServerModulesFilter.java:349)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doFilter(DevAppServerModulesFilter.java:116)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:98)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:513)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
Caused by: com.sun.jersey.api.MessageException: A message body writer for Java class java.util.Collections$SingletonList, and Java type java.util.List<java.util.ArrayList<com.dinuka.planapp.model.UserPlan>>, and MIME media type application/json was not found.
用户计划Class:
public class UserPlan {
String ID = "";
String Name = "";
String Description = "";
//Getter Setter and Constructors
}
当我调用 API 时，出现上述错误。我做错了什么？
@XmlRootElement
@XmlType(propOrder = {ID, Name, Description})
public class UserPlan {
String ID = "";
String Name = "";
String Description = "";
//Getter Setter and Constructors
}
尝试为 UserPlan 添加 @XmlRootElement @XmlType class
String json = new Gson().toJson(plans);
@GET
@Produces(MediaType.APPLICATION_JSON)
@Path("/getplans/{type}")
public String GetAllPlans(@PathParam("type") String type) {
PlanDAO dao = new PlanDAO();
ArrayList<UserPlan> plans = dao.GetAllPlans_ByType(type);
return new Gson().toJson(plans);
}
此代码有两处错误：
POJO (UserPlan) 不对应任何 built-in provider that jersey support. Typically, a provider(or messagebodyreader/writer) will handle conversion of objects to corresponding MediaType. So, Either create a Provider 你定义的每个自定义 class 或将 class 转换为预处理类型。为您的 POJO 添加 @XmlRootElement 注释使其代表一个 JAXBElement，默认提供程序将为其工作。
要使用通用集合类型，请使用：
ArrayList<UserPlan> plans = dao.GetAllPlans_ByType(type);
GenericEntity entity = new GenericEntity<List<UserPlan>>(plans) {};
return Response.ok(entity).build();
如果您在项目中使用 Maven，请取消注释 pom.xml 文件中的以下行，然后重新启动您的服务器。它将正常工作。
<dependency>
<groupId>org.glassfish.jersey.media</groupId>
<artifactId>jersey-media-moxy</artifactId>
</dependency>
我需要简单地 return 对象的 ArrayList 作为我的 Rest API 响应，但我不断收到此错误：
A message body writer for Java class java.util.Collections$SingletonList and MIME media type application/json was not found.
我的代码：
@Path("/plans")
public class PlanAPI {
@GET
@Produces(MediaType.APPLICATION_JSON)
@Path("/getplans/{type}")
public Response GetAllPlans(@PathParam("type") String type) {
PlanDAO dao = new PlanDAO();
ArrayList<UserPlan> plans = dao.GetAllPlans_ByType(type);
return Response.status(200).entity(plans).build();
}
}
我得到的错误：
com.sun.jersey.spi.container.ContainerResponse logException
SEVERE: Mapped exception to response: 500 (Internal Server Error)
javax.ws.rs.WebApplicationException: com.sun.jersey.api.MessageException: A message body writer for Java class java.util.Collections$SingletonList, and Java type java.util.List<java.util.ArrayList<com.dinuka.planapp.model.UserPlan>>, and MIME media type application/json was not found.
at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:284)
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1510)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409)
at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:128)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:63)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:50)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectRequest(DevAppServerModulesFilter.java:366)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectModuleRequest(DevAppServerModulesFilter.java:349)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doFilter(DevAppServerModulesFilter.java:116)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:98)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:513)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
Caused by: com.sun.jersey.api.MessageException: A message body writer for Java class java.util.Collections$SingletonList, and Java type java.util.List<java.util.ArrayList<com.dinuka.planapp.model.UserPlan>>, and MIME media type application/json was not found.
用户计划Class:
public class UserPlan {
String ID = "";
String Name = "";
String Description = "";
//Getter Setter and Constructors
}
当我调用 API 时，出现上述错误。我做错了什么？
@XmlRootElement
@XmlType(propOrder = {ID, Name, Description})
public class UserPlan {
String ID = "";
String Name = "";
String Description = "";
//Getter Setter and Constructors
}
尝试为 UserPlan 添加 @XmlRootElement @XmlType class
String json = new Gson().toJson(plans);
@GET
@Produces(MediaType.APPLICATION_JSON)
@Path("/getplans/{type}")
public String GetAllPlans(@PathParam("type") String type) {
PlanDAO dao = new PlanDAO();
ArrayList<UserPlan> plans = dao.GetAllPlans_ByType(type);
return new Gson().toJson(plans);
}
此代码有两处错误：
POJO (
UserPlan) 不对应任何 built-in provider that jersey support. Typically, a provider(or messagebodyreader/writer) will handle conversion of objects to corresponding MediaType. So, Either create a Provider 你定义的每个自定义 class 或将 class 转换为预处理类型。为您的 POJO 添加@XmlRootElement注释使其代表一个JAXBElement，默认提供程序将为其工作。要使用通用集合类型，请使用：
ArrayList<UserPlan> plans = dao.GetAllPlans_ByType(type);
GenericEntity entity = new GenericEntity<List<UserPlan>>(plans) {};
return Response.ok(entity).build();
如果您在项目中使用 Maven，请取消注释 pom.xml 文件中的以下行，然后重新启动您的服务器。它将正常工作。
<dependency>
<groupId>org.glassfish.jersey.media</groupId>
<artifactId>jersey-media-moxy</artifactId>
</dependency>