我正在寻找一种方法，如何在应用程序＃2的资源中调用应用程序＃1的GET资源。因此我尝试使用Jersey-client API。
两个应用程序都在Apache Tomcat / 8.0.23（localhost：8099）上运行。对于这两者，我使用Jersey 2.19作为JAX-RS实现来创建RESTful资源。
应用程序＃1（记录应用程序）：
@Path("records")
public class RecordResource {
@GET
@Path("test")
@Produces(MediaType.TEXT_PLAIN)
public String getTest() {
return "Hello World :-)";
}
}
申请＃2（claim-app）：
@Path("claims")
public class ClaimResource {
@POST
public void postTest() {
Client client = ClientBuilder.newClient();
WebTarget target = client.target("http://localhost:8099/record-app/rest/records/test");
Invocation.Builder invocationBuilder = target.request(MediaType.TEXT_PLAIN);
Response responseRecordApp = invocationBuilder.get();
System.out.println(responseRecordApp.getStatus());
System.out.println(responseRecordApp.readEntity(String.class));
}
在声明资源上发布POST后，我得到了这个NoClassDefFoundError：ThreadPoolExecutorProvider
30-Jul-2015 09:56:21.476 SEVERE [http-apr-8099-exec-7] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [org.claims.App] in context with path [/claim-app] threw exception [org.glassfish.jersey.server.ContainerException: java.lang.NoClassDefFoundError: org/glassfish/jersey/spi/ThreadPoolExecutorProvider] with root cause
java.lang.ClassNotFoundException: org.glassfish.jersey.spi.ThreadPoolExecutorProvider
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1305)
...
对我而言，这看起来像Tomcat缺少一些库。我想知道这是怎么回事，因为我正在使用Maven依赖（并且我没有将它们标记为提供）。
claim-app的pom.xml：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-resource"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>claim-app</artifactId>
<version>1.0</version>
<packaging>war</packaging>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<configuration>
<outputDirectory>C:\apache-tomcat-8.0.23\webapps\</outputDirectory>
</configuration>
</plugin>
</plugins>
<finalName>${artifactId}</finalName>
</build>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.glassfish.jersey</groupId>
<artifactId>jersey-bom</artifactId>
<version>2.17</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>org.glassfish.jersey.containers</groupId>
<artifactId>jersey-container-servlet</artifactId>
<version>2.19</version>
</dependency>
<dependency>
<groupId>org.glassfish.jersey.core</groupId>
<artifactId>jersey-client</artifactId>
<version>2.19</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
</dependency>
</dependencies>
</project>
无论如何，我将缺少的库（ThreadPoolExecutorProvider所在的位置）添加到tomcat / lib文件夹中。之后我得到了更多的NoClassDefFoundErrors，所以我最终得到了这个罐子列表：
jersey-apache-connector-2.19
jaxrs-ri-2.19
jersey-container-jdk-http-2.19
jersey-container-simple-http-2.19
jersey-guava-2.19
jersey-server-2.19
jersey-common-2.19
jersey-media-jaxb-2.19
jersey-container-servlet-core-2.19
hk2-api-2.4.0-b25
hk2-locator-2.4.0-b25
hk2-utils-2.4.0-b25
javax.inject-2.4.0-b25
jersey-client-2.19
jersey-container-servlet-2.19
在我摆脱NoClassDefFoundErrors后，发生以下异常：
type Exception report
message org.glassfish.jersey.server.ContainerException: java.lang.LinkageError: loader constraint violation: loader (instance of java/net/URLClassLoader) previously initiated loading for a different type with name "org/glassfish/hk2/api/ServiceLocator"
description The server encountered an internal error that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: org.glassfish.jersey.server.ContainerException: java.lang.LinkageError: loader constraint violation: loader (instance of java/net/URLClassLoader) previously initiated loading for a different type with name "org/glassfish/hk2/api/ServiceLocator"
org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:421)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:386)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:335)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:222)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause
org.glassfish.jersey.server.ContainerException: java.lang.LinkageError: loader constraint violation: loader (instance of java/net/URLClassLoader) previously initiated loading for a different type with name "org/glassfish/hk2/api/ServiceLocator"
org.glassfish.jersey.servlet.internal.ResponseWriter.rethrow(ResponseWriter.java:256)
org.glassfish.jersey.servlet.internal.ResponseWriter.failure(ResponseWriter.java:238)
org.glassfish.jersey.server.ServerRuntime$Responder.process(ServerRuntime.java:483)
org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:313)
org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
org.glassfish.jersey.internal.Errors.process(Errors.java:315)
org.glassfish.jersey.internal.Errors.process(Errors.java:297)
org.glassfish.jersey.internal.Errors.process(Errors.java:267)
org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:288)
org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1110)
org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:401)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:386)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:335)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:222)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause
java.lang.LinkageError: loader constraint violation: loader (instance of java/net/URLClassLoader) previously initiated loading for a different type with name "org/glassfish/hk2/api/ServiceLocator"
java.lang.ClassLoader.defineClass1(Native Method)
java.lang.ClassLoader.defineClass(Unknown Source)
java.security.SecureClassLoader.defineClass(Unknown Source)
java.net.URLClassLoader.defineClass(Unknown Source)
java.net.URLClassLoader.access$100(Unknown Source)
java.net.URLClassLoader$1.run(Unknown Source)
java.net.URLClassLoader$1.run(Unknown Source)
java.security.AccessController.doPrivileged(Native Method)
java.net.URLClassLoader.findClass(Unknown Source)
java.lang.ClassLoader.loadClass(Unknown Source)
java.lang.ClassLoader.loadClass(Unknown Source)
org.glassfish.jersey.internal.inject.Providers.getServiceHandles(Providers.java:354)
org.glassfish.jersey.internal.inject.Providers.getCustomProviders(Providers.java:201)
org.glassfish.jersey.process.internal.ExecutorProviders.getQualifierToProviderMap(ExecutorProviders.java:191)
org.glassfish.jersey.process.internal.ExecutorProviders.createInjectionBindings(ExecutorProviders.java:103)
org.glassfish.jersey.client.ClientConfig$State.initRuntime(ClientConfig.java:415)
org.glassfish.jersey.client.ClientConfig$State.access$000(ClientConfig.java:88)
org.glassfish.jersey.client.ClientConfig$State$3.get(ClientConfig.java:120)
org.glassfish.jersey.client.ClientConfig$State$3.get(ClientConfig.java:117)
org.glassfish.jersey.internal.util.collection.Values$LazyValueImpl.get(Values.java:340)
org.glassfish.jersey.client.ClientConfig.getRuntime(ClientConfig.java:726)
org.glassfish.jersey.client.ClientRequest.getConfiguration(ClientRequest.java:285)
org.glassfish.jersey.client.JerseyInvocation.validateHttpMethodAndEntity(JerseyInvocation.java:126)
org.glassfish.jersey.client.JerseyInvocation.<init>(JerseyInvocation.java:98)
org.glassfish.jersey.client.JerseyInvocation.<init>(JerseyInvocation.java:91)
org.glassfish.jersey.client.JerseyInvocation$Builder.method(JerseyInvocation.java:402)
org.glassfish.jersey.client.JerseyInvocation$Builder.get(JerseyInvocation.java:302)
org.claims.controller.ClaimResource.postTest(ClaimResource.java:39)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
java.lang.reflect.Method.invoke(Unknown Source)
org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:164)
org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:181)
org.glassfish.jersey.server.model.internal.VoidVoidDispatcherProvider$VoidToVoidDispatcher.doDispatch(VoidVoidDispatcherProvider.java:80)
org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:101)
org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:389)
org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:347)
org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:102)
org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:305)
org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
org.glassfish.jersey.internal.Errors.process(Errors.java:315)
org.glassfish.jersey.internal.Errors.process(Errors.java:297)
org.glassfish.jersey.internal.Errors.process(Errors.java:267)
org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:288)
org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1110)
org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:401)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:386)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:335)
org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:222)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
note The full stack trace of the root cause is available in the Apache Tomcat/8.0.23 logs.
Apache Tomcat/8.0.23
如果我在一个没有在tomcat上运行的简单Java类中使用相同的postTest（）代码，我不会得到异常并且结果是正确的：
200
Hello World :-)
所以我认为问题必须在Tomcat服务器的某个地方。对我来说，看起来我在应用程序＃2中使用的Jersey客户端以某种方式逃脱了servlet容器。这就是为什么我可能得到了所有这些NoClassDefErrors。但我不确定......
有人知道这里出了什么问题吗？ 或者是否有另一种方法可以从另一个REST资源在REST资源上发出HTTP请求？
解： 解决方案是删除像@peeskillet建议的jersey-client依赖。