java.lang.NoClassDefFoundError: org/apache/http/client/HttpClient [英] java.lang.NoClassDefFoundError: org/apache/http/client/HttpClient
问题描述
我正在尝试从 GWT servlet 发出获取请求，以从 Web 服务获取 JSON 响应.以下是我的 servlet 中的代码:
I am trying to make a get request from the GWT servlet to get JSON response from a web service. Following is the code in my servlet :
public String getQueData() throws IllegalArgumentException {
String message = null;
try {
HttpClient httpclient = new DefaultHttpClient();
JSONParser parser = new JSONParser();
String url = "working - url";
HttpResponse response = null;
response = httpclient.execute(new HttpGet(url));
JSONObject json_data = null;
json_data = (JSONObject)parser.parse(EntityUtils.toString(response.getEntity()));
JSONArray results = (JSONArray)json_data.get("result");
for (Object queid : results) {
message = message.concat((String) ((JSONObject)queid).get("id"));
message = message.concat(" ");
message = message.concat((String) ((JSONObject)queid).get("owner"));
message = message.concat("
");
}
} catch (Exception e) {
message = e.toString();
}
return message;
}
尝试从 GWT servlet 发出获取请求时出现以下异常.
Getting the following exception on trying to make get request from a GWT servlet.
java.lang.NoClassDefFoundError: org/apache/http/client/HttpClient
at java.lang.Class.getDeclaredConstructors0(Native Method)
at java.lang.Class.privateGetDeclaredConstructors(Class.java:2389)
at java.lang.Class.getConstructor0(Class.java:2699)
at java.lang.Class.newInstance0(Class.java:326)
at java.lang.Class.newInstance(Class.java:308)
at org.mortbay.jetty.servlet.Holder.newInstance(Holder.java:153)
at org.mortbay.jetty.servlet.ServletHolder.initServlet(ServletHolder.java:428)
at org.mortbay.jetty.servlet.ServletHolder.getServlet(ServletHolder.java:339)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:35)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:60)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:122)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
at org.mortbay.jetty.servlet.ServletHandler$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:78)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:362)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
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: java.lang.ClassNotFoundException: org.apache.http.client.HttpClient
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at com.google.appengine.tools.development.IsolatedAppClassLoader.loadClass(IsolatedAppClassLoader.java:176)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
此异常的可能原因是什么?如何删除?
What could be the possible cause of this exception? How it could be removed?
我在 ubuntu 10.04 上使用 jdk1.6.0_30.
I am using jdk1.6.0_30 on ubuntu 10.04.
推荐答案
此异常的可能原因是什么?
What could be the possible cause of this exception?
您的类路径中可能没有合适的 Jar.
You may not have appropriate Jar in your class path.
如何删除?
通过将 HTTPClient jar 放在您的类路径中.如果它是一个 web 应用程序，将 Jar 复制到 WEB-INF/lib 如果它是独立的，请确保您在类路径中有此 jar 或使用 -cp 选项显式设置
By putting HTTPClient jar in your class path. If it's a webapp, copy Jar into WEB-INF/lib if it's standalone, make sure you have this jar in class path or explicitly set using -cp option
正如 doc 所说，
如果 Java 虚拟机或 ClassLoader 实例尝试在类的定义中加载(作为正常方法调用的一部分或作为使用 new 表达式创建新实例的一部分)并且类的定义无法加载，则抛出被发现.
Thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found.
在编译当前执行的类时，搜索到的类定义存在，但找不到该定义.
如果您使用的是 Maven/Gradle(请参阅下面的答案)或 SBT 等依赖项管理，请使用它为您带来 httpclient jar.
If you are using a dependency management like Maven/Gradle (see the answer below) or SBT please use it to bring the httpclient jar for you.
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