笔者做了一个小的系统辅助功能，可以周期性访问某个URL、执行某个SQL语句or 执行某个系统命令 。
执行SQL语句和系统命令比较简单，这里不再详述，主要说一下访问某个URL。
实际上JDK自身已有工具类用于创建HTTP请求，类名是：java.net.HttpURLConnection，但考虑到基础类通常比 较粗糙，很多情况要自己考虑和处理，就转头去Google了下，发现果然有开源的工具包可以使用，几个工具包中以HttpClient较为常用，而且是apache的东东，于是决定采用HttpClient。
从apache上 down了包commons-httpclient-3.1.jar和commons-codec-1.3.jar两个包，后者是HttpClient依赖的包。
帮助写的很好，即便是像我这样英文很烂，也能很快上手。
public boolean visitURL(String url) {
// Commons HttpClient 3.1
HttpClient client = new HttpClient();
HttpMethod method = new GetMethod(url);
// Provide custom retry handler is necessary
method.getParams().setParameter(HttpMethodParams.RETRY_HANDLER, new DefaultHttpMethodRetryHandler(3, false));
boolean rs = false;
try {
// Execute the method.
int statusCode = client.executeMethod(method);
if (statusCode != HttpStatus.SC_OK) {
logger.error("Method failed: " + method.getStatusLine());
}
else {
rs = true;
}
} catch (HttpException e) {
logger.error("Fatal protocol violation: " + e.getMessage());
} catch (IOException e) {
logger.error("Fatal transport error: " + e.getMessage());
} finally {
// Release the connection.
method.releaseConnection();
}
return rs;
}
本机Tomcat下run一下，工作正常，随即丢到服务器（Oracle IAS环境）上测试，程序 应该出乎意料的报了个错。
09/03/16 19:03:43 java.lang.NoClassDefFoundError
09/03/16 19:03:43 at org.apache.commons.httpclient.HttpMethodBase.writeRequestLine (HttpMethodBase.java:2015)
09/03/16 19:03:43 at org.apache.commons.httpclient.HttpMethodBase.writeRequest (HttpMethodBase.java:1864)
09/03/16 19:03:43 at org.apache.commons.httpclient.HttpMethodBase.execute (HttpMethodBase.java:975)
09/03/16 19:03:43 at org.apache.commons.httpclient.HttpMethodDirector.executeWithRetry (HttpMethodDirector.java:368)
09/03/16 19:03:43 at org.apache.commons.httpclient.HttpMethodDirector.executeMethod (HttpMethodDirector.java:164)
09/03/16 19:03:43 at org.apache.commons.httpclient.HttpClient.executeMethod (HttpClient.java:437)
09/03/16 19:03:43 at org.apache.commons.httpclient.HttpClient.executeMethod (HttpClient.java:324)
09/03/16 19:03:43 at com.zbht.util.TimerTaskManager.runURLTask (TimerTaskManager.java:237)
09/03/16 19:03:43 at _system._timer__task._test._jspService(_test.java:182)
09/03/16 19:03:43 at com.orionserver.http.OrionHttpJspPage.service (OrionHttpJspPage.java:59)
09/03/16 19:03:43 at oracle.jsp.runtimev2.JspPageTable.service(JspPageTable.java:462)
09/03/16 19:03:43 at oracle.jsp.runtimev2.JspServlet.internalService (JspServlet.java:594)
09/03/16 19:03:43 at oracle.jsp.runtimev2.JspServlet.service(JspServlet.java:518)
09/03/16 19:03:43 at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
09/03/16 19:03:43 at com.evermind.server.http.ServletRequestDispatcher.invoke (ServletRequestDispatcher.java:713)
09/03/16 19:03:43 at com.evermind.server.http.ServletRequestDispatcher.forwardInternal (ServletRequestDispatcher.java:370)
09/03/16 19:03:43 at com.evermind.server.http.HttpRequestHandler.doProcessRequest (HttpRequestHandler.java:871)
09/03/16 19:03:43 at com.evermind.server.http.HttpRequestHandler.processRequest (HttpRequestHandler.java:453)
09/03/16 19:03:43 at com.evermind.server.http.AJPRequestHandler.run (AJPRequestHandler.java:302)
09/03/16 19:03:43 at com.evermind.server.http.AJPRequestHandler.run (AJPRequestHandler.java:190)
09/03/16 19:03:43 at oracle.oc4j.network.ServerSocketReadHandler$SafeRunnable.run (ServerSocketReadHandler.java:260)
09/03/16 19:03:43 at com.evermind.util.ReleasableResourcePooledExecutor$MyWorker.run (ReleasableResourcePooledExecutor.java:303)
09/03/16 19:03:43 at java.lang.Thread.run(Thread.java:595)