笔者做了一个小的体系辅佐功用，能够周期性拜访某个URL、履行某个SQL句子 or 履行某个体系指令。

履行SQL句子和体系指令比较简单，这儿不再胪陈，主要说一下拜访某个URL。

实际上JDK本身已有东西类用于创立HTTP恳求，类名是：java.net.HttpURLConnection，但考虑到根底类一般比较粗糙，许多状况要自己考虑和处理，就回头去Google了下，发现果然有开源的东西包能够运用，几个东西包中以HttpClient较为常用，并且是apache的东东，所以决议选用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依靠的包。

协助写的很好，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，作业正常，随即丢到服务器（Oracle IAS环境）上测验，程序应该出人意料的报了个错。

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)

错误信息看上去比较初级：NoClassDefFoundError，类没找到，敏捷了查看了一下本机和服务器上的jar包是否相同，“如出一辙”！这就奇怪了。

查看本机的开发环境，只添加了这两个jar，其他的都没有动过，又查看服务器的运转环境，相同没有改变。所以删掉本机开发环境下的这两个jar，问题浮出来了，类中对httpclient的7、8个引证中只要1个提示未找到指定的类，看来Oracle自己的某个包中现已包括某个较低版别的httpclient，jar包抵触的问题是件让人懊丧的工作，测验处理这种问题会所消耗的时刻也许是其他办法的N倍，无心恋战。

其实此处要进行的操作很简单，便是拜访指定的URL，依据回来的内容查看是否成功，HttpClient是完好模仿浏览器，考虑了许多种问题，运用起来反倒是杂乱了，决议转用JDK的根底类：java.net.HttpURLConnection

工作出奇的顺畅，空间里找到了之前写的一个办法，正好处理这个问题，以下是代码清单：

 private boolean visitURL(String strUrl, String successFlag) {

 boolean rs = false;
 HttpURLConnection jconn = null;
 ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
 try {
 URL url = new URL(strUrl);
 jconn = (HttpURLConnection) url.openConnection();
 jconn.setDoOutput(true);
 jconn.setDoInput(true);
 jconn.connect();

 InputStream in = jconn.getInputStream();
 byte[] buf = new byte[4096];
 int bytesRead;
 while ((bytesRead = in.read(buf)) != -1) {
 byteArrayOutputStream.write(buf, 0, bytesRead);
 }
 String strRead = new String(byteArrayOutputStream.toByteArray());

 logger.debug(strRead);

 strRead = StringUtil.NVL(strRead);

 if(strRead.indexOf(successFlag) != -1) {
 logger.info("Visit URL  success !");
 rs = true;
 }

 } catch (MalformedURLException e) {
 e.printStackTrace();
 } catch (IOException e) {
 e.printStackTrace();
 } finally {
 jconn.disconnect();
 try {
 byteArrayOutputStream.close();
 } catch (IOException e) {
 e.printStackTrace();
 }
 }

 return rs;
 }

【修改引荐】

1. 实例解说Oracle 9i数据坏块的处理
2. Oracle 11g中完成自我调整功用
3. Oracle数据库规划提高功能的五条规律