筆者做了一個小的系統輔助功能，可以周期性訪問某個URL、執行某個SQL語句 or 執行某個系統命令。
執行SQL語句和系統命令比較簡單，這裡不再詳述，主要說一下訪問某個URL。
實際上JDK自身已有工具類用於創建HTTP請求，類名是：Java.Net.HttpURLConnection，但考慮到基礎類通常比較粗糙，很多情況要自己考慮和處理，就轉頭去Google了下，發現果然有開源的工具包可以使用，幾個工具包中以HttpClIEnt較為常用，而且是apache的東東，於是決定采用HttpClIEnt。
從apache上down了包commons-httpclient-3.1.jar和commons-codec-1.3.jar兩個包，後者是HttpClIEnt依賴的包。
幫助寫的很好，即便是像我這樣英文很爛，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;
}
本機Tomcat下run一下，工作正常，隨即丟到服務器（Oracle IAS環境）上測試，程序應該出乎意料的報了個錯。
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)
錯誤信息看上去比較低級：NoClassDefFoundError，類沒找到，迅速了檢查了一下本機和服務器上的jar包是否相同，“一模一樣”！這就奇怪了。
檢查本機的開發環境，只添加了這兩個jar，其他的都沒有動過，又檢查服務器的運行環境，一樣沒有變化。於是刪掉本機開發環境下的這兩個jar，問題浮出來了，類中對httpclIEnt的7、8個引用中只有1個提示未找到指定的類，看來Oracle自己的某個包中已經包含某個較低版本的httpclIEnt，jar包沖突的問題是件讓人沮喪的事情，嘗試解決這種問題會所耗費的時間也許是其他方法的N倍，無心戀戰。
其實此處要進行的操作很簡單，就是訪問指定的URL，根據返回的內容檢查是否成功，HttpClIEnt是完整模擬浏覽器，考慮了很多種問題，使用起來反倒是復雜了，決定轉用JDK的基礎類：Java.Net.HttpURLConnection
事情出奇的順利，空間裡找到了之前寫的一個方法，正好解決這個問題，以下是代碼清單：
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 < " + strUrl + " > 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;
}
