最近几年来，地理信息系统无论是在理论上还是应用上都处在一个飞速发展的阶段。 GIS被应用于多个领域的建模和决策支持，如城市管理、区划、环境整治等等，地理信息成为信息时代重要的组成部分之一； “数字地球”概念的提出，更进一步推动了作为其技术支撑的GIS的发展。 与此同时，一些学者致力于相关的理论研究，如空间感知、空间数据误差、空间关系的形式化等等。 这恰好说明了地理信息系统作为应用技术和学科的两个方面，并且这两个方面构成了相互促进的发展过程。
Testing / debugging Servlet is always a difficult point in the process of development and use. Servlet often involves a large number of client / server interactions, and errors can occur but are difficult to reproduce.
Here are some tips and suggestions to help you debug. Because the System object is part of the core Java object, it can be used anywhere without installing any additional classes. This includes Servlet, JSP, RMI, EJB’s, plain Beans and classes, as well as stand-alone applications. Instead of stopping at a breakpoint, write to the The following is to use the All messages generated through the above syntax will be logged in the Web server log file. It is a very good idea to use appropriate logging methods to record all debug, warning, and error messages, and it is recommended to use log4J to record all the messages. Servlet API also provides a simple way to output information, using the These log files do indicate the frequency of new errors or problems. Because of this, it is recommended that exceptions that do not normally occur You can debug Servlet using the jdb command to debug applet or an application. To debug a Servlet, we can debug Most debuggers automatically hide how to debug Set the classpath classpath of your debugger so that it can find Set the classpath of your debugger You don’t usually want If you have set the correct classpath Comments in your code help debug in a variety of ways. Comments can be used in many other ways of debugging the process. The Servlet uses Java comments and single-line comments (/ /…), and multiline comments (/) * …* /) can be used to temporarily remove part ofthe Java code. If the bug disappears, take a closer look at the code you just commented out and find out what the problem is. Sometimes it is useful to look at the original HTTP request and response when a Servlet is not as expected. If you are familiar with the HTTP structure, you can read the request and response to see what these headers are. Here are some tips for Servlet debugging: Attention please, Requires the browser to display the original content of the page it displays. This helps to identify format problems. It is usually an option under the View menu. Ensure that the browser has not cached the output of the previous request byforcing a complete reload of the page. In Netscape Navigator, use Shift-Reload, and in Internet Explorer, use Shift-Refresh. Please confirm servlet’s 2.22.1.
System.out.println() ¶ System.out.println() is used as a tag to test whether a particular pieceof code is executed. We can also print out the value of the variable. In addition: System.out it does not interfere with the normal execution of the application, which makes it particularly valuable when timing is critical. System.out.println() syntax:System.out.println("Debugging message");
2.22.2. Message log ¶
log() method, as follows:// Import necessary Java libraries import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class ContextLog extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, java.io.IOException { String par = request.getParameter("par1"); // Calling two ServletContext. log methods ServletContext context = getServletContext( ); if (par == null || par.equals("")) // Record version through Throwable parameter context.log("No message received:", new IllegalStateException("Missing parameter")); else context.log("Here is the visitor's message: " + par); response.setContentType("text/html;charset=UTF-8"); java.io.PrintWriter out = response.getWriter( ); String title = "Context Log"; String docType = " \n"; out.println(docType + "\n" + "
\"center\">" + title + "\n" + "
\"center\">Messages sent\n" + ""); } //doGet }
ServletContext log its text message to the log file of the Servlet container. For Tomcat, these logs can be found in the catch used in the clause log() function. 2.22.3. Using the JDB Debugger ¶
sun.servlet.http.HttpServer and think of it as HttpServer execute Servlet to respond to the HTTP request on the browser side. This is very similar to debugging applet Mini Program. Unlike debugging applet, the actual program being debugged is sun.applet.AppletViewer . applet the details. Similarly, for servlet, you must do the following for the debugger:
sun.servlet.http.Http-Server and related classes. classpath so that it can find your servlet and supported classes, usually in the server_root/servlets and server_root/classes . server_root/servlets in your classpath ,because it disables the reload of servlet. But this inclusion rule is very useful for debugging. It allows your debugger to set breakpoints in the Servlet before the custom Servlet loader in HttpServer loads the Servlet. classpath can start debugging``sun.servlet.http.HttpServer`` . You can set a breakpoint in the Servlet code you want to debug and then make a request to HttpServer using the givenServlet ( http://localhost:8080/servlet/ServletToDebug ) through the Web browser. You will see that the execution of the program stops at the breakpoint. 2.22.4. Working with comments ¶
2.22.5. Client and server header information ¶
2.22.6. Important debugging skills ¶
server_root/classes will not be overloaded, and server_root/servlets it might. init() method to accept a ServletConfig parameter and call the super.init(config) .