JSP页面导入问题。 Class文件放在WEB-INF / classes中的一个包中 [英] JSP Page Import problem. Class file placed in a package inside WEB-INF/classes

问题描述

我有一个Web应用程序crawler_GUI运行，它的buildpath中有另一个java项目jspider。 （我使用eclipse galileo）

GUI使用jspider项目作为其后端。

访问 http：//i45.tinypic。 com / avmszn.jpg 的结构

JSP创建一个jspider对象的实例。首先我没有在WEB-INF / classes文件夹中的类，我纠正了这个错误。现在它似乎工作，没有显示错误，但没有一项任务执行。

这里是代码：

JSP

 <％@ page import =net.javacoding.jspider.ESpider，source.Crawler ％GT; 
<％@ page import =java.net.URL％> 
<％// URL baseURL = new URL（Crawler.SelectedSites.get（0））; 
 URL baseURL =新的URL（http://www.buy.com）; 
 System.out.println（******）; 
 ESpider espider = new ESpider（baseURL）; 
  

打印*。

ESPider.java

  public ESpider（URL baseURL）throws Exception {
 super（baseURL）; 
 System.out.println（test）; 
 
 
} 
  

它不打印测试 。实际上，父进程的构造函数甚至不被调用。同时也不会显示任何错误。

我该如何解决？

解决方案

在Eclipse中，您需要将 jspider crawler_GUI 项目如下：

1. crawler_GUI 属性> Java构建路径>项目>添加 jspider 。


2. crawler_GUI 属性> Java EE模块依赖关系> Tick jspider 。

Don不要手动清除 / WEB-INF / classes 中的任何松散的文件。这是不必要的如果您以正确的方式引用了项目，Eclipse将自动关注此问题。此外，任何松散的JAR文件都应该被放在 / WEB-INF / lib 中。

现在JSP部分故事。由于您在JSP文件而不是真正的Java类中编写了原始的Java代码，所以很难确定根本原因。第一步是检查服务器日志是否存在任何不一致。也可能发生错误版本的 ESpider 类已经加载（缺少sysout）。

扩展HttpServlet 的类，然后使用 ESpider实现 doGet（）方法的东西，最后转发到一个JSP页面来显示结果，在 web.xml 中注册servlet，并通过URL来覆盖它的 url-pattern 在 web.xml 中。 您可以在这里找到很多很好的JSP / Servlet教程。

PS：确保您了解 robots.txt 政策...

I have a Web application crawler_GUI running which has another java project jspider in its buildpath. (I use eclipse galileo)

The GUI uses the jspider project as its backend.

Visit http://i45.tinypic.com/avmszn.jpg for the structure

The JSP creates an instance of the jspider object. First of all I didn't have the classes in the WEB-INF/classes folder and I rectified that error. Now it seems to work, and no errors are shown but none of the tasks are carried out.

Here's the code :

The JSP

<%@ page import = "net.javacoding.jspider.ESpider, source.Crawler"%>
<%@ page import = "java.net.URL" %>
<%//URL baseURL = new URL(Crawler.SelectedSites.get(0));
URL baseURL = new URL("http://www.buy.com");
System.out.println("******");
ESpider espider = new ESpider(baseURL);

The *s get printed.

ESpider.java

public ESpider(URL baseURL) throws Exception {
    super(baseURL);
    System.out.println("test");


}

It doesn't print "test". In fact the parent's constructor isn't even being called. At the same time no errors are displayed either.

How can I fix this?

解决方案

In Eclipse, you need to add the jspider project to the crawler_GUI project as follows:

1. crawler_GUI properties > Java Build Path > Projects > Add jspider.
2. crawler_GUI properties > Java EE Module Dependencies > Tick jspider.

Don't forget to cleanup any loose files in /WEB-INF/classes you've added manually. This is unnecessary. Eclipse will automagically take care about this if you referenced the projects the right way. Also, any loose JAR files are supposed to be just dropped in /WEB-INF/lib.

Now the JSP part of the story. It's hard to pinpoint the root cause since you wrote raw Java code in a JSP file instead of a real Java class. First step would be checking the server logs for any inconsistencies. It may also have happened that the wrong version of the ESpider class has been loaded (which lacks the sysout).

As already hinted, this isn't really the way you're supposed to use JSP. It is to be used to as a template to write HTML/CSS/JS in wherein you can dynamically control the flow with help of taglibs like JSTL and access backend data using EL. Raw Java code belongs in Java classes, not JSP files. In this case you should have used a Servlet class. Just create a class which extends HttpServlet, implement the doGet() method accordingly with the ESpider stuff and finally forward to a JSP page to display the result, register the servlet in web.xml and call it by URL which covers its url-pattern in web.xml. You can find here a lot of good JSP/Servlet tutorials.

P.S: ensure that you understand the robots.txt policy...

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