应用HTTP服务器出现Error 404: NoTargetForURIException问题求助

Let’s walk through the most likely causes for this 404 error and how to fix them, tailored to your setup with CheckServlet and WebSphere:

1. Mismatched or Incorrect Servlet Mapping in web.xml #

This is the most common culprit—WebSphere can’t find a Servlet mapped to the URI you’re requesting.

• Check name consistency: Ensure the <servlet-name> in your <servlet> declaration exactly matches the one in <servlet-mapping>. Even a tiny typo (like lowercase vs uppercase) will break the mapping.
• Verify the url-pattern: Make sure the pattern aligns with the URI you’re using to access the Servlet. For example, if you set <url-pattern>/check-status</url-pattern>, you need to hit http://your-server:port/your-app-context/check-status (replace your-app-context with your application’s context root).
• Example of a correct mapping:

  <servlet>
      <servlet-name>CheckServlet</servlet-name>
      <servlet-class>com.your.package.CheckServlet</servlet-class> <!-- Double-check the full package path -->
  </servlet>
  <servlet-mapping>
      <servlet-name>CheckServlet</servlet-name>
      <url-pattern>/check</url-pattern>
  </servlet-mapping>
  

2. Missing or Misplaced Servlet Class in Deployment #

WebSphere can’t load your CheckServlet if the compiled .class file isn’t in the right location:

• Check your WAR file structure: The CheckServlet.class should live under WEB-INF/classes/com/your/package/ (matching your package structure). If you’re using a JAR for the class, ensure it’s placed in WEB-INF/lib.
• Re-package your WAR to include the class if it’s missing, then re-deploy the application.

3. WebSphere Deployment or Cache Issues #

Sometimes WebSphere fails to load the Servlet correctly even if your config is valid:

• Check the WebSphere Admin Console logs (under Applications > Your App > Logs) for deployment errors. A "class not found" error here means the class isn’t being picked up by the server.
• Clear WebSphere’s temporary files: Delete the contents of [WAS_INSTALL_DIR]/profiles/[YOUR_PROFILE]/temp and [WAS_INSTALL_DIR]/profiles/[YOUR_PROFILE]/work, then restart the application server. This fixes stale cache issues that might prevent the Servlet from registering.

4. Incorrect Request URI #

Double-check the URL you’re using to access the Servlet:

• Don’t forget the application’s context root. If your app is deployed with context root my-app, the full URL should be http://server:port/my-app/check (matching your url-pattern).
• Case matters in most WebSphere setups—for example, /Check won’t match a pattern set to /check.

5. Redundant Servlet Interface Implementation (Minor Cleanup) #

While this won’t directly cause a 404, your CheckServlet code has a redundant implements Servlet—since HttpServlet already implements the Servlet interface. You can safely remove that to clean up your code:

public class CheckServlet extends HttpServlet { // Remove "implements Servlet"
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try (PrintWriter out = response.getWriter()) {
            response.setContentType("text/html");
            out.print("<html><body>");
            out.printf("Application '%s' is active", getServletContext().getContextName());
            out.print("</body></html>");
        }
    }
}

内容的提问来源于stack exchange，提问作者Harsha