Servlet引用其他项目导致Tomcat服务器无法启动求助

Hey there! Let's break down the most common pitfalls and fixes for getting your two Java projects working smoothly together—since you mentioned something goes wrong once the login flow kicks off, I’ll cover the issues I’ve run into most often with this exact setup:

1. Classpath/Deployment Failures (The #1 Culprit!) #

If your Servlet throws a ClassNotFoundException when trying to use classes from the Controllers project, it means the web app can’t find the dependency at runtime:

• For Eclipse Dynamic Web Projects:
  • First, link the Controllers project to your web project: Right-click web project → Build Path → Add Projects → Select your Controllers project and confirm.
  • Then ensure it gets deployed to the server: Right-click web project → Properties → Deployment Assembly → Add → Project → Pick Controllers and add it. Without this step, the server won’t include the Controllers classes when launching the app.
• For Maven Projects:
  • Package your Controllers project as a JAR and install it to your local repo:

    mvn clean install
    

  • Add this dependency to your web project’s pom.xml:

    <dependency>
        <groupId>your.group.id</groupId>
        <artifactId>controllers-project</artifactId>
        <version>1.0.0</version>
    </dependency>
    

2. Database Connection Errors #

If the Servlet can access Controllers classes but fails to connect to the DB:

• Double-check the DB config in your Controllers classes: Ensure the URL, username, password, and driver class are correct. For MySQL, use com.mysql.cj.jdbc.Driver (not the old com.mysql.jdbc.Driver) and add a timezone parameter to the URL: jdbc:mysql://localhost:3306/your_db?serverTimezone=UTC.
• Make sure your web project’s WEB-INF/lib folder includes the database driver JAR (e.g., mysql-connector-java.jar). Even if the Controllers project references the driver, the web app needs its own copy to run on the server.

3. Login Redirect/Forward Failures #

If password validation passes but you don’t land on the WelcomePage:

• Verify your Servlet’s redirect/forward code:
  • For a redirect (browser URL updates):

    response.sendRedirect("WelcomePage.jsp");
    

    Ensure the path matches your JSP’s location—if it’s in a subfolder like pages/, use "/pages/WelcomePage.jsp".
  • For a request forward (URL stays the same):

    request.getRequestDispatcher("WelcomePage.jsp").forward(request, response);
    

• Check your LoginPage.jsp form’s action attribute: If your Servlet is mapped to /LoginServlet, the form should have <form action="LoginServlet" method="post">.

4. Session Data Loss on WelcomePage #

If the WelcomePage doesn’t display the logged-in user’s info:

• After successful validation, store the user data in the session:

  request.getSession().setAttribute("loggedInUser", username);
  

• In WelcomePage.jsp, make sure EL expressions are enabled (add this at the top if needed):

  <%@ page isELIgnored="false" %>
  

  Then access the session data with ${loggedInUser}.

内容的提问来源于stack exchange，提问作者Harlizonian