如何在Eclipse JEE中调用Servlet并在JSP显示学生数据表？

Let's work through this issue step by step—here are the most common culprits and fixes based on your code:

1. Missing JSTL Tag Library Declaration #

The <c:forEach> and <c:out> tags won't work unless you've imported the JSTL core library at the top of your StudentList.jsp. This is a super common oversight that causes the loop to not execute at all (resulting in only table headers showing).

Add this line to the very top of your JSP file:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

2. Mismatched Getter Methods in the Student Class #

EL expressions like ${studentObject.lastName} rely on standard JavaBean getter methods to access properties. If your Student class doesn't have correctly named getters, the EL engine can't retrieve the values, leading to empty table cells.

Make sure your Student class includes these exact getter methods (case matters!):

public class Student {
    private int id;
    private String firstName;
    private String lastName;
    private String street;
    private String postCode;
    private String postOffice;

    // Constructor (matches your DAO's usage)
    public Student(int id, String firstName, String lastName, String street, String postCode, String postOffice) {
        this.id = id;
        this.firstName = firstName;
        this.lastName = lastName;
        this.street = street;
        this.postCode = postCode;
        this.postOffice = postOffice;
    }

    // Required getters for EL access
    public int getId() { return id; }
    public String getFirstName() { return firstName; }
    public String getLastName() { return lastName; }
    public String getStreet() { return street; }
    public String getPostCode() { return postCode; }
    public String getPostOffice() { return postOffice; }
}

For example, if your getter was named getLastname() (lowercase n instead of N), ${studentObject.lastName} would return null.

3. Verify DAO is Actually Retrieving Data #

Even if your database connection works, your DAO might not be fetching any rows. Add a debug print statement in your Servlet to confirm the size of studentList:

studentList = studentDAO.getAllStudents();
// Add this line to check if data is being fetched
System.out.println("Number of students retrieved: " + studentList.size());
request.setAttribute("studentList", studentList);

If the output is 0, check:

• Your SQL table name: Is it Student (case-sensitive on some databases like MySQL/Linux)?
• Database data: Does the Student table actually have rows?
• Column names: Ensure the column names in your SQL (id, firstname, etc.) exactly match what's in your database.

4. Ensure EL Expressions Are Enabled #

If your project uses an older version of the Servlet API (2.3 or earlier), EL expressions are disabled by default. Add this to the top of your JSP to enable them:

<%@ page isELIgnored="false" %>

Most modern projects use Servlet 2.4+ where EL is enabled by default, but it's worth checking if you're working with legacy code.

5. Confirm JSP Table Structure is Complete #

Make sure your <c:forEach> loop is wrapped inside a valid <table> structure with proper headers. Your full JSP table code should look like this:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ page isELIgnored="false" %>

<table border="1">
    <thead>
        <tr>
            <th>ID</th>
            <th>Last Name</th>
            <th>First Name</th>
            <th>Street Address</th>
            <th>Post Code</th>
            <th>Post Office</th>
        </tr>
    </thead>
    <tbody>
        <c:forEach items="${studentList}" var="studentObject">
            <tr>
                <td><c:out value="${studentObject.id}" /></td>
                <td><c:out value="${studentObject.lastName}" /></td>
                <td><c:out value="${studentObject.firstName}" /></td>
                <td><c:out value="${studentObject.street}" /></td>
                <td><c:out value="${studentObject.postCode}" /></td>
                <td><c:out value="${studentObject.postOffice}" /></td>
            </tr>
        </c:forEach>
    </tbody>
</table>

Start with the first two checks (JSTL import and getter methods)—those are the most likely fixes for your issue!

内容的提问来源于stack exchange，提问作者ITGirl