当我在 Tomcat 7.0 上运行我的 servlet 时，我不断收到这个错误。看来我找不到问题出在哪里。代码对我来说看起来不错。
这是我的 Servlet。
package com.servlets;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/querymvservlet")
public class QueryServletMv extends HttpServlet {
private static final long serialVersionUID = 1L;
public QueryServletMv() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// Set the MIME type for the response message
response.setContentType("text/html");
//Get a output writer to write the response into the network
PrintWriter out = response.getWriter();
Connection conn = null;
Statement stmt = null;
try {
Class.forName("com.mysql.jdbc.Driver");
// STEP 1: Create a database "Connection" object
// For MySQL
conn = DriverManager.getConnection("jdbc:mysql://localhost /ebookshop", "root", "");
// STEP 2: Create a "Statement" object inside the "Connection"
stmt = conn.createStatement();
// STEP 3: Execute a SQL SELECT query
String[] authors = request.getParameterValues("author");
if(authors == null){
out.println("<h2>Please go back and select an author</>");
return;
}
String sql = "SELECT * FROM books WHERE author IN (";
sql +="'" + authors[0] + "'"; // First author
for (int i = 1; i < authors.length; i++ ){
sql += ", '" + authors[i] + "'";
}
sql += ") AND qty > 0 ORDER BY author ASC, title ASC";
// Print an HTML page as output of query
out.println("<html><head><title></title></head><body>");
out.println("<h2>Thank you for your query. </h2>");
out.println("<p>Your query is: " + sql + "</p>");
// Send the query to the server
ResultSet rs = stmt.executeQuery(sql);
// STEP 4: Process the query result
int count = 0;
while (rs.next()) {
// Print a paragraph <p>....</p> for each row
out.println("<p>"+ rs.getString("author")
+ ", " + rs.getString("title")
+ ", $" + rs.getDouble("price") + "<p>");
++count;
}
out.println("<p>==========" + count + " records found ======</p>");
out.println("</body></html>");
} catch (SQLException ex) {
ex.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} finally {
out.close();
try {
// STEP 5: Close the Statement and Connection
if(stmt != null) stmt.close();
if(conn != null) conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
这是 html 页面:
<html>
<head>
<title>Yet another e-Bookshop MV</title>
</head>
<body>
<h2>Yet Another e-Bookshop MV</h2>
<form method="get" action="querymvservlet">
Choose an author: <br /><br />
<input type="checkbox" name="author" value="Tan Ah Teck" />Ah Teck
<input type="checkbox" name="author" value="Mohammad Ali" /> Ali
<input type="checkbox" name="author" value="Kumar" />Kumar
<input type="checkbox" name="author" value="Kevin Jones" />Kevin
<input type="submit" value="Search" />
</form>
</body>
</html>
Web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com /xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<servlet>
<servlet-name>querybookmv</servlet-name>
<servlet-class>com.servlets.QueryServletMv</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>querybookmv</servlet-name>
<url-pattern>/querymvservlet</url-pattern>
</servlet-mapping>
</web-app>
我得到了 ClassNotFoundException，但我使用了正确的包名。 这是堆栈跟踪
type Exception report
message Error instantiating servlet class com.servlets.QueryServletMv
description The server encountered an internal error that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: Error instantiating servlet class com.servlets.QueryServletMv
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1074)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:745)
root cause
java.lang.ClassNotFoundException: com.servlets.QueryServletMv
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1074)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:745)
最佳答案
404 或 Not Found 错误消息是一个 HTTP 标准响应代码，表示客户端能够与给定服务器通信，但服务器找不到所请求的内容。
当用户试图访问损坏或失效的链接时，网站托管服务器通常会生成“404 Not Found”网页；因此，404 错误是用户可以在网络上找到的最容易识别的错误之一。
首先检查您的服务器是否列出了您的端口号:
使用localhost://portnumber
关于java.lang.ClassNotFoundException : com. servlets.QueryServletMv 异常，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30934641/