将表从 Servlet (java) 更新到 MySQL

Question

protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    connection.connect.connection();
    response.setContentType("text/html");
    Integer rating;
    String feedback, sql;
    PreparedStatement insert;
    RequestDispatcher reqdisp;
    try {
        connection.connect.con.setAutoCommit(false);

        rating = Integer.parseInt(request.getParameter("rating"));
        feedback = request.getParameter("feedback").trim();

        sql = "update Message set rating=?, feedback=? WHERE mid=LAST_INSERT_ID()";
        insert = connection.connect.con.prepareStatement(sql);
        insert.setObject(1, rating);
        insert.setObject(2, feedback);
        insert.executeUpdate();
        JOptionPane.showMessageDialog(null, "Successfully inserted");
        connection.connect.con.commit();
        connection.connect.con.close();                                          
} catch (Exception e) {
   System.out.println(e);
        if (connection.connect.con != null) {
            try {
                connection.connect.con.rollback();
                connection.connect.con.close();
            } catch (SQLException ex) {
                JOptionPane.showMessageDialog(null, "Error");
            }
        }
    }
    reqdisp = getServletContext().getRequestDispatcher("/thankYou.jsp");
    reqdisp.forward(request, response);

}

此代码不会产生任何错误，但表永远不会更新。有人可以帮我找出我的 MySQL 查询中的问题吗？谢谢！

    Jun 20, 2017 12:29:09 PM org.apache.tomcat.util.digester.SetPropertiesRule begin
WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:Messages' did not find a matching property.
Jun 20, 2017 12:29:09 PM org.apache.tomcat.util.digester.SetPropertiesRule begin
WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:TestingJSP' did not find a matching property.
Jun 20, 2017 12:29:09 PM org.apache.tomcat.util.digester.SetPropertiesRule begin
WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:JQueryAjaxDemo' did not find a matching property.
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server version:        Apache Tomcat/9.0.0.M21
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server built:          May 4 2017 22:42:36 UTC
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server number:         9.0.0.0
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: OS Name:               Mac OS X
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: OS Version:            10.12.5
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Architecture:          x86_64
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Java Home:             /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: JVM Version:           1.8.0_131-b11
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: JVM Vendor:            Oracle Corporation
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: CATALINA_BASE:         /Users/rosemary/Documents/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: CATALINA_HOME:         /opt/apache-tomcat-9.0.0.M21
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dcatalina.base=/Users/rosemary/Documents/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dcatalina.home=/opt/apache-tomcat-9.0.0.M21
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dwtp.deploy=/Users/rosemary/Documents/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Djava.endorsed.dirs=/opt/apache-tomcat-9.0.0.M21/endorsed
Jun 20, 2017 12:29:09 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dfile.encoding=UTF-8
Jun 20, 2017 12:29:09 PM org.apache.catalina.core.AprLifecycleListener lifecycleEvent
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [/Users/rosemary/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.]
Jun 20, 2017 12:29:10 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-nio-8080"]
Jun 20, 2017 12:29:10 PM org.apache.tomcat.util.net.NioSelectorPool getSharedSelector
INFO: Using a shared selector for servlet write/read
Jun 20, 2017 12:29:10 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-nio-8009"]
Jun 20, 2017 12:29:10 PM org.apache.tomcat.util.net.NioSelectorPool getSharedSelector
INFO: Using a shared selector for servlet write/read
Jun 20, 2017 12:29:10 PM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 1553 ms
Jun 20, 2017 12:29:10 PM org.apache.catalina.core.StandardService startInternal
INFO: Starting service [Catalina]
Jun 20, 2017 12:29:10 PM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/9.0.0.M21
Jun 20, 2017 12:29:11 PM org.apache.jasper.servlet.TldScanner scanJars
INFO: At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
Jun 20, 2017 12:29:11 PM org.apache.jasper.servlet.TldScanner scanJars
INFO: At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
Jun 20, 2017 12:29:11 PM org.apache.jasper.servlet.TldScanner scanJars
INFO: At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
Jun 20, 2017 12:29:11 PM org.apache.jasper.servlet.TldScanner scanJars
INFO: At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
Jun 20, 2017 12:29:11 PM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-nio-8080"]
Jun 20, 2017 12:29:11 PM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["ajp-nio-8009"]
Jun 20, 2017 12:29:11 PM org.apache.catalina.startup.Catalina start
INFO: Server startup in 1488 ms
Tue Jun 20 12:29:18 BST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Tue Jun 20 12:29:26 BST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.

这里没有打印任何异常。这会导致超时。评级的 MySQL 值是 int，反馈是 varchar。

Answer 1

您不应使用 JOptionPane 向用户提供反馈。 JOptionPane（Swing 框架）用于独立客户端。您正在编写一个 servlet，因此客户端是一个浏览器。您应该使用 response.getWriter() 来获取作家，然后使用 writer.println(""); ...writer.println("");做你的输出。

也许 JOptionPane 导致了错误（检查您的服务器日志），因此 SQL 更新语句未提交。所以对数据库没有影响。

Answer 2

LAST_INSERT_ID() 出于某种原因返回 0，因此 SQL 查询从未工作，这就是它从未进入异常的原因。