java - Spring MVC - 在浏览器中显示来自数据库的数据

Question

如标题所示，我想在浏览器中使用 Spring MVC 帮助显示来自数据库的数据。

我在 Spring 中创建动态 Web 项目，写了几行代码，它不起作用:x

当我在本地 srv Tomcat v8.5 上运行它时，它只显示我制作的列 - 没有数据:/

有人可以看看我的代码吗？你有没有看错？

顺便说一句。它是在 Spring 中用 .jsp 文件编写的。

感谢您的帮助!

   <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@page import="java.sql.*"%>
<%@page import="java.sql.DriverManager"%>
<%@page import="java.sql.ResultSet"%>
<%@page import="java.sql.Statement"%>
<%@page import="java.sql.Connection"%>

<%
    try {
        Class.forName("org.postgresql.Driver");
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
    Connection connection = null;
    Statement statement = null;
    ResultSet resultSet = null;
%>
<h2 align="center">
    <font><strong>Retrieve data from database in jsp</strong></font>
</h2>
<table align="center" cellpadding="5" cellspacing="5" border="1">
    <tr>
    </tr>
    <tr bgcolor="#A52A2A">
        <td><b>id</b></td>
        <td><b>user_id</b></td>
        <td><b>Password</b></td>
        <td><b>Name</b></td>
        <td><b>Email</b></td>
    </tr>
    <%
        try {
              connection=DriverManager.getConnection("jdbc:postgresql://localhost:5432/serie_db","postgres","admin");
        statement = connection.createStatement();
        String sql = "SELECT * FROM serie";

        resultSet = statement.executeQuery(sql);
        while (resultSet.next()) {
%>
<tr bgcolor="#DEB887">

    <td><%=resultSet.getString("id")%></td>
    <td><%=resultSet.getString("name")%></td>
    <td><%=resultSet.getString("datefrom")%></td>
    <td><%=resultSet.getString("dateto")%></td>
    <td><%=resultSet.getString("feed")%></td>
</tr>
<%
    }
        connection.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
%>
</table>

编辑:这是我的错误日志 技巧如: 项目/属性/projectFacets/runtime/- 完成... 导入 lib postgresql-42.0.0.jar - 完成

java.lang.ClassNotFoundException: org.postgresql.Driver
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1285)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1119)
at org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:123)
at org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:60)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:131)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
java.sql.SQLException: No suitable driver found for     jdbc:postgresql://localhost:5432/serie_db
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:156)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

Answer 1

您的问题似乎是您没有将 postgresSQL 驱动程序添加到项目类路径中。然后 Tomcat 找不到驱动程序来访问您的数据库。

但更重要的是，这个错误是您没有遵守 MVC(模型- View - Controller )模式，您永远不应该直接从 View 访问数据库，您需要访问 Controller ，而 Controller 将委托(delegate)给适当的服务来完成该任务。

我认为如果您从这个示例开始从头开始会很好 Web app example

它很简单，你会很快地工作。