Question

我创建了一个简单的表单和一个小的servlet来从浏览器执行SQL语句。当我单击表单上的“提交查询”按钮时，返回页面显示没有从数据库中检索到任何内容。它仅在浏览器上显示“数据库结果”（标记部分）。请告诉我我的代码有什么问题。

SQLTestForm.java

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class SQLTestForm extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        String title = "Results";
        String docType = 
            "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " + "Transitional//EN\"\n";
            out.print(docType + "<HTML>\n" + "<HEAD><TITLE>" + title + "</TITLE></HEAD>\n" + "<BODY>" + "<H1>Database Results</H1>\n");

        String driver = request.getParameter("driver");
        String url = request.getParameter("url");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String qry = request.getParameter("query");
        showTable(driver, url, username, password, qry, out);
        out.println("</BODY></HTML>");
    }

  public void showTable(String driver, String url, String username, String password, String qry, PrintWriter out) {
    try {
    Class.forName(driver);
    Connection conn = DriverManager.getConnection(url, username, password);
    DatabaseMetaData dbMetaData = conn.getMetaData();
    out.println("<UL>");
    String productName = dbMetaData.getDatabaseProductName();
    String productVersion = dbMetaData.getDatabaseProductVersion();
    out.println(" <LI><B>Database:</B> " + productName + " <LI><B>Version:</B> " + productVersion + "</UL>");
    Statement stmt = conn.createStatement();
    ResultSet rs = stmt.executeQuery(qry);
    out.println("<TABLE BORDER=1>");
    ResultSetMetaData rm = rs.getMetaData();
    int cnum = rm.getColumnCount();
    out.println("<TR>");
        for(int i=1; i <= cnum; i++) {
            out.print("<TH>" + rm.getColumnName(i));
        }
        out.println();
        while(rs.next()) {
            out.println("<TR>");
                for(int i=1; i <= cnum; i++) {
                    out.print("<TD>" + rs.getString(i));
                }
            out.println();
        }
        out.println("</TABLE>");
        conn.close();
    } catch (ClassNotFoundException cnfe) {
        System.err.println("Error loading driver: " + cnfe);
    } catch (SQLException se) {
        System.err.println("Error connecting: " + se);
    } catch(Exception e) {
        System.err.println("Error with input: " + e);   }  } }

SQLTestForm.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
 <HEAD>
  <TITLE>SQL Test Form</TITLE>
 </HEAD>
 <BODY>
  <H2>Query Input:</H2>
  <FORM ACTION="/SQLTestForm" METHOD="POST">
  <TABLE>
   <TR><TD>Driver:
   <TD><INPUT TYPE="TEXT" NAME="driver" VALUE="com.jdbc.mysql.Driver" SIZE="45">
   <TR><TD>URL:
   <TD><INPUT TYPE="TEXT" NAME="url"
   VALUE="jdbc:mysql://localhost:3306/test" SIZE="45">
   <TR><TD>Username:
   <TD><INPUT TYPE="TEXT" NAME="username">
   <TR><TD>Password:
   <TD><INPUT TYPE="PASSWORD" NAME="password">
   <TR><TD VALIGN="TOP">Query:
   <TD><TEXTAREA ROWS="5" COLS="35" NAME="query"></TEXTAREA>
   <TR><TD COLSPAN="2" ALIGN="CENTER"><INPUT TYPE="SUBMIT">
  </TABLE>
  </FORM>
 </BODY>
</HTML>

Answer 1

您的类路径缺少jdbc驱动程序。这可能有两个原因：

您忘记在war-file或shared / commons-lib文件夹中传递deiver。
你错误拼写了驱动程序的Classname（你在评论中写了com.djbc而不是com.jdbc

你知道你打开数据库的后门吗？数据库引擎检查数据库请求的来源。现在请求来自您的网络服务器。有权访问您网页的每台计算机都将与您的数据库建立连接。

您应该更改代码：

切勿使用取消选中参数并将其传递给数据库。
使用PreparedStatement代替Statement
不要使用字符串连接来创建查询

使用Java servlet和HTML表单检索DB数据

1 个答案: