[英]Retrieve DB data with Java servlet and HTML form
我创建了一个简单的表单和一个小servlet,以从浏览器执行SQL语句。 当我单击表单上的“提交查询”按钮时,然后returinig页显示未从数据库检索到任何内容。 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>
您的类路径缺少jdbc驱动程序。 这可能有两个原因:
您知道您打开了数据库的后门吗? 数据库引擎检查数据库请求的源。 现在,请求来自您的网络服务器。 每台有权访问您网页的计算机都将连接到您的数据库。
您应该更改代码:
PreparedStatement
代替Statement
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