Question

我正在使用Windows 8.1 64位操作系统，oracle 12c数据库和netbeans ide.i在我的netbeans IDE中创建了一个名为 WebApplication1 的java Web项目。在我的数据库中，我创建了一个用户 C ## abc 和密码 abc ，数据库SID为 orcl 。在我的数据库中，我创建了一个名为 city 的表，列名为地址，并将一个数据“xyz”插入表格城市。我在文本框中编写城市后运行项目并在浏览器中收到消息 - Servlet NewServlet at / WebApplication1 但它应显示 xyz 。我哪里错了？

我添加了2个jar苍蝇ojdbc14.jar和ojdbc_14.jar文件。

我的new.jsp

<form action="NewServlet" method="post">
<font face="verdana" size="2">
Enter Table Name :<input type="text" name="table"> 
                   <input type="submit" value="Display">
</font>
</form>

NewServlet.java

package p;

import java.io.IOException;
import java.io.PrintWriter;
import static java.lang.System.out;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class NewServlet extends HttpServlet {


/**
 * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
 * methods.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    try (PrintWriter out = response.getWriter()) {
        /* TODO output your page here. You may use following sample code. */
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet NewServlet</title>");            
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Servlet NewServlet at " + request.getContextPath() + "</h1>");
        out.println("</body>");
        out.println("</html>");
    }
}

// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
/**
 * Handles the HTTP <code>GET</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

/**
 * Handles the HTTP <code>POST</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse  response)
        throws ServletException, IOException {
    String tb=request.getParameter("table");     

    try
    {
         Class.forName("oracle.jdbc.driver.OracleDriver");
         Connection
   con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl","c##abc","abc");
         Statement st=con.createStatement();
      out.println("connection established successfully...!!");     

         ResultSet rs=st.executeQuery("Select * from "+tb);


             while(rs.next())
             {
          out.println(rs);              }

    }
    catch (ClassNotFoundException | SQLException ex){
       out.println(ex);
    }

Answer 1

在doPost()方法中，您使用的out为System.out，已导入（作为静态）。在processRequest()中，您可以使用以下内容覆盖它：

PrintWriter out = response.getWriter()

...这有点令人困惑，我会选择一个不同的变量名称。但是你没有在doPost().中这样做，所以你用println在该方法中写的任何东西都是通过HttpServletResponse对浏览器做的，它只是去JVM控制台。

从您发布的代码中，processRequest()如何被调用并不明显 - 您必须看到所获得的输出。你没有从该方法中显示对doGet() / processRequest()的调用，或者servlet处理正在自动回退到doGet()，因为响应尚未启动，或者它正在重定向在错误情况发生后自动回复。

即使使用response.getWriter()的本地变量，您也需要发送正确的HTML，而不仅仅是现在的简单非标记消息，否则您只会得到一个空白页。

servlet oracle数据库连接示例

1 个答案: