从Servlet到JSP显示MySQL查询结果 [英] Displaying MySQL Query Results from Servlet to JSP
问题描述
我正在尝试将查询结果存储在字符串中，并通过将该字符串传递给它来将它们打印到JSP页面的底部。现在，JSP页面最初显示正常，但是当我单击按钮发布命令时没有发生任何事情。早些时候，当我从一个html页面访问servlet，并使用PrintWriter将所有输出打印出来时，我得到了显示的结果，但它们会显示在一个单独的页面上。
I am trying to store the results of my query in a string, and print them to the bottom of my JSP page by passing that string to it. Right now, the JSP page displays fine initially, but nothing is happening when I click the button to post the command. Earlier when I accessed the servlet from an html page, and printed all my output to out using a PrintWriter, I got the results to display, but they would display on a separate page.
1）以这种方式存储是一个好主意，还是应该使它与字符串不同？
1) Is it a good idea to store out in this way, or should I make it something different than a string?
2）我如何获得查询结果发布到JSP页面？
2) How do I get the results of the query to post to the JSP page?
databaseServlet.java
databaseServlet.java
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.sql.*;
@SuppressWarnings("serial")
public class databaseServlet extends HttpServlet {
private Connection conn;
private Statement statement;
public void init(ServletConfig config) throws ServletException {
try {
Class.forName(config.getInitParameter("databaseDriver"));
conn = DriverManager.getConnection(
config.getInitParameter("databaseName"),
config.getInitParameter("username"),
config.getInitParameter("password"));
statement = conn.createStatement();
}
catch (Exception e) {
e.printStackTrace();
}
}
protected void doPost (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String out = "\n";
String query = request.getParameter("query");
if (query.toString().toLowerCase().contains("select")) {
//SELECT Queries
try {
ResultSet resultSet = statement.executeQuery(query.toString());
ResultSetMetaData metaData = resultSet.getMetaData();
int numberOfColumns = metaData.getColumnCount();
for(int i = 1; i<= numberOfColumns; i++){
out.concat(metaData.getColumnName(i));
}
out.concat("\n");
while (resultSet.next()){
for (int i = 1; i <= numberOfColumns; i++){
out.concat((String) resultSet.getObject(i));
}
out.concat("\n");
}
}
catch (Exception f) {
f.printStackTrace();
}
}
else if (query.toString().toLowerCase().contains("delete") || query.toLowerCase().contains("insert")) {
//DELETE and INSERT commands
try {
conn.prepareStatement(query.toString()).executeUpdate(query.toString());
out = "\t\t Database has been updated!";
}
catch (Exception l){
l.printStackTrace();
}
}
else {
//Not a valid response
out = "\t\t Not a valid command or query!";
}
RequestDispatcher dispatcher = request.getRequestDispatcher("/dbServlet.jsp");
dispatcher.forward(request, response);
request.setAttribute("queryResults", out);
}
}
dbServlet.jsp
dbServlet.jsp
<?xml version = "1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!-- dbServlet.html -->
<html xmlns = "http://www.w3.org/1999/xhtml">
<head>
<title>MySQL Servlet</title>
<style type="text/css">
body{background-color: green;}
</style>
</head>
<body>
<h1>This is the MySQL Servlet</h1>
<form action = "/database/database" method = "post">
<p>
<label>Enter your query and click the button to invoke a MySQL Servlet
<textarea name = "query" cols="20" rows="5"></textarea>
<input type = "submit" value = "Run MySQL Servlet" />
<input type = "reset" value = "Clear Command" />
</label>
</p>
</form>
<hr>
<%=
request.getAttribute("queryResults");
%>
</body>
</html>
推荐答案
dispatcher.forward(request, response);
request.setAttribute("queryResults", out);
应该是这样的
request.setAttribute("queryResults", out);
dispatcher.forward(request, response);
在调度请求之前，必须设置属性
Before the request is dispatched the attributes has to be set
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