📄 addusers.java
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package com.v512.guestbook;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class AddUsers extends HttpServlet {
private static final long serialVersionUID = 1L;
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String driver= "org.postgresql.Driver" ;
String url = " jdbc:postgresql://localhost:5432/postgres" ;
String sql = "insert into users (username,password) values(?,?)";
String username = "postgres";
String password = "123456";
Connection conn = null;
//int result = 0;
String name = request.getParameter("username");
String pass = request.getParameter("password");
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head><title>users input page</title></head>");
out.println("<body>");
if (StringUtil.validateNull(name)) {
out.println("对不起，姓名不能为空");
out.println("<a href=\""+request.getContextPath()+"/login.htm\">请重新输入</a><br>");
} else if (StringUtil.validateNull(pass)) {
out.println("对不起，密码不能为空，");
out.println("<a href=\""+request.getContextPath()+"/login.htm\">请您重新输入！</a><br>");
} else {
try {
Class.forName(driver);
conn = DriverManager.getConnection(url,username,password);
PreparedStatement pstmt1 = conn.prepareStatement("select * from users where username='"+name+"'");
ResultSet rs = pstmt1.executeQuery();
PreparedStatement pstmt = conn.prepareStatement(sql);
if(rs.next()) {
out.println("对不起，用户名已经存在，请您重新输入！<br>");
out.println("<a href=\""+request.getContextPath()+"/login.htm\">重试</a><br>");
return ;
}
else{
pstmt.setString(1, StringUtil.filterHtml(name));
pstmt.setString(2, StringUtil.filterHtml(pass));
pstmt.executeUpdate();
out.println("祝贺您，注册成功！<br>");
out.println("<a href=\""+request.getContextPath()+"/addMessage.htm\">添加留言</a><br>");
out.println("浏览用户列表");
out.println("<a href=\"" + request.getContextPath() + "/servlet/getUsers\">最近注册用户列表</a><br>");
}
pstmt1.close();
pstmt.close();
conn.close();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
catch (SQLException e) {
e.printStackTrace();
}
/*if (result == 0) {
out.println("对不起，注册失败，");
out.println("<a href=\""+request.getContextPath()+"/login.htm\"> 请重试！</a><br>");
} else {*/
out.println("</body>");
out.println("</html>");
out.flush();
out.close();
}
}
}
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