Java 按姓氏从学生订单中选择*； List students=new ArrayList（）； try（Connection con=dataSource.getConnection（）； PreparedStatement ps=con.prepareStatement（sql））{ //如有必要，在此处设置参数 //示例：“stmt.setInt（1，id）；”表示“其中id=？” try（ResultSet rs=ps.executeQuery（））{ while（rs.next（））{ int id=rs.getInt（“id”）； String firstName=rs.getString（“first_name”）； String lastName=rs.getString（“last_name”）； String email=rs.getString（“电子邮件”）； 添加（新学生（id、名字、姓氏、电子邮件））； } } } 留学生； } }
PS：尽量避免使用my和for属性名和变量名的前缀，因为它们不会添加任何信息。保持一致并使用有意义的名称总是好的。这就是我在上面的代码段中更改了一些名称的原因。也许HashSet可以帮到你？使用它而不是列表。你应该定义要使用的hashCode和equals方法龙目山可以帮你轻松完成Java 按姓氏从学生订单中选择*； List students=new ArrayList（）； try（Connection con=dataSource.getConnection（）； PreparedStatement ps=con.prepareStatement（sql））{ //如有必要，在此处设置参数 //示例：“stmt.setInt（1，id）；”表示“其中id=？” try（ResultSet rs=ps.executeQuery（））{ while（rs.next（））{ int id=rs.getInt（“id”）； String firstName=rs.getString（“first_name”）； String lastName=rs.getString（“last_name”）； String email=rs.getString（“电子邮件”）； 添加（新学生（id、名字、姓氏、电子邮件））； } } } 留学生； } },java,Java,PS：尽量避免使用my和for属性名和变量名的前缀，因为它们不会添加任何信息。保持一致并使用有意义的名称总是好的。这就是我在上面的代码段中更改了一些名称的原因。也许HashSet可以帮到你？使用它而不是列表。你应该定义要使用的hashCode和equals方法龙目山可以帮你轻松完成 package com.luv2code.web.jdbc; import java.io.IOException; import java.util.List; import javax.annotation.
package com.luv2code.web.jdbc;
import java.io.IOException;
import java.util.List;
import javax.annotation.Resource;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
/**
* Servlet implementation class StudentControllerServlet
*/
@WebServlet("/StudentControllerServlet")
public class StudentControllerServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private StudentDButil studentDbUtil;
@Resource(name="jdbc/web_student_tracker")
private DataSource dataSource;
@Override
public void init() throws ServletException {
super.init();
// create our student db util ... and pass in the conn pool / datasource
try {
studentDbUtil = new StudentDButil(dataSource);
}
catch (Exception exc) {
throw new ServletException(exc);
}
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
listStudents(request,response);
} catch(Exception e) {
throw new ServletException(e);
}
}
private void listStudents(HttpServletRequest request, HttpServletResponse response)
throws Exception {
// get students from db util
List<Student> students = studentDbUtil.getStudent();
// add students to the request
request.setAttribute("STUDENT_LIST", students);
// send to JSP page (view)
RequestDispatcher dispatcher = request.getRequestDispatcher("/list-students.jsp");
dispatcher.forward(request, response);
}
}
<%@ page import="java.util.*,com.luv2code.web.jdbc.*" %>
<!DOCTYPE html>
<html>
<head>
Student Tracker App
</head>
<% List<Student> theStudent=(List<Student>)request.getAttribute("STUDENT_LIST"); %>
<body>
<%= theStudent %>
</body>
</html>
package com.luv2code.web.jdbc;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import javax.sql.DataSource;
public class StudentDButil {
List<Student> students = new ArrayList<>();
private DataSource datasources;
public StudentDButil (DataSource thedatasources)
{
datasources = thedatasources;
}
public List<Student> getStudent() throws Exception
{
Connection mycon = null;
Statement mystmt = null;
ResultSet myres = null;
try {
mycon = datasources.getConnection(); //get DB connection
String sqlStmt = "select * from student order by last_name"; //write an sql statement
mystmt = mycon.createStatement(); //create sql statement
myres = mystmt.executeQuery(sqlStmt); //execute query
while(myres.next())
{
//retrive data from resultset
int id = myres.getInt("id");
String fname = myres.getString("first_name");
String lname = myres.getString("last_name");
String emailid = myres.getString("email");
Student std = new Student(id, fname, lname, emailid); //create student object
students.add(std); //add student object to list
}
return students;
}
finally
{
close(mycon, mystmt, myres); //close jdbc connections
}
}
private void close(Connection mycon, Statement mystmt, ResultSet myres) {
try {
if(myres!=null)
{
myres.close();
}
if(mystmt!=null)
{
mystmt.close();
}
if(mycon!=null) {
mycon.close(); //dosen't really close it. just puts back into the connection pool
}
}
catch(Exception exc)
{
exc.printStackTrace();
}
}
//get DB connection
}
public class StudentDbUtil {
private final DataSource dataSource;
public StudentDbUtil(DataSource dataSource) {
this.dataSource = dataSource;
}
public List<Student> getStudent() throws SQLException {
String sql = "select * from student order by last_name";
List<Student> students = new ArrayList<>();
try (Connection con = dataSource.getConnection();
PreparedStatement ps = con.prepareStatement(sql)) {
// set parameters here if necessary
// example: "stmt.setInt(1, id);" for "WHERE id=?"
try (ResultSet rs = ps.executeQuery()) {
while (rs.next()) {
int id = rs.getInt("id");
String firstName = rs.getString("first_name");
String lastName = rs.getString("last_name");
String email = rs.getString("email");
students.add(new Student(id, firstName, lastName, email));
}
}
}
return students;
}
}