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最新推荐文章于 2023-12-13 09:28:55 发布

原创最新推荐文章于 2023-12-13 09:28:55 发布 · 217 阅读

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本文介绍了在Java中使用数据库连接池进行资源管理和关闭数据库连接的常见实践，包括如何正确地初始化连接、获取连接以及在操作后关闭并释放连接资源，以避免资源泄漏和异常情况。

connection.close()会释放该链接资源。但是connection！=null。一般要在close后将其引用置空（connection=null).为了避免它报数据库连接关闭之后不允许操作的错。
如：
——————-DbHelp.java———————–

package com;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DbHelp {
public static final String username = “root”;
public static final String password = “root”;
public static final String driver=”com.mysql.jdbc.Driver”;
public static final String url=”jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8”;
public static Connection conn=null;
static{
try {
Class.forName(driver);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public static Connection getConnection() throws SQLException {
if (conn == null) {
conn=DriverManager.getConnection(url, username, password);
return conn;
}else{
return conn;
}
}
public static void close(){
if (conn != null) {
try {
conn.close();
conn=null;
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/**测试连接
public static void main(String args[]) {
try {
Connection conn= DbHelp.getConnection();
System.out.println(“连接成功”);
} catch (SQLException e) {
System.out.println(“数据库连接失败”);
e.printStackTrace();
}
}

**/
}

——————–LoginServlet.java—————————
package servlet;
import com.DbHelp;
import com.sun.org.apache.xpath.internal.operations.Bool;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class LoginServlet extends HttpServlet {
private Connection conn;
private PreparedStatement ps;
private ResultSet rs;

public LoginServlet() {
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String username = request.getParameter("username");
    String psd = request.getParameter("password");
    System.out.println("password:"+psd);
    boolean flag = false;//标志着应该登录成功还是登录失败
    if (username == null || username.trim().equals("")) {//如果用户名为空
        request.setAttribute("msg", "请填写用户名");
    } else if (psd == null || psd.trim().equals("")) {//如果密码为空
        request.setAttribute("msg", "请输入密码");
    } else {
        try {
            conn = DbHelp.getConnection();
            ps = conn.prepareStatement("SELECT password FROM admin WHERE username=?");
            ps.setString(1, username);
            rs = ps.executeQuery();
            if (rs.next()) {
                String spsd = rs.getString("password");
                System.out.println("spsd:"+spsd);
                if (!spsd.equals(psd)) {//如果查询结果不为空，但密码不正确
                    request.setAttribute("msg", "密码错误");
                } else {//如果密码正确
                    request.getSession().setAttribute("loginFlag", "sucess");
                    flag = true;
                }
            } else {//如果查询结果为空（即没有此用户）
                request.setAttribute("msg", "不存在此用户");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                rs.close();
                ps.close();
                DbHelp.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    if (flag) {
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    } else {
        request.getRequestDispatcher("/sign/login.jsp").forward(request, response);
    }
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request, response);
}

}