从servlet连接到mysql数据库 [英] Connect to mysql database from servlet

问题描述

我正在尝试连接到我的数据库以检查用户名和密码.我正在学习教程，但我的连接无法正常工作.我的问题在以下几行:

I am trying to connect to my database in order to check a username and password. I am following a tutorial but my connection is not working. My question are in these lines:

String url = "jdbc:mysql://localhost:3306/"; 
String dbName = "LoginExample";
String driver = "com.mysql.jdbc.Driver";  
String userName = "root";  
String password = "password"; 

所有这些值的含义是什么?那些是标准的吗?如果不是，我怎么能找到哪些对应于我的数据库.我在创建数据库时也没有被要求输入用户名和密码.

What is the meaning of all those values? Are those standard? If not how can I find which ones correspond to my database. Also I wasn't asked for a username and password when I created my database.

public class Login extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Login() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

    public static boolean validate(String name, String pass) {
        boolean status = false;
        Connection conn = null;
        PreparedStatement pst = null;
        ResultSet rs = null;

        String url = "jdbc:mysql://localhost:3306/"; 
        String dbName = "LoginExample";
        String driver = "com.mysql.jdbc.Driver";  
        String userName = "root";  
        String password = ""; 

        try {  
            Class.forName(driver).newInstance();  
            conn = DriverManager  
                    .getConnection(url + dbName, userName, password);  

            pst = conn  
                    .prepareStatement("select * from Users where username=? and password=?");  
            pst.setString(1, name);  
            pst.setString(2, pass);  

            rs = pst.executeQuery();  
            status = rs.next();  

        } catch (Exception e) {  
            System.out.println(e);  
        } finally {  
            if (conn != null) {  
                try {  
                    conn.close();  
                } catch (SQLException e) {  
                    e.printStackTrace();  
                }  
            }  
            if (pst != null) {  
                try {  
                    pst.close();  
                } catch (SQLException e) {  
                    e.printStackTrace();  
                }  
            }  
            if (rs != null) {  
                try {  
                    rs.close();  
                } catch (SQLException e) {  
                    e.printStackTrace();  
                }  
            }  
        }
        return status;
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String un = request.getParameter("username");
        String pw = request.getParameter("password");

        response.setContentType("text/html");    
        PrintWriter out = response.getWriter();  

        HttpSession session = request.getSession(false);
        if (session != null) {
            session.setAttribute("name", un);
        }

        if (validate(un,pw)) {
            RequestDispatcher rd=request.getRequestDispatcher("welcome.jsp");    
            rd.forward(request,response); 
        } else {
            out.print("<p style=\"color:red\">Sorry username or password error</p>"); 
        }
    }

}

错误日志:

com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception: 

** BEGIN NESTED EXCEPTION ** 

java.net.ConnectException
MESSAGE: Connection refused: connect

STACKTRACE:

java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
    at java.net.PlainSocketImpl.connect(Unknown Source)
    at java.net.SocksSocketImpl.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at java.net.Socket.<init>(Unknown Source)
    at java.net.Socket.<init>(Unknown Source)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:271)
    at com.mysql.jdbc.Connection.createNewIO(Connection.java:2771)
    at com.mysql.jdbc.Connection.<init>(Connection.java:1555)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at servlets.Login.validate(Login.java:55)
    at servlets.Login.doPost(Login.java:112)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)


** END NESTED EXCEPTION **

推荐答案

您不应该手动尝试从您的 servlet 建立数据库连接.相反，您应该定义一个 DataSource 并从您的 servlet 中查找它；

You should not manually try to establish database connection from your servlet. Instead you should define a DataSource and look it up from your servlet;

tomcat 的分步指南:

Step by step guide for tomcat:

1. 把你的mysql驱动放到tomcat的/lib文件夹

2. 在Tomcat的context.xml中定义一个数据源

1. Put your mysql driver in tomcat's /lib folder

2. Define a datasource in Tomcat's context.xml

< Resource name="jdbc/DefaultDB"
      type="javax.sql.DataSource"  auth="Container"
      description="Default datasource"
      maxActive="100" maxIdle="30" maxWait="10000"
      username="" password="" 
      driverClassName="com.mysql.jdbc.Driver"
      url="com.mysql.jdbc.Driver"/>

在您的 web.xml 中引用此数据源

< resource-ref>  
        < res-ref-name>jdbc/DefaultDB</res-ref-name>  
        < res-type>javax.sql.DataSource</res-type>  
        < res-auth>Container</res-auth>  
< /resource-ref >

查找数据源:

Look up the data source:

InitialContext ctx = new InitialContext();DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/DefaultDB");

作为替代，您可以注入数据源:

As an alternative you can inject the data source:

@Resource(name="jdbc/DefaultDB")私有 javax.sql.DataSource ds;

获取连接:

Connection connection = ds.getConnection();

这篇关于从servlet连接到mysql数据库的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！