[英]Connect to mysql database from servlet
我正在尝试连接到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:
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? 这些标准吗? 如果没有,我该如何找到与我的数据库相对应的数据库。 同样,在创建数据库时,也没有要求我输入用户名和密码。
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 **
网址告诉程序在哪里以及如何查找数据库。 在这种情况下,您将使用JDBC访问在您自己的计算机( localhost
)上运行的MySQL数据库。
dbname是数据库的名称。 MySQL服务器可能托管多个数据库,因此您需要指定所需的数据库。
驱动程序是将用于访问数据库的Java类。
用户名和密码说明自己。
假设url中的端口和数据库名称正确,则您的问题很可能是用户名/密码组合。 默认情况下,用户名是“ root”,密码是空的。
是的,所有这些都是标准的,您必须使用它通过java连接到数据库。
//since you have to connect to database you have to connect through to database server with url(where localhost signifies your current system and 3306 is a port)
String url = "jdbc:mysql://localhost:3306/";
//In order to connect to specific database specify its name
String dbName = "LoginExample";
//Initialize a driver so you can open a communications channel with the database.
String driver = "com.mysql.jdbc.Driver";
//credentials required to connect
String userName = "root";
String password = "password"
由于您在安装过程中输入了任何用户名和密码,因此设置了默认名称和密码。默认用户名是root
,密码是no password。您还可以重设密码 。
com.mysql.jdbc.CommunicationsException:由于基础异常导致通信链接失败:
首先,您不需要实例化驱动程序,只需调用它的静态初始化(例如,通过调用Class.forName),即可在DriverManager中注册它。
因此,从Class.forName(driver).newInstance()
删除.newInstance()
Class.forName(driver).newInstance()
;
还要检查端口3306是否被其他进程获取
运行 resmon.exe
并转到“网络”选项卡,以检查3306端口是否被其他进程获取。
您不应该手动尝试从servlet建立数据库连接。 相反,您应该定义一个DataSource
并从servlet中查找它。
Tomcat逐步指南:
/lib
文件夹中 在Tomcat的context.xml
定义数据源
< 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
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:
InitialContext ctx = new InitialContext(); DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/DefaultDB");
或者,您可以注入数据源:
@Resource(name="jdbc/DefaultDB") private javax.sql.DataSource ds;
获取连接:
Connection connection = ds.getConnection();
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