Question

我在下面的代码中有一个例外...我正在尝试构建一个简单的servlet项目，并且我引发了以下异常：java.net.UnknownHostException ...
我添加了mysql jar文件，除此之外......我已将其添加为外部jar文件，并在WEB-INF中的lib下添加，如this page中所述，但现在这是抛出java.net.UnknownHostException

这是代码和异常堆栈跟踪。

package com.servlet.Mysql;

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


public class Connection_Class {
String driver_ClassName="com.mysql.jdbc.Driver";
String URL_connection="jdbc:mysql://localhost3306/vendor";
String user="root";
String password="lifesuckzz";
private static Connection_Class connectionclass=null;

private Connection_Class(){
    try{
        Class.forName(driver_ClassName);

    }catch(ClassNotFoundException e){
        e.printStackTrace();
    }
}

public Connection getConnection() throws SQLException{
    Connection con=null;
    con=DriverManager.getConnection(URL_connection,user,password);
    return con;
}

public static Connection_Class getInstance(){
    if(connectionclass==null){
        connectionclass=new Connection_Class();
    }
    return connectionclass;}}

堆栈追踪：

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

** BEGIN NESTED EXCEPTION ** 

java.net.UnknownHostException
MESSAGE: localhost3306

STACKTRACE:

java.net.UnknownHostException: localhost3306
at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$1.lookupAllHostAddr(Unknown Source)
at java.net.InetAddress.getAddressesFromNameService(Unknown Source)
at java.net.InetAddress.getAllByName0(Unknown Source)
at java.net.InetAddress.getAllByName(Unknown Source)
at java.net.InetAddress.getAllByName(Unknown Source)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:133)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:280)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:1699)
at com.mysql.jdbc.Connection.<init>(Connection.java:405)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:268)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at com.servlet.Mysql.Connection_Class.getConnection(Connection_Class.java:25)
at com.servlet.Mysql.LoginServlet.doGet(LoginServlet.java:49)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)


** END NESTED EXCEPTION **


at com.mysql.jdbc.Connection.createNewIO(Connection.java:1764)
at com.mysql.jdbc.Connection.<init>(Connection.java:405)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:268)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at com.servlet.Mysql.Connection_Class.getConnection(Connection_Class.java:25)
at com.servlet.Mysql.LoginServlet.doGet(LoginServlet.java:49)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

我正在使用Apache Web容器和Eclipse，这篇文章java.lang.ClassNotFoundException in spite of using CLASSPATH environment variable我认为这里的情况并不接近我.....请帮帮我，谢谢你们提前...

Answer 1

您错过了主机名和端口号之间的冒号...您的连接网址应为

String URL_connection="jdbc:mysql://localhost:3306/vendor";

Answer 2

我认为连接网址应为jdbc:mysql://localhost:3306/vendor。 localhost是服务器名称，3306端口名称由:分隔。

String URL_connection="jdbc:mysql://localhost:3306/vendor";

请浏览docs。

MySQL Connector / J的JDBC URL格式如下，方括号（[，]）中的项是可选的：

jdbc:mysql://[host][,failoverhost...][:port]/[database] »
[?propertyName1][=propertyValue1][&propertyName2][=propertyValue2]...

如果未指定主机名，则默认为127.0.0.1。如果未指定端口，则默认为3306 。

数据库连接 - java.net.UnknownHostException

2 个答案: