分三步：
1、到tomcat目錄下conf資料夾裡面的server.xml部署專案
2、到tomcat目錄下conf資料夾裡面的context.xml設定資料庫連線
3、專案內寫呼叫context.xml的類

server.xml

<Context path="/專案名" docBase="專案路徑" reloadable="true">
</Context>

context.xml

<Resource
    name="jdbc/專案名"
    auth="Container"
    type ="javax.sql.DataSource"
    driverClassName = "com.mysql.jdbc.Driver"
 

    url = "jdbc:mysql://localhost:3306/xxxxx"
    username = "dbuser"
    password = "dbpassword"
/>

DbBean.java(先匯入mysql的連線jar包到專案中)

import java.sql.*;
import javax.sql.*;

public class DbBean {

    private Connection dbCon;

    String dbURL = "jdbc:mysql://localhost:3306/xxxxx";
    String dbDriver = "com.mysql.jdbc.Driver"
 
 ;
    String dbUser = "dbuser";
    String dbPassword = "dbpassword";

    public DbBean() {
        super();
    }

    public boolean connect() throws ClassNotFoundException, SQLException {

        try{
            Context initCtx = new InitialContext();
            if(initCtx == null ){
                throw
 
 new Exception("No Context");
            }
            Context ctx = (Context) initCtx.lookup("java:comp/env");
            DataSource ds = (DataSource)ctx.lookup("jdbc/專案名");  //專案名要與context.xml裡面的對應
            if(ds != null){
                dbCon = ds.getConnection();
                dbCon.setAutoCommit(false);
                return true;
            }else{
                return false;
            }  
        }catch(javax.naming.NoInitialContextException e){   //以防萬一 tomcat上配置的context.xml用不了
            Class.forName(this.getDbDriver());
            dbCon = DriverManager.getConnection(this.getDbURL() , dbUser ,dbPassword);
            dbCon.setAutoCommit(false);
            return true;
        }catch(Exception e){
            return false;
        }

    }

}

到這裡就已經可以連線資料庫了 剩下的就是在DbBean裡面加上自己要的程式碼