注意：

>我已经在我的网站上加入了“MysqL-connector-java-5.1.25-bin.jar”
classpath via：export
CLASSPATH = $CLASSPATH：/home/me/ocpjp/chapter-10/MysqL-connector-java-5.1.25/MysqL-connector-java-5.1.25-bin.jar
>我能够使用“MysqL -uroot -ptcial”连接到MysqL
地址簿“,如果重要的话.
>还尝试使用’-cp’运行
争论无济于事.
>我能够让我的#3 DbConnect.java类说“已建立数据库连接”.
>#4 DbQueryWorking.java没有问题,并提供预期的输出.

你能帮我理解这里的问题吗？

1)DbConnector.java

package com.me.ocpjp.chapter10;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.sqlException;

public class DbConnector{
public static Connection connectToDb() throws sqlException{
String url = "jdbc:MysqL//localhost:3306/";
String db = "addressBook";
String username = "root";
String password = "tcial";
return DriverManager.getConnection(url+db,username,password);
}

}

2)DbQuery.java

package com.me.ocpjp.chapter10;

import java.sql.Connection  ;
import java.sql.Statement  ;
import java.sql.ResultSet  ;
import java.sql.sqlException  ;
import com.me.ocpjp.chapter10.DbConnector;

public class DbQuery{
public static void main(String[] args){
try(Connection connection = DbConnector.connectToDb();
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("select * from contact")){
System.out.println("ID \tfName \tlName \temail \t\tphoneNo");
while(resultSet.next()){
System.out.println(resultSet.getInt("id") + "\t"
+ resultSet.getString("firstName") + "\t"
+ resultSet.getString("lastName") + "\t"
+ resultSet.getString("email") + "\t"
+ resultSet.getString("phoneNo") );
}

}catch(sqlException sqle){
sqle.printStackTrace();
System.exit(-1);
}

}
}

3)DbConnect.java

package com.me.ocpjp.chapter10;

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



public class DbConnect{
public static void main(String[] args){

String url = "jdbc:MysqL://localhost:3306/";
String database = "addressBook";
String userName = "root";
String password = "tcial";

try(Connection connection = DriverManager.getConnection(url+database,userName,password)){
System.out.println("Database connection established");
}catch(Exception e){
System.out.println("Database connectioni NOT  established");
e.printStackTrace();
}

}

}

4)DbQueryWorking.java

package com.me.ocpjp.chapter10;

import java.sql.Connection  ;
import java.sql.Statement  ;
import java.sql.ResultSet  ;
import java.sql.sqlException  ;
import java.sql.DriverManager;

public class DbQuery{
public static void main(String[] args){
String url = "jdbc:MysqL://localhost:3306/";
String database = "addressBook";
String userName = "root";
String password = "tcial";
try(Connection connection = DriverManager.getConnection(url + database,password);
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("select * from contact")){
System.out.println("ID \tfName \tlName \temail \t\tphoneNo");
while(resultSet.next()){
System.out.println(resultSet.getInt("id") + "\t"
+ resultSet.getString("firstName") + "\t"
+ resultSet.getString("lastName") + "\t"
+ resultSet.getString("email") + "\t"
+ resultSet.getString("phoneNo") );
}

}catch(sqlException sqle){
sqle.printStackTrace();
System.exit(-1);
}

}
}