java - java.sql.SQLException：找不到合适的驱动程序

Question

我正在尝试使用下面的 DbQuery.java 类执行简单查询，该类使用 DbConnector 从 DriverManager 获取连接。

注意：

1. 我已经通过以下方式在我的类路径中包含了“mysql-connector-java-5.1.25-bin.jar”：export CLASSPATH=$CLASSPATH:/home/me/ocpjp/chapter-10/mysql-connector-java-5.1.25 /mysql-connector-java-5.1.25-bin.jar
2. 如果重要的话，我可以使用“mysql -uroot -ptcial addressBook”连接到 mysql。
3. 也尝试使用“-cp”参数运行，但无济于事。
4. 我可以让我的#3 DbConnect.java 类说“已建立数据库连接”。
5. 此外#4 DbQueryWorking.java 没有问题并提供预期的输出。

你能帮我理解这里有什么问题吗？

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, userName, 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);
}

}
}

Answer 1

看起来里面的网址DbConnector.java是错误的。缺少一个冒号。网址必须是：

jdbc:mysql://localhost:3306/

并不是

jdbc:mysql//localhost:3306/

Answer 2

你的网址是错误的，你缺少一个冒号，它应该是：

String url = "jdbc:mysql://localhost:3306/";