Java 建立mysql数据库连接的语句

每次在面试时被问到jdbc的数据路链接过程都卡着，这次不怕了，背会了。。。
第一个 ，比较粗糙的
try{  
Class.forName("com.mysql.jdbc.Driver");
}
catch(ClassNotFoundException e) {}
//定义所要用到的三个数据库应用对象
Connection con=null; //连接对象
Statement sql=null; //Statement对象（SQL语句）
ResultSet rs=null; //结果集对象
//进行数据源的连接
try{  
con=DriverManager.getConnection ("jdbc:mysql://localhost/scutcs","","");//连接数据库的url 用户名和密码
sql=con.createStatement();
String to="Select * From user1 Where username='"+username+"'";
rs=sql.executeQuery(to); //根据所定义的Statement执行生成相应的结果集并存在RS中
if(rs.next()) //判断结果集是否为空，如果不为空则表示有记录
{
out.print("<script>alert('用户名 "+xm+"已存在，请另选一个!');history.back();</script>");//如果存在返回注册页面
}
else {如果不存在就向数据库添加一条记录}
}
catch (SQLException e)  
{ out.print(e);  
}

第二个 ，作为公共类比较完整些的  把部分的定义为单个函数方便调用
import java.sql.*;

public class DB {
public static Connection getConn() {
Connection conn = null;
try {
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:mysql://localhost/shopping?user=root&password=123456");
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}

return conn;
}

public static PreparedStatement prepare(Connection conn, String sql) {
PreparedStatement pstmt = null;  
try {
if(conn != null) {
pstmt = conn.prepareStatement(sql);
}
} catch (SQLException e) {
e.printStackTrace();
}
return pstmt;
}

public static PreparedStatement prepare(Connection conn, String sql, int autoGenereatedKeys) {
PreparedStatement pstmt = null;  
try {
if(conn != null) {
pstmt = conn.prepareStatement(sql, autoGenereatedKeys);
}
} catch (SQLException e) {
e.printStackTrace();
}
return pstmt;
}

public static Statement getStatement(Connection conn) {
Statement stmt = null;  
try {
if(conn != null) {
stmt = conn.createStatement();
}
} catch (SQLException e) {
e.printStackTrace();
}
return stmt;
}

/*
public static ResultSet getResultSet(Connection conn, String sql) {
Statement stmt = getStatement(conn);
ResultSet rs = getResultSet(stmt, sql);
close(stmt);
return rs;
}
*/

public static ResultSet getResultSet(Statement stmt, String sql) {
ResultSet rs = null;
try {
if(stmt != null) {
rs = stmt.executeQuery(sql);
}
} catch (SQLException e) {
e.printStackTrace();
}
return rs;
}

public static void executeUpdate(Statement stmt, String sql) {
try {
if(stmt != null) {
stmt.executeUpdate(sql);
}
} catch (SQLException e) {
e.printStackTrace();
}
}

public static void close(Connection conn) {
try {
if(conn != null) {
conn.close();
conn = null;
}
} catch (SQLException e) {
e.printStackTrace();
}
}

public static void close(Statement stmt) {
try {
if(stmt != null) {
stmt.close();
stmt = null;
}
} catch (SQLException e) {
e.printStackTrace();
}
}