每次在面試時被問到jdbc的數據路鏈接過程都卡著，這次不怕了，背會了。。。
第一個 ，比較粗糙的
try{ ?
Class.forName("com.mysql.jdbc.Driver");
}
catch(ClassNotFoundException e) {}
//定義所要用到的三個數據庫應用對象
Connection con=null; //連接對象
Statement sql=null; //Statement對象（SQL語句）
ResultSet rs=null; //結果集對象
//進行數據源的連接
try{ ?
con=DriverManager.getConnection ("jdbc:mysql://localhost/scutcs","","");//連接數據庫的url 用戶名和密碼
sql=con.createStatement();
String to="Select * From user1 Where username='"+username+"'";
rs=sql.executeQuery(to); //根據所定義的Statement執行生成相應的結果集并存在RS中
if(rs.next()) //判斷結果集是否為空，如果不為空則表示有記錄
{
out.print("<script>alert('用戶名 "+xm+"已存在，請另選一個!');history.back();</script>");//如果存在返回注冊頁面
}
else {如果不存在就向數據庫添加一條記錄}
}
catch (SQLException e) ?
{ out.print(e); ?
}

第二個 ，作為公共類比較完整些的? 把部分的定義為單個函數方便調用
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();
}
} ?