day29 java和mysql

1.java中提供接口为多种数据库提供规范

• 具体实现接口类由各数据厂商提供

2.开发步骤

1.注册驱动.2.获得连接.
3.获得语句执行平台4.执行sql语句
5.处理结果6.释放资源.
---------------------
不使用java.sql.DriverManager.registerDriver(new Driver());
是因为registerDriver同样有new会注册两次
Class.forName("com.mysql.jdbc.Driver");
String urlString=
"jdbc:mysql://localhost:3306/myabc",
 usename = "root",
 password = "0616"; 
Connection co = DriverManager.getConnection(urlString, usename,password);
String sql = "SELECT * FROM datausers ";
        Statement st = co.createStatement();
        ResultSet rest = st.executeQuery(sql);
        List arr=new ArrayList();
        while (rest.next()) {
Datausers use=new Datausers(rest.getString("dser"), rest.getString("dpassword"));
            arr.add(use);
        }
        co.close();
    st.close();
    rest.close();
使用Statement 会产生注入攻击密码后加入'or'1=1就会为真
-----------------------使用PreparedStatement 不会产生注入攻击并且速度快
public static void main(String[] args) throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
String urlString = "jdbc:mysql://localhost:3306/myabc", usename = "root", password = "0616";
        Connection co = DriverManager.getConnection(urlString, usename,
                password);
        String sql = "SELECT * FROM datausers WHERE dser=?AND dpassword=?or 1=1";
        PreparedStatement ps = co.prepareStatement(sql);
        Scanner sc = new Scanner(System.in);
        String user = sc.nextLine();
        String pass = sc.nextLine();

        ps.setObject(1, user);
        ps.setObject(2, pass);
        ResultSet rest = ps.executeQuery();上处使用sql已经初始化此处就不用了
        while (rest.next()) {
System.out.println(rest.getObject("dser") + "  "
                    + rest.getObject("dpassword"));

        }
        rest.close();
        ps.close();
        co.close();
}
executeQuery()返回ResultSet可以处理结果
而st.executeUpdate()会返回int仅可以做insert，delete，update

3.注册，close重复代码多，写成tool类

public class Propertool {
    private static Connection co;
    static {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String urlString = "jdbc:mysql://localhost:3306/myabc", usename = "root", password = "0616";
co = DriverManager.getConnection(urlString, usename, password);
} catch (Exception ex) {
            throw new RuntimeException(ex + "连接数据库失败");
        }
    }
private Propertool() {
    }
    public static Connection getConnection() {
        return co;
    }
    public static void close(Connection co, Statement st, ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
        } catch (Exception e) { }
        }
        if (co != null) {
            try {
                co.close();
            } catch (Exception e) {
            }
        }
        if (st != null) {
            try {
                st.close();
            } catch (Exception e) {
                // TODO: handle exception
            }
        }
    }

4.将url等写成曾配置文件

• newfile文件，注意空格问题（可能在句末）
• 文件放在src下，如此会在创建时同样在bin目录下创建（bin是放编译后class文件地方）

drivername=com.mysql.jdbc.Driver
urlString=jdbc:mysql://localhost:3306/myabc
usename=root
password=0616
---------------------------用Properties读取
public class sqlBin {
public static void main(String[] args) throws Exception{
InputStream in= sqlBin.class.getClassLoader().getResourceAsStream("databases.properties");
Properties pro=new Properties();
pro.load(in);
String drivername= pro.getProperty("drivername");
String urlString= pro.getProperty("urlString");
String usename=pro.getProperty("usename");
String password=pro.getProperty("password");
System.out.println(drivername+ "  "+password+" "+urlString  +"  "+usename);
Class.forName(drivername);
Connection con=DriverManager.getConnection(urlString, usename, password);
System.out.println(con);
con.close();
}}
在使用java连接时候需要打开mysql服务（net start mysql）
-----------------------
实际使用时候需要将本类写成工具类，在代码块中static{}中调取方法
public class sqlBin {
private static String drivername;
private static String urlString;
private static String usename;
private static String password;
private static Connection con;
    
static
{
    try {
        getConfig();
        Class.forName(drivername);
         con=DriverManager.getConnection(urlString, usename, password);

    } catch (Exception e) {
throw new RuntimeException("连接数据库失败");  }
    }
private static void getConfig ()throws Exception
{
    InputStream in= sqlBin.class.getClassLoader().getResourceAsStream("databases.properties");
    Properties pro=new Properties();
    pro.load(in);
     drivername= pro.getProperty("drivername");
     urlString= pro.getProperty("urlString");
     usename=pro.getProperty("usename");
     password=pro.getProperty("password");
    
}