java JDBC自我总结

preparedstatement和statement的区别

当不需要预编译时（不需要占位符）可以选用statement,存在不安全

当有占位符（？）时，需要选用preparedstatement

select 查询语句，选用executeQuery（）方法

执行后返回代表查询结果的ResultSet对象

ResultSet rs =pst.executeQuery("select * from teacher");

while (rs.next()){

System.out.println(rs.getInt(1) + "/t" +    rs.getString(2));

}

 INSERT、UPDATE 或 DELETE 语句以及 SQL DDL（数据定义语言）语句，例如 CREATE TABLE 和 DROP TABLE。选用executeUpdate（）方法

executeUpdate 的返回值是一个整数（int），指示受影响的行数（即更新计数）。
对于 CREATE TABLE 或 DROP TABLE 等不操作行的语句，executeUpdate 的返回值总为零

insert实例

private static int insert(Student student) {
    Connection conn = getConn();
    int i = 0;
    String sql = "insert into students (Name,Sex,Age) values(?,?,?)";
    PreparedStatement pstmt;
    try {
        pstmt = (PreparedStatement) conn.prepareStatement(sql);
        pstmt.setString(1, student.getName());
        pstmt.setString(2, student.getSex());
        pstmt.setString(3, student.getAge());
        i = pstmt.executeUpdate();
        pstmt.close();
        conn.close();
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return i;
}

查询样例

private static Integer getAll() {
    Connection conn = getConn();
    String sql = "select * from students";
    PreparedStatement pstmt;
    try {
        pstmt = (PreparedStatement)conn.prepareStatement(sql);
        ResultSet rs = pstmt.executeQuery();
        int col = rs.getMetaData().getColumnCount();
        System.out.println("============================");
        while (rs.next()) {
            for (int i = 1; i <= col; i++) {
                System.out.print(rs.getString(i) + "\t");
                if ((i == 2) && (rs.getString(i).length() < 8)) {
                    System.out.print("\t");
                }
             }
            System.out.println("");
        }
            System.out.println("============================");
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return null;
}