第四天(HttpServlet类)

HttpServlet继承GenericServlet，针对于HTTP协议所定制

在service()方法中直接把ServletRequest和ServletResponse转为HttpServletRequest和HttpServletResponse，并调用了重载的 service(HttpServletRequest,HttpServletResponse)

在service(HttpServletRequest,HttpServletResponse)获取了请求方式：request.getMethod() 根据请求方式创建了doGet，doPost

实际开发中，直接继承HttpServlet，并根据请求方式复写doXxx()方法接口

public class LoginServlet extends HttpServlet {

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//获取请求方式是GET还是POST
		String method = request.getMethod();
		System.out.println(method);
		}
}

访问数据库例子

public class LoginServlet extends HttpServlet {

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		String username = request.getParameter("username");
		String password = request.getParameter("password");
		String sql = "SELECT count(id) FROM users WHERE username = ? AND password = ?";
		
		Connection connection = null;
		PreparedStatement statement = null;
		ResultSet resultSet = null;
		
		PrintWriter out = response.getWriter();
		
			try {
				Class.forName("com.mysql.jdbc.Driver");
				String url = "jdbc:mysql:///dbtes";
				String user = "root";
				String password2 = "123456";
				connection = DriverManager.getConnection(url,user,password2);
				
				statement = connection.prepareStatement(sql);
				statement.setString(1, username);
				statement.setString(2, password);
				
				resultSet = statement.executeQuery();
				
				if(resultSet.next()){
					int count = resultSet.getInt(1);
					if(count > 0){
						out.print("Success");
					}else{
						out.print("Error");
					}
				}
			} catch (Exception e) {
				e.printStackTrace();
			} finally {
				try {
					if(resultSet != null){
					resultSet.close();
					}
				} catch (SQLException e) {
					e.printStackTrace();
				}
				try {
					if(statement != null){
					statement.close();
					}
				} catch (SQLException e) {
					e.printStackTrace();
				}
				try {
					if(connection != null){
					connection.close();
					}
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
			
	}

}