小例子 使用反射机制创建dao的factory
public class Factory {
private static Properties props =
new Properties();
static{
InputStream
ips =
Factory.class.getClassLoader()
.getResourceAsStream(
"util/dao.properties");
try
{
props.load(ips);
} catch (IOException e)
{
e.printStackTrace();
}
}
public
static Object getInstance(String type){
Object obj =
null;
//依据接口名称(type)找到类名
String className =
props.getProperty(type);
try
{
Class c =
Class.forName(className);
//依据方法区中的class对象，创建
//一个实例。
obj
= c.newInstance();
} catch (Exception e)
{
e.printStackTrace();
}
return
obj;
}
}
在web中调用到就可以比较方便，例如：
public class ActionServlet extends HttpServlet {
public void service(HttpServletRequest request, HttpServletResponse
response)
throws ServletException, IOException
{
request.setCharacterEncoding("utf-8");
String
uri = request.getRequestURI();
String action =
uri.substring(uri.lastIndexOf("/"),
uri.lastIndexOf("."));
if(action.equals("/login")){
String
username =
request.getParameter(
"username");
String
pwd = request.getParameter("pwd");
UserDAO dao
=
(UserDAO)Factory.getInstance("UserDAO");
try
{
User user =
dao.findByUsername(
username);
if(user
!= null &&
user.getPwd().equals(pwd)){
//登录成功,跳转到主功能页面
HttpSession
session =
request.getSession();
session.setAttribute("user",
user);
response.sendRedirect("main.jsp");
}else{
//登录失败,提示用户输入正确的用户名和密码
request.setAttribute("login_error",
"用户名或密码错误");
request.getRequestDispatcher("login.jsp")
.forward(request,
response);
}
} catch (Exception
e)
{
e.printStackTrace();
throw
new
ServletException(e);
}
}
}
}