Servlet与JSP进阶

HTTP请求结构

• HTTP请求包含三部分：请求行，请求头，请求体
  

  巧用请求头开发多端应用

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    String userAgent=request.getHeader("User-Agent");
    response.setContentType("text/html;charset=utf-8");
    response.getWriter().println(userAgent);
    String output = "";
    if(userAgent.indexOf("Windows NT")!= -1) {
        output = "<h1>这是pc端首页</h1>";
    }else if (userAgent.indexOf("iPhone")!= -1) {
        output = "<h1>这是iPhone端首页</h1>";
    }else if (userAgent.indexOf("Android")!= -1) {
        output = "<h1>这是Android端首页</h1>";
    }
    response.getWriter().println(output);
}

响应结构

• HTTP响应包含三部分：响应行、响应头、响应体
  

ContentType的作用

• ContentType决定浏览器采用何种方式对响应体进行处理,决定了代码的展现形式

请求转发与重定向

请求转发

• 服务器会跳转，只会产生一次请求
• request.getRequestDispatcher).forward() -请求转发：不会改变地址栏中的地址
  

  响应重定向

• 浏览器端跳转，会产生两次请求
• response.sendRedirect() -响应重定向：回调转到重定向的地址
  

  设置请求自定义属性

• 请求允许创建自定义属性
• 设置请求属性: request.setAttribute(属性名， 属性值)
• 获取请求属性: Object attr = request.getAttribute(属性名)
  

  浏览前Cookie

• Cookie是浏览器保存在本地的文本内容
• Cookie常用于保存登录状态、用户资料等小文本
• Cookie具有时效性，Cookie内容会伴随请求发送给Tomcat

==================loginServlet=====================
@WebServlet("/cookies/login")
public class loginServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("用户登录成功!");
        Cookie cookie = new Cookie("user","admin");
        response.addCookie(cookie);     //创建Cookie信息
        cookie.setMaxAge(60*60*24*7);   //设置cookie的保存时间
        response.getWriter().println("login success!");
    }
}
===================indexServlect=======================
@WebServlet("/cookies/index")
public class indexServlect extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        Cookie[] cookie = request.getCookies();//获取Cookie信息
        if(cookie==null) {
            response.getWriter().println("user not login");
            return;
        }
        String user=null;
        for(Cookie cs : cookie) {
            String cd=cs.getName()+":"+cs.getValue();
            System.out.println(cd);
            response.getWriter().println(cd);
            if(cs.getName().equals("user")) {
                user=cs.getValue();
            }
        }
        if (user == null) {
            response.getWriter().println("user not login");
        }else {
            response.getWriter().println("user:"+user);
        }
    }
}

Session-用户会话

• Session (用户会话)用于保存与"浏览器窗口”对应的数据
• Session的数据存储在Tomcat服务器的内存中，具有时效性
• Session通过浏览器Cookie的Sessionld值提取用户数据
  与浏览器绑定的且吧内容存储在Tomcat中的对象

===========SessionLoginServlet=============
@WebServlet("/session/login")
public class SessionLoginServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("用户登录成功");
        //获取到用户会话Session对象
        HttpSession session = request.getSession();
        String sessionId = session.getId();
        System.out.println(sessionId);
        session.setAttribute("name", "admin");
        request.getRequestDispatcher("/session/index").forward(request, response);
    }
}
============SessionIndexServlet=================
@WebServlet("/session/index")
public class SessionIndexServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        String sessionId = session.getId();
        System.out.println(sessionId);
        String name = (String)session.getAttribute("name");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println("这是首页，当前用户为："+name);
    }
}

Session原理

ServletContext

• ServletContext(Servlet上下文对象),是Web应用全局对象
• 一个Web应用只会创建一个ServletContext对象
• ServletContext随着Web应用启动而自动创建

================ServletContextServlet===================
@WebServlet("/servletcontext/init")
public class ServletContextServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context = request.getServletContext();
        context.setAttribute("copyright", "afterglow");
        context.setAttribute("title", "唐僧洗头艹飘柔");
        response.getWriter().println("init success:");
    }
}
=================ServletContextDefaultServlet===================
@WebServlet("/servletcontext/default")
public class ServletContextDefaultServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletcontext = (ServletContext)request.getServletContext();
        String copyright = (String) servletcontext.getAttribute("copyright");
        String title = (String) servletcontext.getAttribute("title");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println("<h1>"+copyright+"</h1>");
        response.getWriter().println("<h1>"+title+"</h1>");
    }
}

Java Web三大作用域对象

• HttpServletRequest -请求对象：生命周期最短，当一个请求送往tomcat中，这个对象就会存在了，当Servlet处理完成并且产生响应返回给浏览器，当前的请求对象就会被销毁
• HttpSession -用户会话对象：第一次用户发来请求的时候创建，在30分钟后没有访问这个session就会被销毁
• ServletContext - web应用全局对象：Web应用程序启动的时候被创建，在Web应用程序重启或者关闭的时候被销毁
  作用域和生命周期依次递增
  能用小作用域开发的就不要使用大的作用域开发

Web应用的中文乱码由来

• Tomcat默认使用字符集ISO-8859-1,属于西欧字符集
• 解决乱码的核心思路是将ISO-8859-1转换为UTF-8
• Servlet中请求与响应都需要设置UTF-8字符集

@WebServlet("/charset/process")
public class CharsetServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //对于Tomcat8.x的版本，默认get请求发送中文就是UTF-8的格式，因此无需转换
        String ename = request.getParameter("ename");
        String address = request.getParameter("address");
        response.setContentType("text/html;charset=utf-8");//设置响应的输出字符集
        response.getWriter().println(ename+":"+address);
        System.out.println(ename+":"+address);
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //request.setCharacterEncoding方法用于将请求体重的字符集转为UTF-8
        request.setCharacterEncoding("UTF-8");
        // TODO Auto-generated method stub
        String ename = request.getParameter("ename");
        String address = request.getParameter("address");
        response.setContentType("text/html;charset=utf-8");//设置响应的输出字符集
        response.getWriter().println(ename+":"+address);
        System.out.println(ename+":"+address);
    }
}

web.xml常用配置

• 设置全局参数

• 获取url

================PatternServlet=====================
public class PatternServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //查询员工基本信息
        //获取当前访问的URL
        String url = request.getRequestURI().toString();
        System.out.println(url);
        String id = url.substring(url.lastIndexOf("/")+1);
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println(id);
    }
}
===================XML=======================
<servlet>
   <servlet-name>patternServlet</servlet-name>
   <servlet-class>fun.afterglow.servlet.pattern.PatternServlet</servlet-class>
</servlet>
<servlet-mapping>
   <servlet-name>patternServlet</servlet-name>
   <!--这里的url最后需要使用*-->
   <url-pattern>/pattern/*</url-pattern>
</servlet-mapping>

• 修改web应用默认首页

 <welcome-file-list>
   <welcome-file>index.html</welcome-file>
   <welcome-file>index.htm</welcome-file>
   <welcome-file>index.jsp</welcome-file>
   <welcome-file>default.html</welcome-file>
   <welcome-file>default.htm</welcome-file>
   <welcome-file>default.jsp</welcome-file>
 </welcome-file-list>
//web.xml会依次检查这些页面是否存在，如果有一个存在他就会自动加载

• Servlet通配符映射级初始化参数

==================XML======================
<context-param>
   <param-name>title</param-name>
   <param-value>唐僧洗头艹飘柔</param-value>
</context-param>
<context-param>
   <param-name>copyright</param-name>
   <param-value>afterglow</param-value>
</context-param>
=====================ServletContextServlet=========================
@WebServlet("/servletcontext/init")
public class ServletContextServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context = request.getServletContext();
        String copyright = context.getInitParameter("copyright");
        String title = context.getInitParameter("title");
        context.setAttribute("copyright", copyright);
        context.setAttribute("title", title);
        response.getWriter().println("init success:");
    }
}
===============ServletContextDefaultServlet=====================
@WebServlet("/servletcontext/default")
public class ServletContextDefaultServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletcontext = (ServletContext)request.getServletContext();
        String copyright = (String) servletcontext.getAttribute("copyright");
        String title = (String) servletcontext.getAttribute("title");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println("<h1>"+copyright+"</h1>");
        response.getWriter().println("<h1>"+title+"</h1>");
    }
}

• 设置404/500等状态码默认页面

 <!--指定错误页面 location需要指定页面所在位置-->
 <error-page>
   <error-code>404</error-code>
   <location>/error/404.html</location>
 </error-page>
 <error-page>
   <error-code>500</error-code>
   <location>/error/500.html</location>
 </error-page>

JSP九大内置对象

• 内置对象和在class中使用时完全一样的

<%
    String url = request.getRequestURL().toString();// HttpServletRequest
    response.getWriter().println(url);//HttpServletPrsponse
%>