Request 其他功能

一、獲取請求參數通用方式

不論get還是post請求方式都可以使用下列方法來獲取請求參數

（1）String getParameter(String name):根據參數名稱獲取參數值    
（2）String[] getParameterValues(String name):根據參數名稱獲取參數值的數組 
	類似：獲取複選框的值 hobby=xx&hobby=game
（3）Enumeration<String> getParameterNames():獲取所有請求的參數名稱
（4）Map<String,String[]> getParameterMap():獲取所有參數的map集合

@WebServlet("/requestDemo")
public class RequestDemo6 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //post 獲取請求參數

        //根據參數名稱獲取參數值
        String username = request.getParameter("username");
       /* System.out.println(username);*/

       //根據參數名稱獲取參數值的數組
        String[] hobbies = request.getParameterValues("hobby");
        /*for (String hobby : hobbies) {
            System.out.println(hobby);
        }*/

        //獲取所有請求的參數名稱
        Enumeration<String> parameterNames = request.getParameterNames();
        /*while(parameterNames.hasMoreElements()){
            String name = parameterNames.nextElement();
            System.out.println(name);
            String value = request.getParameter(name);
            System.out.println(value);
            System.out.println("----------------");
        }*/

        // 獲取所有參數的map集合
        Map<String, String[]> parameterMap = request.getParameterMap();
        //遍歷
        Set<String> keyset = parameterMap.keySet();
        for (String name : keyset) {
            //獲取鍵獲取值
            String[] values = parameterMap.get(name);
            System.out.println(name);
            for (String value : values) {
                System.out.println(value);
            }
        }


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //get 獲取請求參數
/*
        //由於獲取請求方式是通用的，所以這裏如果是Get方式,可以直接跳轉到 Post 執行
        this.doPost(request,response);
    }
}

* 中文亂碼問題：
	* get方式：tomcat 8 已經將get方式亂碼問題解決了
	* post方式：會亂碼
	* 解決：在獲取參數前，設置request的編碼request.setCharacterEncoding("utf-8");

@WebServlet("/requestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        System.out.println(username);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

解決：

@WebServlet("/requestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //設置流的編碼
        request.setCharacterEncoding("utf-8");
        String username = request.getParameter("username");
        System.out.println(username);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

二、 請求轉發

一種在服務器內部的資源跳轉方式

1. 步驟：
	（1）通過request對象獲取請求轉發器對象：RequestDispatcher getRequestDispatcher(String path)
	（2） 使用RequestDispatcher對象來進行轉發：forward(ServletRequest request, ServletResponse response) 

@WebServlet("/requestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.print("requestDemo 被訪問了。。。");
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/servletDemo");
        requestDispatcher.forward(request,response);

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

2. 特點：
	（1）瀏覽器地址欄路徑不發生變化
	（2）只能轉發到當前服務器內部資源中如同這裏 servletDemo 和 requestDemo在同一個Tomcat服務器內
	（3）轉發是一次性請求,使用抓包工具可以發現，只轉發了一次請求

三、 共享數據：

* 域對象：一個有作用範圍的對象，可以在範圍內共享數據
* request域：代表一次請求的範圍，一般用於請求轉發的多個資源中共享數據
* 方法：
	（1）void setAttribute(String name,Object obj):存儲數據
	（2）Object getAttitude(String name):通過鍵獲取值
	（3）void removeAttribute(String name):通過鍵移除鍵值對

@WebServlet("/requestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("requestDemo 被訪問了。。。");

//        存儲數據到 request 域中
        request.setAttribute("msg", "hello");
        //進行轉發
        request.getRequestDispatcher("/servletDemo").forward(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

四、獲取 ServletContext

ServletContext getServletContext()

@WebServlet("/requestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = request.getServletContext();
        System.out.println(servletContext);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}