定義

　　請求包含是指將另一個Servlet的請求處理流程包含進來。
　　請求轉發是指將請求轉發給別的Servlet處理。

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實現

　　實現請求包含和請求轉發，可以使用HttpServletRequest的getRequestDispatcher()方法取得RequestDispatcher接口的實現對象實例，調用時傳入請求、響應對象即可。
　　取得RequestDispatcher還有兩個方式，通過ServletContext的getRequestDispatcher()或getNamedDispatcher()。

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demo

package com.test;import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.PrintWriter;@WebServlet({"/some.controller", "/world"}) public class Some extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {PrintWriter out = response.getWriter();out.println("Some do one...");RequestDispatcher dispatcher = request.getRequestDispatcher("other.view");// 請求包含 dispatcher.include(request, response);// 請求轉發// dispatcher.forward(request, response);out.println("Some do two...");} } Some.java package com.test;import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.util.Arrays;@WebServlet({"/other.view", "/view"}) public class Other extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.getWriter().println("Other do one...");} } Other.java

請求轉發 forward 的響應結果是：

　　Other do one...

請求包含 include 的響應結果是：

　　Some do one...
　　Other do one...
　　Some do two...

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區別

　　forward：目前的Servlet不能有任何響應確認，如果在目前的Servlet中通過響應對象設置了一些響應但未確認（響應緩沖區未滿或未調用任何清除方法），則所有響應設置會被忽略，如果已經有響應確認且調用了forward()方法，則會拋出IllegalStateException。

　　include：被包含的Servlet中任何對請求標頭的設置都會被忽略。但被包含的Servlet中可以使用getSession()方法取得HttpSession對象。

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相同點

1、在取得RequestDispatcher時，也可以包括查詢字符串。
　　例如：req.getRequestDispatcher("other.view?data=123456").include(req, resp);
　　這樣在被包含或轉發的Servlet中就可以使用getParameter（"data"）取得請求參數值。
2．查詢字符串的方式，僅適用于傳遞字符串值給另一個Servlet；如果有必須共享的“對象”，可以設置給請求對象成為屬性。
　　HttpServletRequest上與請求范圍屬性有關的幾個方法如下。
　　setAttribute()：指定名稱與對象設置屬性。
　　getAttribute()：指定名稱取得屬性。
　　getAttributeNames()：取得所有屬性名稱。
　　removeAttribute()：指定名稱移除屬性。

example:

package com.test;import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.PrintWriter;@WebServlet({"/some.controller", "/world"}) public class Some extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setAttribute("setAttr", new int[]{1, 2, 3});PrintWriter out = response.getWriter();out.println("Some do one...");RequestDispatcher dispatcher = request.getRequestDispatcher("other.view?data=123456");// 請求包含// dispatcher.include(request, response);// 請求轉發 dispatcher.forward(request, response);out.println("Some do two...");} } Some.java package com.test;import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.util.Arrays;@WebServlet({"/other.view", "/view"}) public class Other extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String data = request.getParameter("data");int[] getAttr = (int[])request.getAttribute("setAttr");response.getWriter().println("Other do one..." + " | "+ "include or forward parameter: " + data + " | " // 請求或轉發時攜帶的查詢參數+ "setAttrbute object: " + Arrays.toString(getAttr)); // 共享對象 } } Other.java

請求轉發?forward?的響應結果是：

　　Other do one... | include or forward parameter: 123456 | setAttrbute object: [1, 2, 3]

請求包含?include?的響應結果是：

　　Some do one...
　　Other do one... | include or forward parameter: 123456 | setAttrbute object: [1, 2, 3]
　　Some do two...

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相似點

請 求 包 含	javax.servlet. include.request_uri	javax.servlet. include.context_path	javax.servlet. include.servlet_path	javax.servlet. include.path_info	javax.servlet. include.query_string
請 求 轉 發	javax.servlet. forward.request_uri	javax.servlet. forward.context_path	javax.servlet. forward.servlet_path	javax.servlet. forward.path_info	javax.servlet. forward.query_string
表 示 上 一 個 Servlet 的	Request URI	Context path	Servlet path	Path info	取得RequestDispatcher時 給定的查詢參數

?

?如果被包含或轉發的Servlet還包含或轉發其他的Servlet，則這些屬性名稱的對應值也會被代換。

example:

package com.test;import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.PrintWriter;@WebServlet({"/some.controller", "/world"}) public class Some extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {PrintWriter out = response.getWriter();out.println("Some do one...");RequestDispatcher dispatcher = request.getRequestDispatcher("other.view?data=123456");// 請求包含 dispatcher.include(request, response);// 請求轉發// dispatcher.forward(request, response);out.println("Some do two...");} } Some.java package com.test;import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException;@WebServlet({"/other.view", "/view"}) public class Other extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String request_uri, context_path, servlet_path, path_info, query_string;// 默認的請求包含時的參數/*request_uri = (String)request.getAttribute("javax.servlet.include.request_uri");context_path = (String)request.getAttribute("javax.servlet.include.context_path");servlet_path = (String)request.getAttribute("javax.servlet.include.servlet_path");path_info = (String)request.getAttribute("javax.servlet.include.path_info");query_string = (String)request.getAttribute("javax.servlet.include.query_string");*/// 默認的請求轉發時的參數request_uri = (String)request.getAttribute("javax.servlet.forward.request_uri");context_path = (String)request.getAttribute("javax.servlet.forward.context_path");servlet_path = (String)request.getAttribute("javax.servlet.forward.servlet_path");path_info = (String)request.getAttribute("javax.servlet.forward.path_info");query_string = (String)request.getAttribute("javax.servlet.forward.query_string");response.getWriter().println("Other do one..." + " | "+ "request_uri: " + request_uri + " | "+ "context_path: " + context_path + " | "+ "servlet_path: " + servlet_path + " | "+ "path_info: " + path_info + " | "+ "query_string: " + query_string);} } Other.java

請求轉發?forward?的響應結果是：

　　Other do one... | request_uri: /hello/some.controller | context_path: /hello | servlet_path: /some.controller | path_info: null | query_string: null

請求包含?include?的響應結果是：

　　Some do one...
　　Other do one... | request_uri: /hello/other.view | context_path: /hello | servlet_path: /other.view | path_info: null | query_string: data=123456
　　Some do two...

轉載于:https://www.cnblogs.com/Mike_Chang/p/10033063.html

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