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Java Web学习总结（3）Servlet（二）

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一，Servlet訪問URL映射配置

由于客戶端是通過URL地址訪問web服務(wù)器中的資源，所以Servlet程序若想被外界訪問，必須把servlet程序映射到一個URL地址上，這個工作在web.xml文件中使用<servlet>元素和<servlet-mapping>元素完成。

Servlet：該元素用于注冊Servlet，它包含有兩個主要的子元素：<servlet-name>和<servlet-class>，分別用于設(shè)置Servlet的注冊名稱和Servlet的完整類名。

servlet-mapping：該元素用于映射一個已注冊的Servlet的一個對外訪問路徑，它包含有兩個子元素：<servlet-name>和<url-pattern>，分別用于指定Servlet的注冊名稱和Servlet的對外訪問路徑。

同一個Servlet可以被映射到多個URL上，即多個<servlet-mapping>元素的<servlet-name>子元素的設(shè)置值可以是同一個Servlet的注冊名

<servlet><servlet-name>HelloServlet</servlet-name><servlet-class>com.zender.servlet.HelloServlet</servlet-class> </servlet> <servlet-mapping><servlet-name>HelloServlet</servlet-name><url-pattern>/hello.html</url-pattern> </servlet-mapping> <servlet-mapping><servlet-name>HelloServlet</servlet-name><url-pattern>/hello1.html</url-pattern> </servlet-mapping> <servlet-mapping><servlet-name>HelloServlet</servlet-name><url-pattern>/hello2.html</url-pattern> </servlet-mapping>

二，ServletURL通配符：*

在Servlet映射到的URL中也可以使用*通配符，但是只能有兩種固定的格式：

格式一：*.擴展名"

格式二：以正斜杠（/）開頭并以"/*"結(jié)尾

三，缺省Servlet

Servlet的映射路徑僅僅為一個正斜杠（/），那么這個Servlet就成為當(dāng)前Web應(yīng)用程序的缺省Servlet。凡是在web.xml文件中找不到匹配的<servlet-mapping>元素的URL，它們的訪問請求都將交給缺省Servlet處理。

四，ServletConfig

ServletConfig代表當(dāng)前Servlet在web.xml中的配置信息。

1，Servlet初始化參數(shù)

在Servlet的配置文件中，可以使用一個或多個<init-param>標(biāo)簽為servlet配置一些初始化參數(shù)。

例如：

<servlet><servlet-name>HelloServlet</servlet-name><servlet-class>com.zender.servlet.HelloServlet</servlet-class><init-param><param-name>name</param-name><param-value>Zender</param-value></init-param><init-param><param-name>encode</param-name><param-value>UTF-8</param-value></init-param> </servlet> <servlet-mapping><servlet-name>HelloServlet</servlet-name><url-pattern>/hello.html</url-pattern> </servlet-mapping>

2，通過ServletConfig獲取Servlet的初始化參數(shù)

當(dāng)servlet配置了初始化參數(shù)后，web容器在創(chuàng)建servlet實例對象時，會自動將這些初始化參數(shù)封裝到ServletConfig對象中，并在調(diào)用servlet的init方法時，將ServletConfig對象傳遞給servlet。進而，通過ServletConfig對象就可以得到當(dāng)前servlet的初始化參數(shù)信息。

public class HelloServlet extends HttpServlet{private static final long serialVersionUID = 3903946972744326948L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//獲取ServletConfigServletConfig config = this.getServletConfig();//獲取初始化參數(shù)String name = config.getInitParameter("name");String encode = config.getInitParameter("encode");//設(shè)置編碼格式，否則中文會出現(xiàn)亂碼resp.setCharacterEncoding("GBK");PrintWriter out = resp.getWriter();out.println("name:" + name);out.println("encode:" + encode);} }

五，ServletContext

WEB容器在啟動時，它會為每個WEB應(yīng)用程序都創(chuàng)建一個對應(yīng)的ServletContext對象，它代表當(dāng)前web應(yīng)用。

ServletConfig對象中維護了ServletContext對象的引用，開發(fā)人員在編寫servlet時，可以通過ServletConfig.getServletContext()方法獲得ServletContext對象。

由于一個WEB應(yīng)用中的所有Servlet共享同一個ServletContext對象，因此Servlet對象之間可以通過ServletContext對象來實現(xiàn)通訊。ServletContext對象通常也被稱之為context域?qū)ο蟆?

1，獲取WEB應(yīng)用的初始化參數(shù)

在web.xml文件中使用<context-param>標(biāo)簽配置WEB應(yīng)用的初始化參數(shù)：

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns="http://java.sun.com/xml/ns/javaee"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"id="WebApp_ID" version="3.0"><display-name>ServletDemo</display-name><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list><context-param><param-name>name</param-name><param-value>Zender</param-value></context-param><context-param><param-name>encode</param-name><param-value>UTF-8</param-value></context-param><servlet><servlet-name>HelloServlet</servlet-name><servlet-class>com.zender.servlet.HelloServlet</servlet-class></servlet><servlet-mapping><servlet-name>HelloServlet</servlet-name><url-pattern>/hello.html</url-pattern></servlet-mapping> </web-app>

獲取Web應(yīng)用的初始化參數(shù)：

public class HelloServlet extends HttpServlet{private static final long serialVersionUID = 3903946972744326948L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//獲取ServletContextServletContext context = this.getServletContext();//獲取初始化參數(shù)String name = context.getInitParameter("name");String encode = context.getInitParameter("encode");//設(shè)置編碼格式，否則中文會出現(xiàn)亂碼resp.setCharacterEncoding("GBK");PrintWriter out = resp.getWriter();out.println("name:" + name);out.println("encode:" + encode);} }

2，多個Servlet通過ServletContext對象實現(xiàn)數(shù)據(jù)共享

例如：ServletTwo獲得ServletOne所共享的數(shù)據(jù)

ServletOne：

public class ServletOne extends HttpServlet{private static final long serialVersionUID = 3903946972744326948L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//共享的數(shù)據(jù)String name = "zender";//獲取ServletContextServletContext context = this.getServletContext();//將name存儲到ServletContext對象中context.setAttribute("name", name);} }

ServletTwo：

public class ServletTwo extends HttpServlet{private static final long serialVersionUID = 3903946972744326948L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//獲取ServletContextServletContext context = this.getServletContext();//獲取初始化參數(shù)String name = (String) context.getAttribute("name");PrintWriter out = resp.getWriter();out.println("name:" + name);} }

Web.xml：

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns="http://java.sun.com/xml/ns/javaee"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"id="WebApp_ID" version="3.0"><display-name>ServletDemo</display-name><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list><servlet><servlet-name>ServletOne</servlet-name><servlet-class>com.zender.servlet.ServletOne</servlet-class></servlet><servlet-mapping><servlet-name>ServletOne</servlet-name><url-pattern>/ServletOne.html</url-pattern></servlet-mapping><servlet><servlet-name>ServletTwo</servlet-name><servlet-class>com.zender.servlet.ServletTwo</servlet-class></servlet><servlet-mapping><servlet-name>ServletTwo</servlet-name><url-pattern>/ServletTwo.html</url-pattern></servlet-mapping> </web-app>

先訪問：http://localhost:8081/ServletDemo/ServletOne.html

再訪問：http://localhost:8081/ServletDemo/ServletTwo.html

3，用servletContext實現(xiàn)請求轉(zhuǎn)發(fā)

context.getRequestDispatcher()方法實現(xiàn)請求轉(zhuǎn)發(fā)

ServletOne：

ServletTwo：

Web.xml：

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns="http://java.sun.com/xml/ns/javaee"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"id="WebApp_ID" version="3.0"><display-name>ServletDemo</display-name><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list><servlet><servlet-name>ServletOne</servlet-name><servlet-class>com.zender.servlet.ServletOne</servlet-class></servlet><servlet-mapping><servlet-name>ServletOne</servlet-name><url-pattern>/ServletOne.html</url-pattern></servlet-mapping><servlet><servlet-name>ServletTwo</servlet-name><servlet-class>com.zender.servlet.ServletTwo</servlet-class></servlet><servlet-mapping><servlet-name>ServletTwo</servlet-name><url-pattern>/ServletTwo.html</url-pattern></servlet-mapping> </web-app>

訪問：http://localhost:8081/ServletDemo/ServletOne.html

訪問的是ServletOne.html，瀏覽器顯示的卻是ServletTwo.html的內(nèi)容，這就是使用ServletContext實現(xiàn)了請求轉(zhuǎn)發(fā)。

4，利用ServletContext對象讀取資源文件

獲取上圖的config.properties資源文件內(nèi)容：

GetProperties.Java：

public class GetProperties extends HttpServlet{private static final long serialVersionUID = 3903946972744326948L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//設(shè)置瀏覽器編碼格式為UTF-8resp.setHeader("content-type","text/html;charset=UTF-8");resp.getWriter().println("讀取src目錄下的config.properties配置文件：");//讀取src目錄下的properties配置文件readProperties(resp,"/WEB-INF/classes/config.properties");resp.getWriter().println("<hr/>讀取WebRoot目錄下的config.properties配置文件：");//讀取WebRoot目錄下的properties配置文件readProperties(resp,"config.properties");}/*** * @方法名: readProperties* @描述: 獲取properties配置文件內(nèi)容* @param resp* @param fileUrl* @throws IOException * @創(chuàng)建人 zender*/protected void readProperties(HttpServletResponse resp, String fileUrl) throws IOException{//2種方式都能獲取到config.properties//InputStream in = new FileInputStream(this.getServletContext().getRealPath(fileUrl));InputStream in = this.getServletContext().getResourceAsStream(fileUrl);Properties prop = new Properties();prop.load(in);String url = prop.getProperty("database.url");String username = prop.getProperty("database.username");String password = prop.getProperty("database.password");resp.getWriter().println(MessageFormat.format("url={0},username={1},password={2}", url,username, password));} }

Web.xml：

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns="http://java.sun.com/xml/ns/javaee"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"id="WebApp_ID" version="3.0"><display-name>ServletDemo</display-name><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list><servlet><servlet-name>GetProperties</servlet-name><servlet-class>com.zender.servlet.GetProperties</servlet-class></servlet><servlet-mapping><servlet-name>GetProperties</servlet-name><url-pattern>/GetProperties.html</url-pattern></servlet-mapping> </web-app>

訪問路徑：http://localhost:8081/ServletDemo/GetProperties.html

轉(zhuǎn)載于:https://www.cnblogs.com/Zender/p/7598785.html

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