JAVA WEB篇2——Servlet

Servlet（Server Applet）是Java Servlet的簡(jiǎn)稱(chēng)，稱(chēng)為小服務(wù)程序或服務(wù)連接器，是Java語(yǔ)言編寫(xiě) 的服務(wù)器端程序，換句話(huà)說(shuō)，Servlet就是運(yùn)行在服務(wù)器上的Java類(lèi)。 Servlet用來(lái)完成B/S架構(gòu)下客戶(hù)端請(qǐng)求的響應(yīng)處理，也就是交互式地瀏覽和生成數(shù)據(jù)，生成動(dòng)態(tài)Web內(nèi)容

1、第一個(gè)servlet程序（servlet）

導(dǎo)入依賴(lài)

<!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api --><dependency><groupId>javax.servlet</groupId><artifactId>javax.servlet-api</artifactId><version>4.0.0</version><scope>provided</scope></dependency>

1.1、實(shí)現(xiàn)Servlet

public class HelloServlet implements Servlet {@Overridepublic void init(ServletConfig servletConfig) throws ServletException {System.out.println("servlet初始化");}@Overridepublic ServletConfig getServletConfig() {return null;}@Overridepublic void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {System.out.println("servlet被訪(fǎng)問(wèn)了");}@Overridepublic String getServletInfo() {return null;}@Overridepublic void destroy() {System.out.println("servlet銷(xiāo)毀");} } <?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"><servlet><servlet-name>hello</servlet-name><servlet-class>HelloServlet</servlet-class></servlet><servlet-mapping><servlet-name>hello</servlet-name><url-pattern>/hello</url-pattern></servlet-mapping> </web-app>

1.2、繼承GenericServlet

public class HelloServlet extends GenericServlet {@Overridepublic void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {System.out.println("servlet被訪(fǎng)問(wèn)了");} }

1.3、繼承HttpServlet

public class HelloServlet extends HttpServlet {@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("servlet被訪(fǎng)問(wèn)了");} }

1.4、Servlet注解

@WebServlet("/RuoyrServlet") public class RuoyrServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("post");}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("get");} }

2、Servlet的生命周期

創(chuàng)建（init）: 用戶(hù)第一次訪(fǎng)問(wèn)servlet創(chuàng)建servlet的實(shí)例.

銷(xiāo)毀（destroy）: 當(dāng)項(xiàng)目從服務(wù)器移除,或服務(wù)器關(guān)閉的時(shí)候

3、請(qǐng)求參數(shù)的獲取

方法聲明功能介紹

String getParameter(String name)	以字符串形式返回請(qǐng)求參數(shù)的值，如果該參數(shù)不存在，則返回空值
String[] getParameterValues( String name)	返回一個(gè)字符串對(duì)象數(shù)組，其中包含給定請(qǐng)求參數(shù)所具有的所有 值，如果該參數(shù)不存在，則返回空值
Enumeration getParameterNames()	返回包含此請(qǐng)求中包含的參數(shù)名稱(chēng)的字符串對(duì)象的枚舉。如果請(qǐng) 求沒(méi)有參數(shù)，則方法返回空枚舉
Map getParameterMap()	返回請(qǐng)求參數(shù)的鍵值對(duì)，一個(gè)鍵可以對(duì)應(yīng)多個(gè)值
String getRemoteAddr()	返回發(fā)送請(qǐng)求的客戶(hù)端或最后一個(gè)代理的IP地址
int getRemotePort()	返回發(fā)送請(qǐng)求的客戶(hù)端或最后一個(gè)代理的端口號(hào)
String getRequestURI()	返回此請(qǐng)求的資源路徑信息
StringBuffer getRequestURL()	返回此請(qǐng)求的完整路徑信息
String getMethod()	返回發(fā)出此請(qǐng)求的HTTP方法的名稱(chēng)，例如GET、POST
String getQueryString()	返回路徑后面請(qǐng)求中附帶的參數(shù)
String getServletPath()	返回此請(qǐng)求中調(diào)用servlet的路徑部分

4、響應(yīng)消息

@WebServlet("/RuoyrServlet") public class RuoyrServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("post");}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("get");response.setCharacterEncoding("UTF8");response.setContentType("text/html;charset=utf-8");PrintWriter writer = response.getWriter();writer.write("我已收到請(qǐng)求");} }

5、請(qǐng)求亂碼處理

public class RuoyrServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("post");System.out.println(request.getParameter("name"));System.out.println(new String(request.getParameter("name").getBytes("ISO-8859-1"),"UTF8"));response.setCharacterEncoding("UTF8");response.setContentType("text/html;charset=utf-8");PrintWriter writer = response.getWriter();writer.write("我已收到請(qǐng)求");}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("get");} }

6、ServletConfig、ServletContext

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"><servlet><servlet-name>hello</servlet-name><servlet-class>HelloServlet</servlet-class><init-param><param-name>usernaame</param-name><param-value>admin</param-value></init-param></servlet><servlet-mapping><servlet-name>hello</servlet-name><url-pattern>/hello</url-pattern></servlet-mapping><context-param><param-name>username</param-name><param-value>ruoye</param-value></context-param> </web-app> public class HelloServlet implements Servlet {@Overridepublic void init(ServletConfig servletConfig) throws ServletException {System.out.println(servletConfig.getServletName());System.out.println(servletConfig.getInitParameter("username"));ServletContext servletContext = servletConfig.getServletContext();Enumeration<String> attributeNames = servletContext.getAttributeNames();while (attributeNames.hasMoreElements()){System.out.println(attributeNames.nextElement());}}@Overridepublic ServletConfig getServletConfig() {return null;}@Overridepublic void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {}@Overridepublic String getServletInfo() {return null;}@Overridepublic void destroy() {} }

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