JAVA WEB篇2——Servlet

Servlet（Server Applet）是Java Servlet的簡稱，稱為小服務程序或服務連接器，是Java語言編寫 的服務器端程序，換句話說，Servlet就是運行在服務器上的Java類。 Servlet用來完成B/S架構下客戶端請求的響應處理，也就是交互式地瀏覽和生成數據，生成動態Web內容

1、第一個servlet程序（servlet）

導入依賴

<!-- 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、實現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被訪問了");}@Overridepublic String getServletInfo() {return null;}@Overridepublic void destroy() {System.out.println("servlet銷毀");} } <?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被訪問了");} }

1.3、繼承HttpServlet

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

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

創建（init）: 用戶第一次訪問servlet創建servlet的實例.

銷毀（destroy）: 當項目從服務器移除,或服務器關閉的時候

3、請求參數的獲取

方法聲明功能介紹

String getParameter(String name)	以字符串形式返回請求參數的值，如果該參數不存在，則返回空值
String[] getParameterValues( String name)	返回一個字符串對象數組，其中包含給定請求參數所具有的所有 值，如果該參數不存在，則返回空值
Enumeration getParameterNames()	返回包含此請求中包含的參數名稱的字符串對象的枚舉。如果請 求沒有參數，則方法返回空枚舉
Map getParameterMap()	返回請求參數的鍵值對，一個鍵可以對應多個值
String getRemoteAddr()	返回發送請求的客戶端或最后一個代理的IP地址
int getRemotePort()	返回發送請求的客戶端或最后一個代理的端口號
String getRequestURI()	返回此請求的資源路徑信息
StringBuffer getRequestURL()	返回此請求的完整路徑信息
String getMethod()	返回發出此請求的HTTP方法的名稱，例如GET、POST
String getQueryString()	返回路徑后面請求中附帶的參數
String getServletPath()	返回此請求中調用servlet的路徑部分

4、響應消息

@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("我已收到請求");} }

5、請求亂碼處理

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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