Servlet的学习（一）——核心接口和类、创建方式、配置方式

一、核心接口和类

①Servlet接口

Servlet接口是ServletAPI中最重要的接口，所有Servlet都会直接或间接的与该接口发生联系，或是直接实现该接口，或间接继承自实现了该接口的类。

该接口包含以下五个方法：

init(ServletConfig config)

ServletConfig getServletConfig()

service(ServletRequest req,ServletResponse res)

String getServletInfo()

destroy( )

②GenericServlet抽象类

它对Servlet接口中的部分方法（init和destroy）添加了实现，使得开发时只需要考虑针对service方法的业务实现即可

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③HttpServlet类

是继承GenericServlet的基础上进一步的扩展

二Servlet创建的三种方式

①继承HttpServlet

public class HelloServlet extends HttpServlet {

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.getWriter().print("我是Servlet创建的第一种方式");
	}

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

②实现接口Servlet

public class HelloServlet2 implements Servlet {

	@Override
	public void destroy() {
	}

	@Override
	public ServletConfig getServletConfig() {
		return null;
	}

	@Override
	public String getServletInfo() {
		return null;
	}

	@Override
	public void init(ServletConfig arg0) throws ServletException {
	}

	@Override
	public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException {
		System.out.println("OK");
		response.setContentType("text/html;charset=UTF-8");
		response.getWriter().println("我是第二种创建方式");
	}
}

③继承·GenericServlet类

public class HelloServlet3 extends GenericServlet{

	@Override
	public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException {
		System.out.println("OK");
		response.setContentType("text/html;charset=UTF-8");
		response.getWriter().println("我是第三种创建方式");
	}
}

三、Servlet的两种配置方式

①注解式配置（Servlet3.0以后才行）

@WebServlet(value = "/hello", loadOnStartup = 1)
public class HelloServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.getWriter().print("OK");
	}

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

loadOnStartup是设置优先级别，如果有多个Servlet，需要设置，如果只有一个，可以不用设，只有一个可以直接在注解里面写上Servlet名字就行。

②web.xml配置（Servlet所有版本都支持）

public class HelloServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.getWriter().print("OK");
	}

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

<!--Servlet的第二种配置 -->
	<!--Servlet配置 -->
	<servlet>
		<!--名称 -->
		<servlet-name>hello2</servlet-name>
		<!--Servlet的全称类名 -->
		<servlet-class>com.qf.web.servlet.HelloServlet</servlet-class>
		<!--启动的优先级，数字越小越先起作用 -->
		<load-on-startup>1</load-on-startup>
	</servlet>
	<!--映射配置 -->
	<servlet-mapping>
		<!--名称 -->
		<servlet-name>hello2</servlet-name>
		<!--资源的匹配规则：精确匹配 -->
		<url-pattern>/hello2.do</url-pattern>
	</servlet-mapping>