servlet初体验

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使用servlet规范来编写一个应用

1、继承HttpServlet抽象类就可以了

@WebServlet("/hel")public class MyServlet extends HttpServlet {    @Override    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {        System.out.println("请求到达Servlet了");        System.out.println("响应从Servlet返回了");    }    @Override    public void init() throws ServletException {        System.out.println("Servlet初始化");    }    @Override    public void destroy() {        System.out.println("Servlet被销毁");    }}

2、servlet规范还提供了了filter组件

@WebFilter("/hel")public class MyFilter implements Filter {    public void init(FilterConfig filterConfig) throws ServletException {        System.out.println("过滤器初始化");    }    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {        System.out.println("请求到达过滤器了");        filterChain.doFilter(servletRequest, servletResponse);    }    public void destroy() {        System.out.println("过滤器销毁");    }}

@WebFilter("/hel")public class MyFilter2 implements Filter {    public void init(FilterConfig filterConfig) throws ServletException {        System.out.println("过滤器2初始化");    }    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {        System.out.println("请求到达过滤器2了");        filterChain.doFilter(servletRequest, servletResponse);    }    public void destroy() {        System.out.println("过滤器2销毁");    }}

3、把这个应用放入servlet容器，比如tomcat，启动后控制台打印

过滤器2初始化
过滤器初始化

4、访问"/hel"，控制台打印

Servlet初始化
请求到达过滤器了
请求到达过滤器2了
请求到达Servlet了
响应从Servlet返回了

5、从打印可以看出servlet和filter的初始化顺序，调用顺序，如果想要深入的了解servlet，就要去看tomcat了。

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