public class OkServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //可以写自己的业务处理代码
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //可以写自己的业务处理代码
    }

快速入门

省去了在web.xml配置的麻烦

方法外不能使用.var

/**
 * 显示方法之间的分割线 Editor->General->Appearance->Show method separators
 * 1.@WebServlet是一个注解
 * 2.@WebServlet的源码
 * 3.urlPatterns 对应web.xml中的 <url-Pattern></url-Pattern>
 *   {"/ok1", "/ok2"} 可以给OkServlet配置多个 urlPattern
 *   相当于这个@WebServlet(urlPatterns={"/ok1", "/ok2"}) 代替了web.xml的配置
 * 4.浏览器可以这样访问OkServlet: http://localhost:8080/servlet/ok1 或者 http://localhost:8080/servlet/ok2
 */
@WebServlet(urlPatterns = {"/ok1", "/ok2"})
public class OkServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("annotation doGet method");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("annotation doPost method");
    }
}

@WebServlet注解源码

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented => 在javadoc工具生成记录
public @interface WebServlet {
    String name() default "";

    String[] value() default {};

    String[] urlPatterns() default {};

    int loadOnStartup() default -1;

    WebInitParam[] initParams() default {};

    boolean asyncSupported() default false;

    String smallIcon() default "";

    String largeIcon() default "";

    String description() default "";

    String displayName() default "";
}

注解详解

说明: 注解是对包进行扫描, 如果发现某个类是用@WebServlet, 就说明该类是Servlet, 然后读取urlPatterns, 看看请求的资源和urlPatterns的参数是否一致

●模拟代码

/**
 * @author 赵志伟
 * @version 1.0
 * 模拟Tomcat是如何通过注解@WebServlet(urlPatterns={"/ok1", "/ok2"})来装载一个Servlet的
 */
@SuppressWarnings({"all"})
public class TestAnnotationServlet {

    private static final HashMap<String, HttpServlet> hm = new HashMap<>();
    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        //1.首先要得到扫描的包 路径 IO, 进而得到类的全路径
        String path = "com.zzw.servlet.annotation.OkServlet";
        //2.得到OkServlet的Class对象
        Class<?> aClass = Class.forName(path);
        //3.根据class对象得到对应的注解
        WebServlet annotation = aClass.getAnnotation(WebServlet.class);
        String[] urlPatterns = annotation.urlPatterns();
        for (String urlPattern : urlPatterns) {
            System.out.println("urlPattern=" + urlPattern);
        }
        //如果匹配url, 如果是第一次, tomcat就会创建一个OkServlet实例, 放入到HashMap中
        Object instance = aClass.newInstance();
        System.out.println("instance=" + instance);//OkServlet实例

        hm.put("OkServlet", (HttpServlet) instance);
        System.out.println(hm);
    }
}

initParams

@WebServlet(urlPatterns = {"/ok1", "/ok2"}, initParams = {@WebInitParam(name = "zzw", value = "123"), @WebInitParam(name = "xx", value = "yy")})
public class OkServlet extends HttpServlet {}

等同于

<servlet>
        <servlet-name>OkServlet</servlet-name>
        <servlet-class>com.zzw.servlet.OkServlet</servlet-class>

        <init-param>
            <param-name>zzw</param-name>
            <param-value>123</param-value>
        </init-param>
        <init-param>
            <param-name>xx</param-name>
            <param-value>yy</param-value>
        </init-param>
    </servlet>

Servlet urlPattern 配置

精准匹配

@WebServlet(urlPatterns = {"/ok1/aa/bb", "/ok2"}

目录匹配

@WebServlet(urlPatterns = {"/ok1/*", "/ok2"})
http://localhost:8888/servlet/ok1
http://localhost:8888/servlet/ok1/aa
http://localhost:8888/servlet/ok1/aa/bb/cc

扩展名匹配

@WebServlet(urlPatterns = {"*.action", "/ok2"}
http://localhost:8888/servlet/zzw.action
http://localhost:8888/servlet/zzw.521.action

3.2不能带斜杠

@WebServlet(urlPatterns = {"/*.action", "/ok2"},这样是错误的

任意匹配

@WebServlet(urlPatterns = {"/", "/ok2"}
或者
@WebServlet(urlPatterns = {"/*", "/ok2"}
http://localhost:8888/servlet/aa/bb/cc
http://localhost:8888/servlet/zzw.521.action

注解注意事项

shortcuts: ctrl+alt+⬅ 回到上次访问的窗口

1.当Servlet配置了"/", 会覆盖掉tomcat的DefaultServlet, 当其它的的url-pattern都匹配不上时, 就会走这个默认的Servlet, 这样可以拦截到其它请求中的静态资源

这个默认的Servlet是处理静态资源的, 一旦拦截, 静态资源则不能处理

 <!-- The default servlet for all web applications, that serves static     -->
  <!-- resources.  It processes all requests that are not mapped to other   -->
  <!-- servlets with servlet mappings (defined either here or in your own   -->
  <!-- web.xml file). -->
	<servlet>
        <servlet-name>default</servlet-name>
        <servlet-class>org.apache.catalina.servlets.DefaultServlet</servlet-class>
        <init-param>
            <param-name>debug</param-name>
            <param-value>0</param-value>
        </init-param>
        <init-param>
            <param-name>listings</param-name>
            <param-value>false</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

2.当Servlet配置了"/*", 表示可以匹配任意访问路径

3.建议不要使用/ 和 /*, 尽量使用精准匹配

4.优先级遵守: 精确路径 > 目录路径 > 扩展名路径 > /* > / > DefaultServlet(访问静态资源)

访问:http://localhost:8888/servlet/ok1/aa
@WebServlet(urlPatterns = {"/ok1/aa"}//优先
@WebServlet(urlPatterns = {"/ok1/*"}