Servlet3 简单测试

1.注解定义servlet的时候如果 @WebServlet("some") 如果url-pattern前面不加 / 回报以下的错误，和web.xml中定义是一致的。

java.lang.IllegalArgumentException: Invalid [some] in servlet mapping

2.urlPatterns = {"/some" , "/aaa" , "/bbb"} 和 value= {"/some" , "/aaa" , "/bbb"} 的作用是一样的都是用来定义访问改Servlet的 url-pattern 但是只能用一个不能两个同事出现

3.如果同一个Servlet的类既在web.xml中定义又通过注解@WebServlet定义那么最终只会注册一个Servlet实例 url-pattern 为 web,xml的url-pattern 和注解中url-pattern 的并集

例如: web.xml 中 url-pattern为 /ccc @WebServlet中定义的 url-pattern 为 /aaa /bbb .那么该Servlet的最终 url-pattern 为 /aaa /bbb /ccc

4.如果web.xml中Servlet配置如下

 <servlet><servlet-name>Some-Servlet</servlet-name><servlet-class>com.fll.servletannotation.servlets.SomeServlet</servlet-class><init-param><param-name>address</param-name><param-value>北京</param-value></init-param>
</servlet><servlet-mapping><servlet-name>Some-Servlet</servlet-name><url-pattern>/ccc</url-pattern>
</servlet-mapping>

用注解配置如下

java">@WebServlet(urlPatterns = {"/some" , "/aaa" , "/bbb"} ,initParams = {@WebInitParam(name = "name" , value = "冯亮亮") , @WebInitParam(name = "age" , value = "20")})
public class SomeServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");PrintWriter writer = response.getWriter();writer.write("我是通过注解定义的Servlet3.0 <br>");Enumeration<String> initParameterNames = this.getInitParameterNames();while (initParameterNames.hasMoreElements()){String name = initParameterNames.nextElement();String value = this.getInitParameter(name);writer.write("name=" + name + " value=" + value + "<br>");}}
}

那么当通过 /some /aaa /bbb 访问是返回的是:
我是通过注解定义的Servlet3.0
name=name value=冯亮亮
name=age value=20

当通过 /ccc 访问的时候返回的是:
我是通过注解定义的Servlet3.0
name=address value=北京

4.如果同一个 Filter的类既在 web.xml url-pattern=/* 中定义了 Filter 又通过 @WebFilter("/*") 定义Filter那么相当于注册的两个独立的 Filter 实例。一个请求如果既符合 web.xml 中的url-pattern 又符合 @WebFilter("/*") 中的 url-pattern 那么这两个 Filter 都会被执行

5.如果同一个 Listener的类同时在 web.xml 和 @WebListener中定义 Listener 那么只会注册一个 Listener 实例

6. 当 web.xml 中的 metadata-complete="true" 时所有注解的配置都会失效 false时注解配置生效

<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/javaeehttp://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0" metadata-complete="true"></web-app>

7.上传文件

java">@MultipartConfig
@WebServlet("/upload")
public class UploadServlet extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {Part filePart = request.getPart("file");Collection<String> headers = filePart.getHeaderNames();for (String headerName : headers){String header = filePart.getHeader(headerName);System.out.println(headerName + "=================" + header);}//打印结果//content-disposition=================form-data; name="file"; filename="1501131329.png"//content-type=================image/png//获取该 part 的文件名String fileName = filePart.getSubmittedFileName();String realPath = this.getServletContext().getRealPath("/upload");String filePath = realPath + "/" + fileName;filePart.write(filePath);}
}

注意：（1）Servlet类上添加 @MultipartConfig
Annotation that may be specified on a {@link javax.servlet.Servlet} class, indicating that instances of the Servlet expect requests that conform to the multipart/form-data MIME type.

该注解的注释大概意思是: 该注解是被放在Servlet类上的，表明这个Servlet类的实例希望请求遵守 multipart/form-data MIME type.

8. Servlet异步
获取AsyncContext 对象的时候要用 AsyncContext asyncContext = request.startAsync();

千万不要使用AsyncContext asyncContext = request.getAsyncContext(); 这个方法是一个递归调用

如果该Servlet的属性 asyncSupported = false 的时候执行上面的语句回报以下的错误

the processing chain do not support async [com.fll.servletannotation.servlets.AsyncServlet]

java.lang.IllegalStateException: 当前链的筛选器或servlet不支持异步操作。

9.具体代码

java">/*** @author fll*/
@WebServlet(urlPatterns = "/async" , asyncSupported = true)
public class AsyncServlet extends HttpServlet {private static Logger logger = LoggerFactory.getLogger(AsyncServlet.class);@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("================================");response.setContentType("text/html;charset=UTF-8");final PrintWriter writer = response.getWriter();writer.write("主线程开始<br>");//AsyncContext asyncContext = request.getAsyncContext();final AsyncContext asyncContext = request.startAsync();asyncContext.addListener(new AsyncListener() {@Overridepublic void onComplete(AsyncEvent event) throws IOException {logger.info("=============================== onComplete");}@Overridepublic void onTimeout(AsyncEvent event) throws IOException {logger.info("=============================== onTimeout");}@Overridepublic void onError(AsyncEvent event) throws IOException {logger.info("=============================== onError");}@Overridepublic void onStartAsync(AsyncEvent event) throws IOException {logger.info("=============================== onStartAsync");}});//asyncContext.setTimeout(3000);asyncContext.start(new Runnable() {@Overridepublic void run() {for (int i = 0; i < 10; i++) {try {Thread.sleep(500);System.out.println("================ " + i);writer.write("================ " + i + "<br>");} catch (InterruptedException e) {e.printStackTrace();}}asyncContext.complete();//asyncContext.dispatch("show.jsp");//asyncContext.dispatch("show.jsp");等价于 request.getRequestDispatcher("show.jsp").include(request , response);同样有通知主线程子线程已经执行完毕的作用  也就是该方法也会将response中的数据写道浏览器中}});writer.write("主线程结束<br>");}}

以上代码浏览器看到的内容是:
主线程开始
主线程结束
================ 0
================ 1
================ 2
================ 3
================ 4
================ 5
================ 6
================ 7
================ 8
================ 9

说明执行顺序是主线程线执行完然后等待asyncContext.complete();执行一起把数据写到浏览器

如过将超时事件设置为 2秒打印结果如下：

主线程开始

主线程结束

================ 0

================ 1

================ 2

================ 3

================ 4

说明当超时的时候也会自动将response中的数据写到浏览器中

10.同步线程执行完成得通知 asyncContext.complete(); 如果不执行该语句主线程会一直等待异步线程的执行完成知道超时默认的超时时间是 30秒。也可以asyncContext.setTimeout(3000);修改超时时间超时之后监听器的onTimeout方法会被回调。