Servlet3.0要点小结

1. 注解配置Servlet

@WebServlet

name属性: servlet名称

value属性或urlPatterns属性: servlet映射路径, 可配置多个

initParams属性: 初始化参数, 配合@WebInitParam一起使用

loadOnStartup属性: 为1表示web容器启动时就初始化servlet

测试代码:

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/9/5 16:36
  * @Title: 01 演示@WebServlet的使用
  * @Description: name, urlpatterns, initparams(配合@WebInitParam使用), loadOnStartup
  */
 @WebServlet(name = "MyWebServlet", urlPatterns = {"/servlet/MyWebServlet", "/servlet/WebServlet"},
         initParams = { @WebInitParam(name = "Site :", value = "http://roseindia.net"),
         @WebInitParam(name = "Rose", value = "India", description = "detail-info")}, loadOnStartup = 1)
 public class MyWebServlet extends HttpServlet {
     @Override
     public void init(ServletConfig config) throws ServletException {
         Enumeration<String> initParameterNames = config.getInitParameterNames();
         while (initParameterNames.hasMoreElements()) {
             String name = initParameterNames.nextElement();
             String value = config.getInitParameter(name);
             System.out.println("该Servlet的初始化参数为: " + name + "=" + value);
         }
     }

     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         // 通知浏览器读取格式
         resp.setContentType("text/html;charset=utf-8");

         Writer out = resp.getWriter();

         out.write("测试Servlet3.0!!!");
     }

     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doGet(req, resp);
     }
 }

2. 注解配置监听器

1. Servlet监听器本质?

实现监听器接口的Java程序, 如实现ServletContextListener接口的Java程序

2. 如何使用注解配置监听器

@WebListener

在Servlet监听器上添加@WebListener

测试代码:

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/9/5 20:24
  * @Title:
  * @Description:
  */
 @WebListener
 public class MyWebListener implements ServletContextListener {
     @Override
     public void contextInitialized(ServletContextEvent servletContextEvent) {
         System.out.println("监听器初始化");
     }

     @Override
     public void contextDestroyed(ServletContextEvent servletContextEvent) {
         System.out.println("监听器销毁");
     }
 }

3. 注解配置过滤器

@WebFilter

filterName属性: 监听器名称

value属性或urlpatterns属性: 过滤器拦截的url映射, 可配置多个

测试代码:

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/9/5 17:01
  * @Title: 02 演示@WebFilter的使用
  * @Description: filterName属性: 过滤器的名称; value或urlpatterns属性: 过滤器拦截的url映射
  */
 @WebFilter(filterName = "MyWebFilter", value = "/servlet/MyWebServlet")
 public class MyWebFilter implements Filter {
     @Override
     public void init(FilterConfig filterConfig) throws ServletException {
         System.out.println("过滤器初始化");
     }

     @Override
     public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
         System.out.println("过滤器执行");
         // 放行
         filterChain.doFilter(servletRequest, servletResponse);
     }

     @Override
     public void destroy() {
         System.out.println("过滤器销毁");
     }
 }

4. 原生文件上传

1. 原生文件上传原理: servlet3.0将multipart/form-data的post请求封装成part对象, 开发者通过part对象来对上传的文件进行操作.

2. @MultipartConfig的作用:

标识servlet支持原生文件上传

测试代码:

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/9/5 17:07
  * @Title: 03 演示servlet3.0原生文件上传
  * @Description: 原生文件上传原理: servlet3.0将multipart/form-data的post请求封装成part对象,
  *               开发者通过part对象来对上传的文件进行操作.
  */
 @WebServlet(urlPatterns = {"/servlet/fileupload"})
 @MultipartConfig  // 标识servlet支持原生文件上传
 public class FileUploadServlet extends HttpServlet {
     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         // 字符编码设置
         req.setCharacterEncoding("utf-8");
         resp.setCharacterEncoding("utf-8");
         resp.setContentType("text/html;charset=utf-8");

         // 获取out对象
         PrintWriter out = resp.getWriter();

         // 获取上传文件存储路径
         String realPath = req.getServletContext().getRealPath("/WEB-INF/upload");
         File file = new File(realPath);
         if (!file.exists()) {
             file.mkdirs();
             System.out.println("目录创建成功!");
         }
         // 通过request对象获取part
         Collection<Part> parts = req.getParts();
         if (parts.size() == 1) {  // 单文件上传
             // 通过input标签的name属性获取上传文件
             Part part = req.getPart("file1");
             // 从请求头中解析文件名称
             String header = part.getHeader("content-disposition");
             String fileName = getFileName(header);
             // 保存文件
             part.write(realPath + File.separator + fileName);
         } else {  // 多文件上传
             // 迭代parts
             for (Part part : parts) {
                 // 获取到part对象之后, 操作步骤与单文件上传相同
                 String header = part.getHeader("content-disposition");
                 String fileName = getFileName(header);
                 part.write(realPath + File.separator + fileName);
             }
         }

         out.println("上传成功!");
         out.close();
     }

     /**
      * 从请求头中解析上传文件名
      * @param header part的请求头
      * @return 上传文件名
      */
     public String getFileName(String header) {
         String[] tempArr1 = header.split(";");
         String[] tempArr2 = tempArr1[2].split("=");

         String fileName = tempArr2[1].substring(tempArr2[1].lastIndexOf("\\")+1).replaceAll("\"", "");
         return fileName;
     }
 }

要点:

1) part对象代表一个上传文件

2) 通过request对象获取part对象

3) 由于servlet3.0没有提供直接获取文件名称的方法, 所以文件名称可以通过part对象获取请求头后, 自己解析.