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:

 1 /**
 2  * Created by IntelliJ IDEA.
 3  *
 4  * @Auther: ShaoHsiung
 5  * @Date: 2018/9/5 16:36
 6  * @Title: 01 演示@WebServlet的使用
 7  * @Description: name, urlpatterns, initparams(配合@WebInitParam使用), loadOnStartup
 8  */
 9 @WebServlet(name = "MyWebServlet", urlPatterns = {"/servlet/MyWebServlet", "/servlet/WebServlet"},
10         initParams = { @WebInitParam(name = "Site :", value = "http://roseindia.net"),
11         @WebInitParam(name = "Rose", value = "India", description = "detail-info")}, loadOnStartup = 1)
12 public class MyWebServlet extends HttpServlet {
13     @Override
14     public void init(ServletConfig config) throws ServletException {
15         Enumeration<String> initParameterNames = config.getInitParameterNames();
16         while (initParameterNames.hasMoreElements()) {
17             String name = initParameterNames.nextElement();
18             String value = config.getInitParameter(name);
19             System.out.println("该Servlet的初始化参数为: " + name + "=" + value);
20         }
21     }
22 
23     @Override
24     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
25 
26         // 通知浏览器读取格式
27         resp.setContentType("text/html;charset=utf-8");
28 
29         Writer out = resp.getWriter();
30 
31         out.write("测试Servlet3.0!!!");
32     }
33 
34     @Override
35     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
36         doGet(req, resp);
37     }
38 }

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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:

 1 /**
 2  * Created by IntelliJ IDEA.
 3  *
 4  * @Auther: ShaoHsiung
 5  * @Date: 2018/9/5 20:24
 6  * @Title:
 7  * @Description:
 8  */
 9 @WebListener
10 public class MyWebListener implements ServletContextListener {
11     @Override
12     public void contextInitialized(ServletContextEvent servletContextEvent) {
13         System.out.println("监听器初始化");
14     }
15 
16     @Override
17     public void contextDestroyed(ServletContextEvent servletContextEvent) {
18         System.out.println("监听器销毁");
19     }
20 }

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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:

 1 /**
 2  * Created by IntelliJ IDEA.
 3  *
 4  * @Auther: ShaoHsiung
 5  * @Date: 2018/9/5 17:01
 6  * @Title: 02 演示@WebFilter的使用
 7  * @Description: filterName属性: 过滤器的名称; value或urlpatterns属性: 过滤器拦截的url映射
 8  */
 9 @WebFilter(filterName = "MyWebFilter", value = "/servlet/MyWebServlet")
10 public class MyWebFilter implements Filter {
11     @Override
12     public void init(FilterConfig filterConfig) throws ServletException {
13         System.out.println("过滤器初始化");
14     }
15 
16     @Override
17     public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
18         System.out.println("过滤器执行");
19         // 放行
20         filterChain.doFilter(servletRequest, servletResponse);
21     }
22 
23     @Override
24     public void destroy() {
25         System.out.println("过滤器销毁");
26     }
27 }

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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:

 1 /**
 2  * Created by IntelliJ IDEA.
 3  *
 4  * @Auther: ShaoHsiung
 5  * @Date: 2018/9/5 17:07
 6  * @Title: 03 演示servlet3.0原生文件上传
 7  * @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,
 8  *               开发者通过part对象来对上传的文件进行操作.
 9  */
10 @WebServlet(urlPatterns = {"/servlet/fileupload"})
11 @MultipartConfig  // 标识servlet支持原生文件上传
12 public class FileUploadServlet extends HttpServlet {
13     @Override
14     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
15 
16         // 字符编码设置
17         req.setCharacterEncoding("utf-8");
18         resp.setCharacterEncoding("utf-8");
19         resp.setContentType("text/html;charset=utf-8");
20 
21         // 获取out对象
22         PrintWriter out = resp.getWriter();
23 
24         // 获取上传文件存储路径
25         String realPath = req.getServletContext().getRealPath("/WEB-INF/upload");
26         File file = new File(realPath);
27         if (!file.exists()) {
28             file.mkdirs();
29             System.out.println("目录创建成功!");
30         }
31         // 通过request对象获取part
32         Collection<Part> parts = req.getParts();
33         if (parts.size() == 1) {  // 单文件上传
34             // 通过input标签的name属性获取上传文件
35             Part part = req.getPart("file1");
36             // 从请求头中解析文件名称
37             String header = part.getHeader("content-disposition");
38             String fileName = getFileName(header);
39             // 保存文件
40             part.write(realPath + File.separator + fileName);
41         } else {  // 多文件上传
42             // 迭代parts
43             for (Part part : parts) {
44                 // 获取到part对象之后, 操作步骤与单文件上传相同
45                 String header = part.getHeader("content-disposition");
46                 String fileName = getFileName(header);
47                 part.write(realPath + File.separator + fileName);
48             }
49         }
50 
51         out.println("上传成功!");
52         out.close();
53     }
54 
55     /**
56      * 从请求头中解析上传文件名
57      * @param header part的请求头
58      * @return 上传文件名
59      */
60     public String getFileName(String header) {
61         String[] tempArr1 = header.split(";");
62         String[] tempArr2 = tempArr1[2].split("=");
63 
64         String fileName = tempArr2[1].substring(tempArr2[1].lastIndexOf("\\")+1).replaceAll("\"", "");
65         return fileName;
66     }
67 }

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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.