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.