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  • Servlet实现文件上传

    Servlet3.0开始新增了Part接口,专门用来处理文件上传。

    package javax.servlet.http;
    
    import java.io.IOException;
    import java.io.InputStream;
    import java.util.Collection;
    public interface Part {
        public InputStream getInputStream() throws IOException;
        public String getContentType();//获得内容属性如image/png
        public String getName();//获得input name属性值与request.getPart参数值一致
        public String getSubmittedFileName();//获得上传文件名
        public long getSize();
        public void write(String fileName) throws IOException;//将上传内容写入文件
        public void delete() throws IOException;
        public String getHeader(String name);//根据标头名称返回标头信息
        public Collection<String> getHeaders(String name);//根据标头名称返回标头信息集合
        public Collection<String> getHeaderNames();//返回标头名称集合
    }

    比较重要的几个方法:

    /**
     * Obtain the content type passed by the browser.
     *
     * @return The content type passed by the browser or <code>null</code> if
     *         not defined.
     */
    public String getContentType();
    获得文件类型信息,如image/jpeg;image/png。

    /**
     * If this part represents an uploaded file, gets the file name submitted
     * in the upload. Returns {@code null} if no file name is available or if
     * this part is not a file upload.
     *
     * @return the submitted file name or {@code null}.
     *
     * @since Servlet 3.1
     */
    public String getSubmittedFileName();
    获得上传文件名称,如test.jpg

    /**
     * A convenience method to write an uploaded part to disk. The client code
     * is not concerned with whether or not the part is stored in memory, or on
     * disk in a temporary location. They just want to write the uploaded part
     * to a file.
     *
     *  This method is not guaranteed to succeed if called more than once for
     *  the same part. This allows a particular implementation to use, for
     *  example, file renaming, where possible, rather than copying all of the
     *  underlying data, thus gaining a significant performance benefit.
     *
     * @param fileName  The location into which the uploaded part should be
     *                  stored. Relative locations are relative to {@link
     *                  javax.servlet.MultipartConfigElement#getLocation()}
     *
     * @throws IOException if an I/O occurs while attempting to write the part
     */
    public void write(String fileName) throws IOException;
    上传文件。

    /**
     * Obtain the size of this part.
     *
     * @return The size of the part if bytes
     */
    public long getSize();
    获得上传文件大小(字节)。

    Demo:

    upload.html

    <!DOCTYPE html>
    <html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>upload</title>
    </head>
    <body>
        <form action="upload.do" method="post" enctype="multipart/form-data">
            上传图片:<input type="file" name="photo" value="" />
            <br />
            <input type="submit" value="上传" name="upload" />
        </form>
    </body>
    </html>
    uploadServlet.java
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.Part;
    import java.io.IOException;
    import java.io.PrintWriter;
    import java.time.LocalDate;
    import java.time.LocalTime;
    import java.time.format.DateTimeFormatter;
    //import javax.servlet.annotation.MultipartConfig;
    //import javax.servlet.annotation.WebServlet;
    
    /**
     * Created by N3verL4nd on 2017/1/9.
     */
    //@MultipartConfig(location = "D:/JAVA/IdeaProjects/JavaProj/out/artifacts/jspRun_war_exploded/upload")
    //@WebServlet(name = "uploadServlet", urlPatterns = {"/upload.do"})
    public class uploadServlet extends HttpServlet {
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            request.setCharacterEncoding("UTF-8");
            response.setContentType("text/html;charset=UTF-8");
    
            PrintWriter out = response.getWriter();
            Part part = request.getPart("photo");
    
            //获得上传文件名称(实际过程中应该重命名自己想要的格式)
            String filename = part.getSubmittedFileName();
    
            //类型检查如:只要图片格式文件
            if (part.getContentType().startsWith("image")) {
                String finalFileName = getPreFileName() + filename.substring(filename.indexOf('.', 0), filename.length());
                //写入文件
                //part.write(finalFileName);
                out.println("<h2>" + finalFileName + "  上传成功</h2>");
            }
            else {
                out.println("<h2>上传失败</h2>");
            }
            //返回input标签name值(与request.getPart参数一致)
            //out.println(part.getName());
    
            /*//返回标头名称集合(如content-disposition;content-type)
            for (String str : part.getHeaderNames()){
                out.println(str + "<br />");
            }*/
    
            /*//根据标头名称返回标头详细信息(如form-data; name="photo"; filename="ing.png")
            for (String str : part.getHeaders("content-disposition")){
                out.println(str + "<br />");
            }*/
    
            /*
            //返回内容类型
            out.println(part.getContentType() + "<br />");
            //返回标头信息
            out.println(part.getHeader("content-disposition") + "<br />");
            //返回上传文件大小
            out.println(part.getSize() + " 字节");
            //返回上传文件名
            out.println(part.getSubmittedFileName());
            */
            //out.println(this.getServletContext().getRealPath("upload"));
        }
    
        //随机生成文件名
        private String getPreFileName(){
            StringBuilder stringBuilder = new StringBuilder();
            LocalDate date = LocalDate.now();
            //格式化日期字符串
            stringBuilder.append(date.format(DateTimeFormatter.BASIC_ISO_DATE));
            LocalTime time = LocalTime.now().withNano(0);
            //格式化时间字符串
            stringBuilder.append(time.format(DateTimeFormatter.ofPattern("HHmmss")));
            return stringBuilder.toString();
        }
    
    }
    


    上传服务器文件名如:20170109214600.png

    关于MultipartConfig:

    @MultipartConfig

    该注解主要是为了辅助 Servlet 3.0 中 HttpServletRequest 提供的对上传文件的支持。该注解标注在 Servlet 上面,以表示该 Servlet 希望处理的请求的 MIME 类型是 multipart/form-data。另外,它还提供了若干属性用于简化对上传文件的处理。具体如下:

    表 5. @MultipartConfig 的常用属性

    属性名 类型 是否可选 描述
    fileSizeThreshold int 当数据量大于该值时,内容将被写入文件。
    location String 存放生成的文件地址。
    maxFileSize long 允许上传的文件最大值。默认值为 -1,表示没有限制。
    maxRequestSize long 针对该 multipart/form-data 请求的最大数量,默认值为 -1,表示没有限制。





    Keep it simple!
    作者:N3verL4nd
    知识共享,欢迎转载。
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  • 原文地址:https://www.cnblogs.com/lgh1992314/p/6616243.html
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