Servlet实现文件上传

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