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.javaimport 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。 |