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Servlet实现文件上传

2017-01-09 17:15 281 查看
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
fileSizeThresholdint是当数据量大于该值时，内容将被写入文件。
locationString是存放生成的文件地址。
maxFileSizelong是允许上传的文件最大值。默认值为 -1，表示没有限制。
maxRequestSizelong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。
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