Servlet3.0——文件上传

Servlet3.0文件上传

1.Sevlet3.0提供了一个新API来处理上传数据:

Annotation MultipartConfig: A servlet can be annotated with this annotation in order to handlemultipart/form-data requests which contain file upload data.
通过这个注解标记一个Servlet 可以处理multipart/form-data请求包含的文件上传操作。
annotation has the following options:
- - fileSizeThreshold: file’s size that is greater than this threshold will be directly written to disk, instead of saving in memory.
    如果上传的文件内容长度大于此值，将会写入磁盘而不保存在内存中。
  - location: directory where file will be stored via Part.write() method.
    文件保存的本地路径
  - maxFileSize: maximum size for a single upload file.
    单次上传文件长度最大值，此值为字节
  - maxRequestSize:maximum size for a request.
    单次上传文件长度最大值，此值为字节
    所有size单位为字节,-1L表示不限制。1024*1024*10 = 10 MB
Interface Part: represents a part in a multipart/form-data request. This interface defines some methods for working with upload data (to name a few):
- - getInputStream(): returns an InputStream object which can be used to read content of the part.
    获取上传文件的文件流
  - getSize(): returns the size of upload data, in bytes.
    文件大小
  - write(String filename): this is the convenience method to save upload data to file on disk. The file is created relative to the location specified in the MultipartConfig annotation.
New methods introduced in HttpServletRequest interface:
- getParts(): returns a collection of Part objects
  获取多个上传文件对象
- getPart(String name): retrieves an individual Part object with a given name.
  获取指定名name的上传文件对象。<input type="file" name="abc">

示例代码---服务端:

@WebServlet(urlPatterns = "/upload.html")
@MultipartConfig(fileSizeThreshold = 1024 * 1024 * 2, maxFileSize = 1024 * 1024 * 10, maxRequestSize = 1024 * 1024 * 50)
public class UploadFileServlet extends HttpServlet {
    private static final long    serialVersionUID    = 1L;
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("UploadFileServlet doPost invoked!");
        for (Part part : req.getParts()) {
            String fileName = extractFileName(part);
            part.write("D://xxx_"+fileName);
            
            /*
             * System.out.println("fileName=" + fileName); InputStream is =
             * null; OutputStream os = null; try { is = part.getInputStream();
             * os = new FileOutputStream(new File("D://xxx_" + fileName));
             * byte[] buf = new byte[1024]; int len = 0; while ((len =
             * is.read(buf)) != -1) { os.write(buf, 0, len); } } catch
             * (Exception e) { } finally { if (is != null) { os.close();
             * is.close(); } }
             */
        }
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().println("上传文件成功!");
        resp.getWriter().close();
    }
    /**
     * Extracts file name from HTTP header content-disposition
     */
    private String extractFileName(Part part) {
        String contentDisp = part.getHeader("content-disposition");
        String[] items = contentDisp.split(";");
        for (String s : items) {
            if (s.trim().startsWith("filename")) {
                return s.substring(s.indexOf("=") + 2, s.length() - 1);
            }
        }
        return "";
    }
}

客户端：此处使用Jsoup代码的方式上传文件，而不是通过浏览器。不熟悉Jsoup的可以参数我另一篇博文“ HttpClient/Jsoup 请求”

public static void main(String[] args) {
		InputStream is = null;
		try {
			String url = "http://localhost:8080/part1/upload.html";
			is = new FileInputStream(new File("D://abc.txt"));
			Response response = Jsoup.connect(url).data("gdr", "abcc.txt", is).method(Method.POST).execute();
			System.out.println(response.body());
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			if (is != null) {
				try {
					is.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}

输出：

上传文件成功!

注：该代码在Eclipse-Jetty插件中运行，一直没有将文件写入D://下。但在Tomcat中运行，一切正常。

造成这种现象很容易理解，Servlet为接口规范，其实现为各Web容器。

因此建议在保存文件时为了保证在各种Web容器中运行都有一至结果，建议通过Part接口获取文件输入流，自己实现文件保存功能。如示例中的注释。

Servlet3.0——文件上传

1.Sevlet3.0提供了一个新API来处理上传数据:

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