引言
当在HTML或者JavaScript中使用表单提交数据时，默认编码格式为application/x-www-form-urlencoded，在HTTP报文中可以找到用&与=隔开的信息（因此，我们也可以在JavaScript中手动的send它们），类似下面：
这种格式可以直接被getParameter获取，但也只能用于传输文本，对于二进制数据是无能为力的。
文件传输需要用到multipart/form-data（注意在JavaScript不要直接设置它，因为二进制数据必须有边界作为数据的结尾，不设置它，JS会自动帮我们加上），类似下面这样：
网上给的方案要么很麻烦（其实是我这个非专业Java选手看不懂），要么牛头不对马嘴，经过搜索我找到两种方案来解决。
@MultipartConfig
该答案源自stackoverflow，非常简单高效。
If you are working in servlet 3.0+ environment, you can also use its multipart support to easily finish the multipart-data parsing job. Simply add an @MultipartConfig on the servlet class, then you can receive the text data by calling request.getParameter(), very easy.
直接在对应的Servlet上加上@MultipartConfig即可，该注释会自动解析来自multipart/form-data的数据，使得getParameter能够获取到，此外对于文件我们直接只用用getPart获取，比下面的FileUpload要来的方便的多。
FileUpload
这是Apache给的工具包，具体用法就不赘述了，可以参考下面：
package LearnWeb;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import java.io.File;
import java.io.IOException;
import java.util.List;
import java.util.UUID;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/serv25")
public class Servlet25 extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
FileItemFactory factory = new DiskFileItemFactory();
ServletFileUpload sf = new ServletFileUpload(factory);
try {
if (!ServletFileUpload.isMultipartContent(req)) {
throw new Exception("no multipartcontent");
}
List<FileItem> formData = sf.parseRequest(req);
for (FileItem fi : formData) {
if (fi.isFormField()) {
System.out.println("field_name:" + fi.getFieldName() + ":" + fi.getString("UTF-8"));
switch (fi.getFieldName()) {
case "name":
System.out.println("receive name");
break;
default:
System.out.println("unknow data");
}
} else {
String image_name = fi.getName();
System.out.println("image_name:" + image_name);
if (image_name != "") {
String image_dir_path = req.getServletContext().getRealPath("/images/");
File image_dir = new File(image_dir_path);
if (!image_dir.exists()) {
image_dir.mkdir();
}
String file_name = UUID.randomUUID().toString();
String suffix = image_name.substring(fi.getName().lastIndexOf("."));
System.out.println("image_dir_path:" + image_dir_path);
System.out.println("file_name:" + file_name);
System.out.println("suffix:" + suffix);
fi.write(new File(image_dir_path, file_name + suffix));
} else {
throw new Exception("no file receive");
}
}
}
resp.getWriter().write("true");
} catch (Exception e) {
e.printStackTrace();
resp.getWriter().write("false");
}
}
}
另外附上下载链接：
FileUpload – Download Apache Commons FileUpload
Commons IO – Download Apache Commons IO
参考
java - How can my Servlet receive parameters from a multipart/form-data form? - Stack Overflow