servlet错误：HTTP Status 405

// 导入必需的 java 库
import java.io.;
import java.util.;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class UploadServlet extends HttpServlet {

private boolean isMultipart;
private String filePath;
private int maxFileSize = 50 * 1024;
private int maxMemSize = 4 * 1024;
private File file ;

public void init( ){
// 获取文件将被存储的位置
filePath =
getServletContext().getInitParameter("file-upload");
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, java.io.IOException {
// 检查我们有一个文件上传请求
isMultipart = ServletFileUpload.isMultipartContent(request);
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter( );
if( !isMultipart ){
out.println("");
out.println("");
out.println("Servlet upload");
out.println("");
out.println("");
out.println("

No file uploaded

");
out.println("");
out.println("");
return;
}
DiskFileItemFactory factory = new DiskFileItemFactory();
// 文件大小的最大值将被存储在内存中
factory.setSizeThreshold(maxMemSize);
// Location to save data that is larger than maxMemSize.
factory.setRepository(new File("c: emp"));

  // 创建一个新的文件上传处理程序
  ServletFileUpload upload = new ServletFileUpload(factory);
  // 允许上传的文件大小的最大值
  upload.setSizeMax( maxFileSize );

  try{ 
  // 解析请求，获取文件项
  List fileItems = upload.parseRequest(request);

  // 处理上传的文件项
  Iterator i = fileItems.iterator();

  out.println("<html>");
  out.println("<head>");
  out.println("<title>Servlet upload</title>");  
  out.println("</head>");
  out.println("<body>");
  while ( i.hasNext () ) 
  {
     FileItem fi = (FileItem)i.next();
     if ( !fi.isFormField () )	
     {
        // 获取上传文件的参数
        String fieldName = fi.getFieldName();
        String fileName = fi.getName();
        String contentType = fi.getContentType();
        boolean isInMemory = fi.isInMemory();
        long sizeInBytes = fi.getSize();
        // 写入文件
        if( fileName.lastIndexOf("\") >= 0 ){
           file = new File( filePath + 
           fileName.substring( fileName.lastIndexOf("\"))) ;
        }else{
           file = new File( filePath + 
           fileName.substring(fileName.lastIndexOf("\")+1)) ;
        }
        fi.write( file ) ;
        out.println("Uploaded Filename: " + fileName + "<br>");
     }
  }
  out.println("</body>");
  out.println("</html>");

}catch(Exception ex) {
System.out.println(ex);
}
}
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, java.io.IOException {

    throw new ServletException("GET method used with " +
            getClass( ).getName( )+": POST method required.");

}
}

编译运行后，会出现

如果注释掉最后的doGet方法，会报错

错误原因：
(一)出错原因是doPost方法用于处理前台提交的数据，当form表单属性method="post"时，doPost方法才被调用。当用servlet类的URL直接访问servlet时，发送的是HTTP请求，servlet默认调用doGet()方法，而源程序里没有重写父类的doGet()方法，父类的doGet()方法不被此种URL支持，所以出现HTTP method GET is not supported by this URL这种错误。
(二)HTTP请求传参：路径+请求语句，例：http://localhost:8080/test/r?age=123&name=defbv