所以我的下一个问题是这个代码。它似乎没有找到一个方法，我的眼睛没有受过训练。有什么帮助吗？

package packeging;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Calendar;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.amazonaws.HttpMethod;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3Client;
import com.amazonaws.auth.BasicAWSCredentials;
import org.apache.http.*;
/**
 * Servlet implementation class Hashtastic
 */
@WebServlet("/Hashtastic")
public class Hashtastic extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private final static String BUCKET_NAME = "idlatestingbucket";//http://s3.amazonaws.com/THESISDB/techy.jpg
    private final static String FILE_NAME = "TestPicture/wallpaper-264411.png";
    private final static String ACCESS_KEY = "Fakepass";
    private final static String SECRET_KEY = "Fakekey";
    /**
     * Default constructor. 
     */
    public Hashtastic() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
         PrintWriter out = response.getWriter();
          Calendar cal = Calendar.getInstance();
         cal.add(Calendar.SECOND, 1000);
         Date expDate = cal.getTime();
         out.println(expDate+"\n");
        
         BasicAWSCredentials cre = new BasicAWSCredentials(ACCESS_KEY, SECRET_KEY);
        AmazonS3 s3 = new AmazonS3Client(cre);
        String url = s3.generatePresignedUrl(BUCKET_NAME, FILE_NAME, expDate, HttpMethod.GET).toString();
        out.println(url);
         out.close();
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

我得到这个500错误。它说它缺少一个方法。我的lib中有jar和Eclipse的插件。

description The server encountered an internal error () that prevented it from fulfilling this request.

exception 

javax.servlet.ServletException: Servlet execution threw an exception

root cause 

java.lang.NoSuchMethodError: org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager: method <init>()V not found
    com.amazonaws.http.ConnectionManagerFactory.createThreadSafeClientConnManager(ConnectionManagerFactory.java:26)
    com.amazonaws.http.HttpClientFactory.createHttpClient(HttpClientFactory.java:83)
    com.amazonaws.http.AmazonHttpClient.<init>(AmazonHttpClient.java:116)
    com.amazonaws.AmazonWebServiceClient.<init>(AmazonWebServiceClient.java:60)
    com.amazonaws.services.s3.AmazonS3Client.<init>(AmazonS3Client.java:291)
    com.amazonaws.services.s3.AmazonS3Client.<init>(AmazonS3Client.java:273)
    packeging.Hashtastic.doGet(Hashtastic.java:48)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.27 logs.