从Java Servlet使用AWS SimpleDB创建域

Question

I am a university student working on a research project that involves migrating a web application to Amazon's cloud. I spent the last semester working with servlets and was able to get the majority of the app's functionality working using a java servlet running in Tomcat.

I am now trying to integrate Amazon Web Services such as the SimpleDB and E-mail service. I develop using the Eclipse Java EE for Web Developers Indigo IDE. I have the AWS plugin installed and am able to run sample code that Amazon provides to call SDB and SES successfully.

However when I attempt to call a service like simpleDB from the servlet either directly or through a separate class I receive the following error:

HTTP Status 500 -

type Exception report

message

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

exception

javax.servlet.ServletException: Error instantiating servlet class org.comtor.cloud.api.APIservlet org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:928) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987) org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:539) org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:298) java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) java.lang.Thread.run(Thread.java:680) root cause

java.lang.NoClassDefFoundError: com/amazonaws/auth/AWSCredentials java.lang.Class.getDeclaredConstructors0(Native Method) java.lang.Class.privateGetDeclaredConstructors(Class.java:2389) java.lang.Class.getConstructor0(Class.java:2699) java.lang.Class.newInstance0(Class.java:326) java.lang.Class.newInstance(Class.java:308) org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:928) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987) org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:539) org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:298) java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) java.util. concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) java.lang.Thread.run(Thread.java:680) root cause

java.lang.ClassNotFoundException: com.amazonaws.auth.AWSCredentials org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1688) org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1533) java.lang.Class.getDeclaredConstructors0(Native Method) java.lang.Class.privateGetDeclaredConstructors(Class.java:2389) java.lang.Class.getConstructor0(Class.java:2699) java.lang.Class.newInstance0(Class.java:326) java.lang.Class.newInstance(Class.java:308) org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:928) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987) org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:539) org.a pache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:298) java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) java.lang.Thread.run(Thread.java:680) note The full stack trace of the root cause is available in the Apache Tomcat/7.0.23 logs.

Apache Tomcat/7.0.23

My code looks like this:

package org.comtor.cloud.api;

import java.io.*;
import javax.servlet.http.*;
import javax.servlet.*;

import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.simpledb.AmazonSimpleDBClient;
import com.amazonaws.services.simpledb.model.CreateDomainRequest;

import java.io.IOException;

@SuppressWarnings("serial")
public class APIservlet extends HttpServlet {
  public void doGet (HttpServletRequest request,
                     HttpServletResponse response)
    throws ServletException, IOException
  {
      doPost(request, response);
  }
  public void doPost(HttpServletRequest request,
          HttpServletResponse response)
                  throws ServletException, IOException {
        PrintWriter out = response.getWriter();

        // AWS Credentials
        String sAccessKey = "myAccessKey";
        String sSecretKey = "mySecretKey";

        // Authenticate AWS account
        BasicAWSCredentials oAWSCredentials = new BasicAWSCredentials(sAccessKey, sSecretKey);
        AmazonSimpleDBClient awsSimpleDBClient = new AmazonSimpleDBClient(oAWSCredentials);

        // Try to access simpleDB
        try 
        {
            System.out.println("Connecting to Simple Database");
            // Create a domain
            String myDomain = "MyStore";
            System.out.println("Creating domain called " + myDomain + ".\n");
            awsSimpleDBClient.createDomain(new CreateDomainRequest(myDomain));
            System.out.println("Connection Made");

        } 
        // Print Error Stack Trace
        catch (NoSuchAlgorithmException e) 
        {
            e.printStackTrace();
        }

        // Close PrintWriter
        out.close();
  }
}

** Access & Secret Keys removed from code **

The same goes for SES. I have also tried using a java library like 'typica' and still receive a NoClassDef error. I have the AWS library in my build path under the libraries folder and the jar package / classes seem to be there. So I am unsure why I am unable to use these classes to interact with simpleDB from my servlet.

I'd greatly appreciate any help on this matter. I believe I am not fully understanding how to call AWS SDB from a web environment.

Thank you.

Answer 1

java.lang.ClassNotFoundException: com.amazonaws.auth.AWSCredentials indicates that this class is not on your classpath. Make sure that the jar containing the com.amazonaws.auth.AWSCredentials class is included in your web application's WEB-INF/lib folder.