NoClassDefFound运行代码时logcat上的异常

Question

我正在尝试使用简单的代码通过android将文件上传到FTP服务器（实际上我尝试过其中一些代码）示例是：

package com.example.testtrials;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import org.jibble.simpleftp.SimpleFTP;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.TextView;

public class TestActivity extends Activity {

    TextView text;

    public class FTPFileUpload extends AsyncTask<String, Void, String> {

        @Override
        protected String doInBackground(String... params) {
            try {
                SimpleFTP ftp = new SimpleFTP();
                // Connect to an FTP server on port 21.
                ftp.connect(params[0], 21, params[1], params[2]);
                // Set binary mode.
                ftp.bin();
                // Change to a new working directory on the FTP server.
                ftp.cwd(params[3]);
                // You can also upload from an InputStream, e.g.
                ftp.stor(new FileInputStream(new File(params[4])), params[5]);
                // Quit from the FTP server.
                ftp.disconnect();
                text.setText("Upload Successful");
            }
            catch (IOException e) {
                // Jibble.
            }
            return null;
    }
}
        @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.testlayout);
        text = (TextView) findViewById(R.id.text);

        FTPFileUpload task = new FTPFileUpload();
        task.execute("StringArguments");
    }
}

但是logcat给了我以下错误：

07-10 14:34:49.500: E/dalvikvm(7700): Could not find class 'org.jibble.simpleftp.SimpleFTP', referenced from method com.example.testtrials.TestActivity$FTPFileUpload.doInBackground
07-10 14:34:49.500: W/dalvikvm(7700): VFY: unable to resolve new-instance 1262 (Lorg/jibble/simpleftp/SimpleFTP;) in Lcom/example/testtrials/TestActivity$FTPFileUpload;
07-10 14:34:49.500: D/dalvikvm(7700): VFY: replacing opcode 0x22 at 0x0000
07-10 14:34:49.500: D/dalvikvm(7700): DexOpt: unable to opt direct call 0x2564 at 0x02 in Lcom/example/testtrials/TestActivity$FTPFileUpload;.doInBackground
07-10 14:34:49.510: W/dalvikvm(7700): threadid=11: thread exiting with uncaught exception (group=0x41fa12b8)
07-10 14:34:49.510: E/AndroidRuntime(7700): FATAL EXCEPTION: AsyncTask #1
07-10 14:34:49.510: E/AndroidRuntime(7700): java.lang.RuntimeException: An error occured while executing doInBackground()
07-10 14:34:49.510: E/AndroidRuntime(7700):     at android.os.AsyncTask$3.done(AsyncTask.java:299)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at java.lang.Thread.run(Thread.java:856)
07-10 14:34:49.510: E/AndroidRuntime(7700): Caused by: java.lang.NoClassDefFoundError: org.jibble.simpleftp.SimpleFTP
07-10 14:34:49.510: E/AndroidRuntime(7700):     at com.example.testtrials.TestActivity$FTPFileUpload.doInBackground(TestActivity.java:23)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at com.example.testtrials.TestActivity$FTPFileUpload.doInBackground(TestActivity.java:1)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
07-10 14:34:49.510: E/AndroidRuntime(7700):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
07-10 14:34:49.510: E/AndroidRuntime(7700):     ... 5 more

我尝试过以下方法： project -> build path -> Add External Jars...也project -> properties -> Java Build Path -> Order & Export -> (All are checked)以及project -> Android Tools -> Fix Project Properties 我也试过了commons.net 3.3，但我得到了同样的错误。我重启了我的系统，没用。重新载入jar files，但徒劳无功。即使重新安装IDE及其所有包装，但似乎没有任何作用。请帮忙吗？