public class LoginServlet extends HttpServlet {

    /**

     * The doGet method of the servlet. <br>

     *

     * This method is called when a form has its tag value method equals to get.

     *

     * @param request the request send by the client to the server

     * @param response the response send by the server to the client

     * @throws ServletException if an error occurred

     * @throws IOException if an error occurred

     */

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        //getParameter 方法中默认使用iso-8859-1对接收到的参数进行转码

        String username = request.getParameter("username");

        String password = request.getParameter("password");

        // 把乱码的字符串的字节打回原形,转成UTF-8

        String newUsername = new String(username.getBytes("iso-8859-1"),"UTF-8");

        String newPassword = new String(password.getBytes("iso-8859-1"),"UTF-8");

        System.out.println("newUsername:"+newUsername+",newPassword:"+newPassword);

        // tomcat默认使用iso-8859-1转码,但是iso-8859-1不支持中文,tomcat会查看操作系统的本地码表,本地字符集编码是gbk

        if("123".equals(newUsername) && "abc".equals(newPassword)){

            response.getOutputStream().write("login success".getBytes());

        }else{

            response.getOutputStream().write("login failture".getBytes());

        }

    }

    /**

     * The doPost method of the servlet. <br>

     *

     * This method is called when a form has its tag value method equals to post.

     *

     * @param request the request send by the client to the server

     * @param response the response send by the server to the client

     * @throws ServletException if an error occurred

     * @throws IOException if an error occurred

     */

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}

public class MainActivity extends Activity {

	private EditText et_qq;

	private EditText et_pwd;

	private String path = "http://192.168.7.171:8080/web/servlet/LoginServlet";

	private Handler handler = new Handler(){

		public void handleMessage(android.os.Message msg) {

			String result = (String) msg.obj;

			Toast.makeText(MainActivity.this, result, 0).show();

		};

	};

	@Override

	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);

		setContentView(R.layout.activity_main);

		// 得到两个输入框

		et_qq = (EditText) findViewById(R.id.et_qq);

		et_pwd = (EditText) findViewById(R.id.et_pwd);

	}

	public void login(View v){

		// 以get方式向服务器端提交数据

		final String qq = et_qq.getText().toString().trim();

		final String pwd = et_pwd.getText().toString().trim();

		if(TextUtils.isEmpty(qq) || TextUtils.isEmpty(pwd)){

			Toast.makeText(this, "qq号码和密码都不能为空", 0).show();

			return;

		}else{

			new Thread(){

				public void run() {

					try {

						// 1.创建一个URL对象,打开一个http类型的连接

						URL url = new URL(path);

						HttpURLConnection conn = (HttpURLConnection) url.openConnection();

						String data = "username="+qq+"&password="+pwd;

						// 2.给连接设置请求参数

						conn.setRequestMethod("POST");

						conn.setConnectTimeout(3000); // 设置连接的超时时间

						conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

						conn.setRequestProperty("Content-Length", data.length()+"");

						//conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko");

						// 以二进制流的形式写到服务器端;

						// 设置是否允许把数据写到服务器端,true表示允许,false表示不允许

						conn.setDoOutput(true);

						conn.getOutputStream().write(data.getBytes());

						// 3.得到服务器端返回的响应码是否为200,应该接收服务器端返回的二进制输入流

						// 得到服务器端返回的响应码

						int code = conn.getResponseCode();

						if(code == 200){

							//接收服务器端返回的二进制输入流

							InputStream is = conn.getInputStream();

							String result = StreamTools.readStream(is);

							Message msg = Message.obtain();

							msg.obj = result;

							handler.sendMessage(msg);

						}

					} catch (Exception e) {

						e.printStackTrace();

					}

				};

			}.start();

		}

	}

}

public class StreamTools {

    /**

     * 把二进制数据转换成字符串

     * @param is

     * @return

     */

    public static String readStream(InputStream is) {

        String result = null;

        //  创建一个输出流,用于写数据

        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        try {

            int len = -1;

            byte[] buffer = new byte[1024];

            while((len = is.read(buffer)) != -1){

                baos.write(buffer, 0, len);

            }

            result = baos.toString();

        } catch (Exception e) {

            e.printStackTrace();

        }

        return result;

    }

}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

   android:orientation="vertical">

    <EditText

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:hint="请输入qq号码"

        android:id="@+id/et_qq" />

    <EditText

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:hint="请输入密码"

        android:id="@+id/et_pwd" />

    <Button

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="登陆"

        android:onClick="login"

        />

</LinearLayout>