GET

HttpClient client = new DefaultHttpClient();

// パラメータの設定
ArrayList<NameValuePair> value = new ArrayList<NameValuePair>();
value.add( new BasicNameValuePair("key1", "value1"));
value.add( new BasicNameValuePair("key2", "value2"));
value.add( new BasicNameValuePair("key3", "value3"));

String responseData = null;

 try {
    String query = URLEncodedUtils.format(value, "UTF-8");
    HttpGet get = new HttpGet("URL" + "?" + query);

    // リクエスト送信
    HttpResponse response = client.execute(get);
    // 取得
    HttpEntity entity = response.getEntity();
    responseData = EntityUtils.toString(entity, "UTF-8");
} catch(IOException e) {
    e.printStackTrace();
}

POST

HttpClient client = new DefaultHttpClient();
HttpPost post = new HttpPost("URL");

// パラメータの設定
ArrayList<NameValuePair> value = new ArrayList<NameValuePair>();
value.add( new BasicNameValuePair("key1", "value1"));
value.add( new BasicNameValuePair("key2", "value2"));
value.add( new BasicNameValuePair("key3", "value3"));

String responseData = null;

try {
    post.setEntity(new UrlEncodedFormEntity(value, "UTF-8"));// 文字コード変換
    // リクエスト送信
    HttpResponse response = client.execute(post);
    // 取得
    HttpEntity entity = response.getEntity();
    responseData = EntityUtils.toString(entity, "UTF-8");
} catch(IOException e) {
    e.printStackTrace();
}