涉及到的 知識點：

1.安卓UI元件menu

2.OkHttp框架

3.Executors（執行緒池）

OkHttp結構簡介

案例程式碼

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import java.io.IOException;
import
 
 java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.Headers;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

public class MainActivity
 
 extends AppCompatActivity {

    private static final String TAG = "MainActivity-xx";

    //服務端指定型別
    private static final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("text/x-markdown; charset=utf-8");

    private static final String POST_URL = "https://api.github.com/markdown/raw";

    public static
 
 final String GET_URL = "http://www.imooc.com/api/teacher?type=2";

    public final OkHttpClient mClient = new OkHttpClient();

    private TextView mContentTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mContentTextView = (TextView) findViewById(R.id.tvContent);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        //獲取menu泵，載入menu資源
        getMenuInflater().inflate(R.menu.actions, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.menuGet:
                getToSync();
                break;
            case R.id.menuResponse:
                getToAsync();
                break;
            case R.id.menuPost:
                post();
                break;
        }
        return super.onOptionsItemSelected(item);
    }

    private void post() {
        Request.Builder builder = new Request.Builder();
        builder.url(POST_URL);
        //***************************服務端設定的資料型別****************提交的資料***************************
        builder.post(RequestBody.create(MEDIA_TYPE_MARKDOWN, "Hello world github/linguist#1 **cool**, and #1!"));
        Request request = builder.build();
        Call call = mClient.newCall(request);
        call.enqueue(new Callback() {

            @Override
            public void onFailure(Call call, IOException e) {
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                if (response.isSuccessful()) {
                    final String content = response.body().string();
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            mContentTextView.setText(content);
                        }
                    });
                }
            }
        });
    }

    private void getToSync() {
        ExecutorService executor = Executors.newSingleThreadExecutor();
        executor.submit(new Runnable() {
            @Override
            public void run() {
                Request.Builder builder = new Request.Builder();
                builder.url(GET_URL);
                Request request = builder.build();
                Log.d(TAG, "run: " + request);
                Call call = mClient.newCall(request);
                try {
                    //同步請求
                    Response response = call.execute();
                    if (response.isSuccessful()) {
                        final String string = response.body().string();
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                mContentTextView.setText(string);
                            }
                        });
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
        executor.shutdown();
    }

    private void getToAsync() {
        Request.Builder bulider = new Request.Builder();
        bulider.url(GET_URL);
        Request request = bulider.build();
        Call call = mClient.newCall(request);
        //非同步請求
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                int code = response.code();
                Headers headers = response.headers();
                String content = response.body().string();
                final StringBuilder sb = new StringBuilder();
                sb.append("code: " + code).append("\nheaders: " + headers).append("\ncontent: " + content);
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        mContentTextView.setText(sb.toString());
                        Log.d(TAG, "run() called with: " + "" + sb);
                    }
                });
            }
        });
    }
}