github地址
https://github.com/square/okhttp
//引入okhttp包
private final OkHttpClient client = new OkHttpClient();

findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) 
        try {
            run();
        } catch (Exception e) {
            e.printStackTrace();
        }
      
    }
});

//异步执行
//Asynchronous Get（异步Get）

//在一个工作线程中下载文件，当响应可读时回调Callback接口。读取响应时会阻塞当前线程。OkHttp现阶段不提供异步api来接收响应体。
public void run() throws Exception {
    Request request = new Request.Builder()
            //.url("http://publicobject.com/helloworld.txt")
            .url("http://gold.xitu.io/")
            .build();

    client.newCall(request).enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            e.printStackTrace();
        }

        @Override
        public void onResponse(Call call, Response response) throws IOException {
            if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

            Headers responseHeaders = response.headers();
            for (int i = 0, size = responseHeaders.size(); i < size; i++) {
                System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
            }

            System.out.println(response.body().string());
        }
    });
}

////////////////////////////
//开线程同步get请求

private void getRequest() {
    final Request request = new Request.Builder()
            .get()
            .tag(this)
            .url("http://gold.xitu.io")
            .build();
    new Thread(new Runnable() {
        @Override
        public void run() {
            Response response = null;
            try {
                response = client.newCall(request).execute();
                if (response.isSuccessful()) {
                    System.out.println("zzz" + response.body().string());
                    Log.i("WY", "打印GET响应的数据：" + response.body().string());
                } else {
                    throw new IOException("Unexpected code " + response);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }).start();
}

////////////////////////////////////////
///////////////////////////////
//异步get解析json 使用gson
private final OkHttpClient client = new OkHttpClient();
private final Gson gson = new Gson();

public void run5() throws Exception {
    Request request = new Request.Builder()
            .url("https://api.github.com/gists/c2a7c39532239ff261be")
            .build();
    client.newCall(request).enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            e.printStackTrace();
        }

        @Override
        public void onResponse(Call call, Response response) throws IOException {
            if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

//                Headers responseHeaders = response.headers();
//                for (int i = 0, size = responseHeaders.size(); i < size; i++) {
//                    System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
//                }
//
            // System.out.println("aaa"+response.body().string());
            Gist gist = gson.fromJson(response.body().charStream(), Gist.class);
            for (Map.Entry<String, GistFile> entry : gist.files.entrySet()) {
                System.out.println("key" + entry.getKey());
                System.out.println("content" + entry.getValue().content);
                System.out.println("type" + entry.getValue().type);
            }
        }
    });

//        Response response = client.newCall(request).execute();
//        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
//
//        Gist gist = gson.fromJson(response.body().charStream(), Gist.class);
//        for (Map.Entry<String, GistFile> entry : gist.files.entrySet()) {
//            System.out.println(entry.getKey());
//            System.out.println(entry.getValue().content);
//        }
}

static class Gist {
    Map<String, GistFile> files;
}

static class GistFile {
    String content;
    String type;
}