开始使用

在app目录下的build.gradle中添加依赖：

implementation 'com.squareup.okhttp3:okhttp:3.13.1'
implementation 'com.squareup.okio:okio:2.2.2'

GET方法

OkHttpClient client = new OkHttpClient.Builder().build();
Request.Builder builder = new Request.Builder().url(url);
builder.method("GET", null);
Request request = builder.build();
Call call = client.newCall(request);
call.enqueue(new Callback() {
    @Override
    public void onFailure(Call call, IOException e) {
        ...
    }

    @Override
    public void onResponse(Call call, Response response) throws IOException {
        ...
    }
});

GET参数的传递可以使用拼接字符串的方式直接拼接到url中。

POST方法

OkHttpClient client = new OkHttpClient.Builder().build();
FormBody.Builder formBody = new FormBody.Builder();
formBody.add(key,value);
... // 添加参数
RequestBody form = formBody.build();
Request.Builder builder = new Request.Builder();
Request request = builder.post(form)
        .url(url)
        .build();
Call call = client.newCall(request);
call.enqueue(new Callback() {
    @Override
    public void onFailure(Call call, IOException e) {
        ...
    }

    @Override
    public void onResponse(Call call, Response response) throws IOException {
        ...
    }
});

封装

由于OkHttp发送请求的方式比较繁琐，需要构建许多参数，所以需要我们自己进行封装，以下是我的封装方式:

/**
- @author:y4ngyy
*/

public class HttpClient {
    private OkHttpClient client;
    private static HttpClient mClient;
    private Context context;
    private HttpClient(Context c) {
        context = c;
        client = new OkHttpClient.Builder()
                .cookieJar(new PersistentCookieJar(new SetCookieCache(), new SharedPrefsCookiePersistor(context)))
                .followRedirects(true)
                .followSslRedirects(true)
                .build();
    }

    public static HttpClient getInstance(Context c){
        if (mClient == null) {
            mClient = new HttpClient(c);
        }
        return  mClient;
    }


    // GET方法
    public void get(String url, HashMap<String,String> param, MyCallback callback) {
        // 拼接请求参数
        if (!param.isEmpty()) {
            StringBuffer buffer = new StringBuffer(url);
            buffer.append('?');
            for (Map.Entry<String,String> entry: param.entrySet()) {
                buffer.append(entry.getKey());
                buffer.append('=');
                buffer.append(entry.getValue());
                buffer.append('&');
            }
            buffer.deleteCharAt(buffer.length()-1);
            url = buffer.toString();
        }
        Request.Builder builder = new Request.Builder().url(url);
        builder.method("GET", null);
        Request request = builder.build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                callback.failed(e);
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                callback.success(response);
            }
        });
    }

    public void get(String url, MyCallback callback) {
        get(url, new HashMap<String, String>(), callback);
    }

    // POST 方法
    public void post(String url, HashMap<String, String> param, MyCallback callback) {
        FormBody.Builder formBody = new FormBody.Builder();
        if(!param.isEmpty()) {
            for (Map.Entry<String,String> entry: param.entrySet()) {
                formBody.add(entry.getKey(),entry.getValue());
            }
        }
        RequestBody form = formBody.build();
        Request.Builder builder = new Request.Builder();
        Request request = builder.post(form)
                .url(url)
                .build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                callback.failed(e);
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                callback.success(response);
            }
        });
    }
    public interface MyCallback {
        void success(Response res) throws IOException;
        void failed(IOException e);
    }
}

想法有以下几点：

1. 在get()和post()方法中，将需要的参数以HashMap传递键值对，并把相应操作封装。
2. 第二个get()重载是考虑到不需要参数的GET请求的情况。
3. 留下myCallback接口来对不同请求做处理。
4. 由于需要保持cookie来做登录等操作，所以用到了第三方库PersistentCookieJar
5. 考虑到cookie的问题，在不同的activity间需要使用同一个实例才行，有想过使用Intent序列化传递对象，但由于activity太多，传递太繁琐，所以直接写成单例模式。

对于OkHttp的源码还没有深究，有时间再继续研究。

具体使用方法

1. 调用HttpClient.getInstance()获取实例
2. 使用实例调用get和post方法，其中需要传入url，参数(get可以不传)以及MyCallBack回调

只是菜鸡一个..有错还请指正..继续努力学习