需求

更高級的HttpUrlConnection/HttpClient

引入：

maven

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>3.14.2</version>
</dependency>

gradle

compile group: 'com.squareup.okhttp3', name: 'okhttp', version: '3.14.2'

API原理：

1. OkHttpClient負責發送Request，并返回Response:

OkHttpClient client=new OkHttpClient();
Request request=null; //建造者模式建造Request對象
Response response=client.newCall(request).execute();

2. Request對象由建造者模式設置一系列細節：

Request request=new Request.Builder()
                .url("https://www.baidu.com")
                .header("Content-Type","application/json")
                .addHeader("role","admin")
                .addHeader("role","manager")
                .get() //這是默認項
                .build();

3. Response的解析技術綜合：

        Response response=client.newCall(request).execute();
        response.code();//狀態碼
        response.header("Cookie");//響應頭
        response.body().bytes();//原生字節組
        response.body().byteStream();//流方式
        response.body().string();//字符串形式(原始編碼)

異步

//異步調用,開子線程守護網絡響應，且響應結束線程存活
        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                System.out.println("失敗.....");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                System.out.println(response.body().string());
                System.exit(0);
            }
        });
        System.out.println("結局無需等......");

發送請求體（post,put,patch）

1. 使用RequestBody對象：

RequestBody requestBody= RequestBody.create(MediaType,[String|ByteString|byte[]|File])

2. 具體示例（json提交）：

MediaType JSON= MediaType.get("application/json; charset=utf-8");
RequestBody body = RequestBody.create(JSON,"{id:1}");
Request request = new Request.Builder()
      .url(url)
      .post(body)
      .build();

3. 具體示例（普通表單提交）：

RequestBody formBody = new FormBody.Builder()
                .add("name", "john")
                .build();
Request request = new Request.Builder()
                .url("https://en.wikipedia.org/w/index.php")
                .post(formBody)
                .build();

4. 具體示例（文件上傳提交）：

    MediaType MEDIA_TYPE_PNG = MediaType.parse("image/png");
    RequestBody requestBody = new MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("title", "Square Logo")
        .addFormDataPart("image", "logo.png",RequestBody.create(MEDIA_TYPE_PNG,new File("logo.png")))
        .build();

    Request request = new Request.Builder()
        .header("Authorization", "xxxx")
        .url("https://api.imgur.com/3/image")
        .post(requestBody)
        .build();