一、pom.xml

        <dependency>
            <groupId>com.squareup.okhttp3</groupId>
            <artifactId>okhttp</artifactId>
            <version>4.8.1</version>
        </dependency>

        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib</artifactId>
            <version>1.3.70</version>
        </dependency>

二、GET请求

1、普通get请求。

        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .build();
        try {
            Response response = client.newCall(request).execute();
            System.out.println(response.body().string());
        } catch (IOException e) {
	    e.printStackTrace();
        }

2、添加请求头参数

        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .addHeader("client_id", "123")
                .addHeader("sign", "123")
                .addHeader("sign_method", "123")
                .addHeader("t", "123")
                .build();
        try {
            Response response = client.newCall(request).execute();
            System.out.println(response.body().string());
        } catch (IOException e) {
	e.printStackTrace();
        }

三、POST请求

1、表单POST请求

        OkHttpClient client = new OkHttpClient();

        // 提交FormData
        FormBody.Builder form = new FormBody.Builder();
        form.add("name", "Tom");
        form.add("age", "23");

        Request request = new Request.Builder()
                .url("http://httpbin.org/post")
                .post(form.build())
                .build();

        Response response = client.newCall(request).execute();
        System.out.println(response.body().string());

2、JSON提交

        public static final MediaType JSON = MediaType.parse("application/json; charset=utf-8");

        OkHttpClient client = new OkHttpClient();

        Map<String, Object> map = new HashMap<>();
        map.put("name", "Tom");
        map.put("age", 23);

        Gson gson = new Gson();
        String data = gson.toJson(map);

        RequestBody requestBody = RequestBody.create(data, JSON);

        Request request = new Request.Builder()
                .url("http://httpbin.org/post")
                .post(requestBody)
                .build();

        Response response = client.newCall(request).execute();
        System.out.println(response.body().string()); 

已在真实项目中运行。

参考demo：

https://blog.csdn.net/mouday/article/details/108253164

https://www.cnblogs.com/lxlw/p/11767888.html