HTTP是现代应用常用的一种交换数据和媒体的网络方式，高效地使用HTTP能让资源加载更快，节省带宽。OkHttp是一个高效的HTTP客户端，它有以下默认特性：

支持HTTP/2，允许所有同一个主机地址的请求共享同一个socket连接

连接池减少请求延时

透明的GZIP压缩减少响应数据的大小

缓存响应内容，避免一些完全重复的请求

当网络出现问题的时候OkHttp依然坚守自己的职责，它会自动恢复一般的连接问题，如果你的服务有多个IP地址，当第一个IP请求失败时，OkHttp会交替尝试你配置的其他IP，OkHttp使用现代TLS技术(SNI, ALPN)初始化新的连接，当握手失败时会回退到TLS 1.0。

官网原文：

HTTP is the way modern applications network. It’s how we exchange data & media. Doing HTTP efficiently makes your stuff load faster and saves bandwidth.

OkHttp is an HTTP client that’s efficient by default:

HTTP/2 support allows all requests to the same host to share a socket.

Connection pooling reduces request latency (if HTTP/2 isn’t available).

Transparent GZIP shrinks download sizes.

Response caching avoids the network completely for repeat requests.

OkHttp perseveres when the network is troublesome: it will silently recover from common connection problems. If your service has multiple IP addresses OkHttp will attempt alternate addresses if the first connect fails. This is necessary for IPv4+IPv6 and for services hosted in redundant data centers. OkHttp initiates new connections with modern TLS features (SNI, ALPN), and falls back to TLS 1.0 if the handshake fails.

Android 演变：

下载

Gradle1implementation("com.squareup.okhttp3:okhttp:version code")

示例:

1implementation("com.squareup.okhttp3:okhttp:3.12.1")

不建议使用”+”或者latest.release代替版本号，最新的未必是最好的

jar

GET 方法1

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11OkHttpClient client = new OkHttpClient();

String run(String url) throws IOException{

Request request = new Request.Builder()

.url(url)

.build();

try (Response response = client.newCall(request).execute()) {

return response.body().string();

}

}

POST 方法1

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14public static final MediaType JSON = MediaType.get("application/json; charset=utf-8");

OkHttpClient client = new OkHttpClient();

String post(String url, String json) throws IOException{

RequestBody body = RequestBody.create(JSON, json);

Request request = new Request.Builder()

.url(url)

.post(body)

.build();

try (Response response = client.newCall(request).execute()) {

return response.body().string();

}

}

以上两个demo来自OkHttp官网op1=>operation: Android2.3之前基于HttpClient

op2=>operation: Android2.3之后基于HttpURLConnection

op3=>operation: Android4.4之后基于okhttp

op4=>operation: Android6.0移除org.apache.http.*只保留了个别类

op1->op2->op3->op4{"scale":1,"line-width":2,"line-length":50,"text-margin":10,"font-size":12}