简介

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

源码：https://github.com/square/okhttp
说明：OkHttp支持Android 2.3及以上版本Android平台,对于Java, JDK1.7及以上。
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。

简单使用

引入maven依赖

<dependency>
   <groupId>com.squareup.okhttp3</groupId>
   <artifactId>okhttp</artifactId>
   <version>4.0.0-RC1</version>
</dependency>

请求方法

同步请求

就是执行请求的操作是阻塞式，直到 HTTP 响应返回。它对应 OKHTTP 中的 execute 方法。

GET请求

    /**
     * 同步get方式请求
     *
     * @param url
     * @return
     * @throws IOException
     */
    public static String doGet(String url) throws IOException {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .build();
        try (Response response = client.newCall(request).execute()) {
            if (response.isSuccessful()) {
                return response.body().string();
            } else {
                throw new IOException("Unexpected code " + response);
            }
        }
    }

POST请求

Json提交参数

/**
     * 同步post方式请求-json提交参数
     *
     * @param url
     * @param json
     * @return
     * @throws IOException
     */
    public static String doPost(String url, final String json) throws IOException {
        OkHttpClient client = new OkHttpClient();
        RequestBody body = RequestBody.create(JSON, json);
        Request request = new Request.Builder()
                .url(url)
                .post(body)
                .build();
        try (Response response = client.newCall(request).execute()) {
            if (response.isSuccessful()) {
                return response.body().string();
            } else {
                throw new IOException("Unexpected code " + response);
            }
        }

    }

form表单提交参数

    /**
     * 同步post方式请求-form表单提交参数
     *
     * @param url
     * @param paramsMap
     * @return
     * @throws IOException
     */
    public static String doPost(String url, Map<String, String> paramsMap) throws IOException {
        OkHttpClient client = new OkHttpClient();
        FormBody.Builder builder = new FormBody.Builder();
        for (String key : paramsMap.keySet()) {
            builder.add(key, paramsMap.get(key));
        }
        RequestBody formBody = builder.build();
        Request request = new Request.Builder()
                .url(url)
                .post(formBody)
                .build();
        try (Response response = client.newCall(request).execute()) {
            if (response.isSuccessful()) {
                return response.body().string();
            } else {
                throw new IOException("Unexpected code " + response);
            }
        }

    }

异步请求

就是类似于非阻塞式的请求，它的执行结果一般都是通过接口回调的方式告知调用者。它对应 OKHTTP 中的 enqueue 方法。

这是异步请求，所以调用enqueue则无需再开启子线程，enqueue方法会自动将网络请求部分放入子线程中执行。enqueue回调方法onResponse与onFailure都执行在子线程中。
注意事项：

• 1. 回调接口的onFailure方法和onResponse执行在子线程。
• 2. Response.code是http响应行中的code，如果访问成功则返回200.这个不是服务器设置的，而是http协议中自带的。res中的code才是服务器设置的。注意二者的区别。
• 3. response.body().string()本质是输入流的读操作，所以它还是网络请求的一部分，所以这行代码必须放在子线程。
• 4. response.body().string()只能调用一次，在第一次时有返回值，第二次再调用时将会返回null。原因是：response.body().string()的本质是输入流的读操作，必须有服务器的输出流的写操作时客户端的读操作才能得到数据。而服务器的写操作只执行一次，所以客户端的读操作也只能执行一次，第二次将返回null。
• 5. 再次强调，response.body().string()方法必须放在子线程中。当执行这行代码得到结果后，再跳转到UI线程修改UI。

异步请求自定义回调函数

/**
     * okhttp 异步调用回调函数
     */
    static class OkHttpCallback implements Callback {
        @Override
        public void onFailure(@NotNull Call call, @NotNull IOException e) {
            log.error(e);
        }

        @Override
        public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
            if (response.isSuccessful()) {
                log.info("Successful data acquisition . . . ");
                log.info("response.code()==" + response.code());
                log.info("response.body().string()==" + response.body().string());
            }
        }
    }

GET请求

    /**
     * 异步get方式请求
     *
     * @param url
     * @return
     * @throws IOException
     */
    public static void doSyncGet(String url) {
        OkHttpClient okHttpClient = new OkHttpClient();
        final Request request = new Request.Builder()
                .url(url)
                .get()
                .build();
        Call call = okHttpClient.newCall(request);
        call.enqueue(new OkHttpCallback());
    }

POST请求

Json提交参数

    /**
     * 异步post方式请求-json提交参数
     *
     * @param url
     * @param json
     * @return
     * @throws IOException
     */
    public static void doSyncPost(String url, final String json) {
        OkHttpClient client = new OkHttpClient();
        RequestBody body = RequestBody.create(JSON, json);
        Request request = new Request.Builder()
                .url(url)
                .post(body)
                .build();
        client.newCall(request).enqueue(new OkHttpCallback());

    }

form表单提交参数

 /**
     * 异步post方式请求-form表单提交参数
     *
     * @param url
     * @param paramsMap
     * @return
     * @throws IOException
     */
    public static void doSyncPost(String url, Map<String, String> paramsMap) {
        OkHttpClient client = new OkHttpClient();
        FormBody.Builder builder = new FormBody.Builder();
        for (String key : paramsMap.keySet()) {
            builder.add(key, paramsMap.get(key));
        }
        RequestBody formBody = builder.build();
        Request request = new Request.Builder()
                .url(url)
                .post(formBody)
                .build();
        client.newCall(request).enqueue(new OkHttpCallback());

    }

参考

• https://www.jianshu.com/p/da4a806e599b
• https://blog.csdn.net/m0_38143863/article/details/80220247

示例代码

package com.ohaotian.feifz.style.study.utils;

import lombok.extern.log4j.Log4j2;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.FormBody;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
import org.jetbrains.annotations.NotNull;

import java.io.IOException;
import java.util.Map;

/**
 * @author feifz
 * @version 1.0.0
 * @Description http工具类，基于okhttp3
 * @createTime 2019年06月06日 09:30:00
 */
@Log4j2
public class HttpUtil {

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


    /**
     * 同步get方式请求
     *
     * @param url
     * @return
     * @throws IOException
     */
    public static String doGet(String url) throws IOException {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .build();
        try (Response response = client.newCall(request).execute()) {
            if (response.isSuccessful()) {
                return response.body().string();
            } else {
                throw new IOException("Unexpected code " + response);
            }
        }
    }

    /**
     * 异步get方式请求
     *
     * @param url
     * @return
     * @throws IOException
     */
    public static void doSyncGet(String url) {
        OkHttpClient okHttpClient = new OkHttpClient();
        final Request request = new Request.Builder()
                .url(url)
                .get()
                .build();
        Call call = okHttpClient.newCall(request);
        call.enqueue(new OkHttpCallback());
    }

    /**
     * 同步post方式请求-json提交参数
     *
     * @param url
     * @param json
     * @return
     * @throws IOException
     */
    public static String doPost(String url, final String json) throws IOException {
        OkHttpClient client = new OkHttpClient();
        RequestBody body = RequestBody.create(JSON, json);
        Request request = new Request.Builder()
                .url(url)
                .post(body)
                .build();
        try (Response response = client.newCall(request).execute()) {
            if (response.isSuccessful()) {
                return response.body().string();
            } else {
                throw new IOException("Unexpected code " + response);
            }
        }

    }

    /**
     * 异步post方式请求-json提交参数
     *
     * @param url
     * @param json
     * @return
     * @throws IOException
     */
    public static void doSyncPost(String url, final String json) {
        OkHttpClient client = new OkHttpClient();
        RequestBody body = RequestBody.create(JSON, json);
        Request request = new Request.Builder()
                .url(url)
                .post(body)
                .build();
        client.newCall(request).enqueue(new OkHttpCallback());

    }

    /**
     * 同步post方式请求-form表单提交参数
     *
     * @param url
     * @param paramsMap
     * @return
     * @throws IOException
     */
    public static String doPost(String url, Map<String, String> paramsMap) throws IOException {
        OkHttpClient client = new OkHttpClient();
        FormBody.Builder builder = new FormBody.Builder();
        for (String key : paramsMap.keySet()) {
            builder.add(key, paramsMap.get(key));
        }
        RequestBody formBody = builder.build();
        Request request = new Request.Builder()
                .url(url)
                .post(formBody)
                .build();
        try (Response response = client.newCall(request).execute()) {
            if (response.isSuccessful()) {
                return response.body().string();
            } else {
                throw new IOException("Unexpected code " + response);
            }
        }

    }

    /**
     * 异步post方式请求-form表单提交参数
     *
     * @param url
     * @param paramsMap
     * @return
     * @throws IOException
     */
    public static void doSyncPost(String url, Map<String, String> paramsMap) {
        OkHttpClient client = new OkHttpClient();
        FormBody.Builder builder = new FormBody.Builder();
        for (String key : paramsMap.keySet()) {
            builder.add(key, paramsMap.get(key));
        }
        RequestBody formBody = builder.build();
        Request request = new Request.Builder()
                .url(url)
                .post(formBody)
                .build();
        client.newCall(request).enqueue(new OkHttpCallback());

    }

    /**
     * okhttp 异步调用回调函数
     */
    static class OkHttpCallback implements Callback {
        @Override
        public void onFailure(@NotNull Call call, @NotNull IOException e) {
            log.error(e);
        }

        @Override
        public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
            if (response.isSuccessful()) {
                log.info("Successful data acquisition . . . ");
                log.info("response.code()==" + response.code());
                log.info("response.body().string()==" + response.body().string());
            }
        }
    }


}

结语

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Http请求-okhttp3基本用法