网络请求库OkHttp的使用

OkHttp是一个开源的Java的http网络请求库，常用于安卓的APP的网络请求。

1. 第一步当然要导入jar包，由于OKhttp依赖okio,必须同时导入，这里可通过

    compile 'com.squareup.okhttp3:okhttp:3.4.1'
    compile 'com.squareup.okio:okio:1.9.0'

直接导入，或在官网下载jar包手动导入。

2. 构建OkHttpClient对象
   一般可直接通过client = new OkHttpClient();即可，如需使用cache则要

        // 设置缓存目录与缓存大小上限
        Cache cache = new Cache(new File("okHttpCache"), 1024 * 1000);
        // okhttp3不再以setCache设置缓存而是通过OkHttpClient.Builder来设置了
        OkHttpClient.Builder clientBuilder = new OkHttpClient.Builder();
        clientBuilder.cache(cache);
        // 构建客户端对象
        OkHttpClient = clientBuilder.build();

3. 使用OKhttp进行GET请求；
   封装Request对象

        Request request = new Request.Builder()
                .url(url)
                .build();

阻塞式请求，通过client获取request的Response对象

        Response response = client.newCall(request).execute();      //阻塞

需要注意的是调用.execute()方法会阻塞当前线程，会一直阻塞到请求完成。
请求结果已经封装在response对象内。

        if (response.isSuccessful()) {
            String content = response.body().string();
            System.out.println(content);
        }

异步请求：
异步请求可直接通过client获取

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                e.printStackTrace();
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                System.out.println("call = [" + call + "], response = [" + response + "]");
                System.out.println();
                if (!response.isSuccessful()) {
                    throw new IOException("" + response);
                }

                Headers headers = response.headers();
                for (int i = 0; i < headers.size(); i++) {
                    System.out.println(headers.name(i) + ": " + headers.value(i));
                }

                System.out.println();
                System.out.println(response.body().string());
            }
        });

4. 使用OKhttp进行application/x-www-form-urlencoded方式POST请求
   封装请求参数

        RequestBody formBody = new FormBody.Builder()
                .add("param0", "lt")
                .add("param1", "lt2")
                .build();

阻塞式post请求：

        Request request = new Request.Builder().url(url).post(formBody).build();
        Response response = client.newCall(request).execute();

        if (response.isSuccessful()) {
            System.out.println(response.body().string());
        }

非阻塞式，跟get使用方式相似，如下

        Request request = new Request.Builder().url(url).post(formBody).build();
        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                System.out.println(e.getMessage());
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                System.out.println("非阻塞请求 \n" + response.body().string());
            }
        });

使用OKhttp进行application/json方式POST请求
封装请求参数同上

        RequestBody formBody = new FormBody.Builder()
                .add("param0", "lt")
                .add("param1", "lt2")
                .build();

设置MediaType

MediaType mediaType = MediaType.parse("application/json; charset=utf-8")

通过mediatype和json格式的请求参数来获取RequestBody

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

然后同上直接请求即可

        Request request = new Request.Builder().url(url).post(body).build();
        Response response = client.newCall(request).execute();

总的来说，就是先封装Request对象，再通过client获取Response或异步处理，POST则需额外的请求参数RequestBody和MediaType的封装。

完整测试代码

package xyz.liut.net.http.okhttp;

import java.io.File;
import java.io.IOException;

import okhttp3.Cache;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.FormBody;
import okhttp3.Headers;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

/**
 * OkHttp test
 * Created by liut_ on 2016/10/25.
 */

public class OkHttpTest {

    public static final String URL = "http://localhost:8080/WebTest/servlet";
    public static final MediaType mediaType = MediaType.parse("application/json; charset=utf-8");
//    public static final MediaType mediaType = MediaType.parse("application/x-www-form-urlencoded; charset=utf-8");

    private OkHttpClient client;

    private OkHttpTest() {

        // 设置缓存目录与缓存大小上限
        Cache cache = new Cache(new File("okHttpCache"), 1024 * 1000);
        // okhttp3不再以setCache设置缓存而是通过OkHttpClient.Builder来设置了
        OkHttpClient.Builder clientBuilder = new OkHttpClient.Builder();
        clientBuilder.cache(cache);
        // 构建客户端对象
        client = clientBuilder.build();

//        client.dispatcher().cancelAll(); // 可以取消全部请求

//        client = new OkHttpClient();      //不用缓存

    }

    void doGet(String url) throws IOException {
        Request request = new Request.Builder()
                .url(url)
                .build();
//        Response response = client.newCall(request).execute();      //阻塞

//        if (response.isSuccessful()) {
//            String content = response.body().string();
//            System.out.println(content);
//        }


        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                e.printStackTrace();
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                System.out.println("call = [" + call + "], response = [" + response + "]");
                System.out.println();
                if (!response.isSuccessful()) {
                    throw new IOException("" + response);
                }

                Headers headers = response.headers();
                for (int i = 0; i < headers.size(); i++) {
                    System.out.println(headers.name(i) + ": " + headers.value(i));
                }

                System.out.println();
                System.out.println(response.body().string());
            }
        });

    }


    /**
     * 通过application/json方式post
     *
     * @param url  url
     * @param json params
     * @throws IOException
     */
    void doPostByJson(String url, String json) throws IOException {
        RequestBody body = RequestBody.create(mediaType, json);

        Request request = new Request.Builder().url(url).post(body).build();
        Response response = client.newCall(request).execute();

        if (response.isSuccessful()) {
            System.out.println(response.body().string());
        }
    }

    /**
     * 通过application/x-www-form-urlencoded
     *
     * @param url url
     * @throws IOException
     */
    void doPostByFormData(String url) throws IOException {
        RequestBody formBody = new FormBody.Builder()
                .add("param0", "lt")
                .add("param1", "lt2")
                .build();

        Request request = new Request.Builder().url(url).post(formBody).build();
//        Response response = client.newCall(request).execute();
//
//        if (response.isSuccessful()) {
//            System.out.println(response.body().string());
//        }

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                System.out.println(e.getMessage());
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                System.out.println("非阻塞请求 \n" + response.body().string());
            }
        });

    }


    public static void main(String[] args) throws IOException {
        OkHttpTest test = new OkHttpTest();

        test.doGet(URL + "?" + "param0=woca&param1=nihao");
        test.doPostByJson(URL, "{\"param0\":\"hehe\"}");
        test.doPostByFormData(URL);
    }

}