OkHttp可以说是如今最为流行的网络请求框架之一，今天来探究下OkHttp 的使用方法，包括Get 请求、Post 请求、上传下载文件、上传下载图片等功能

在使用OKHttp之前，首先要先了解如下几个比较核心的类：

• OkHttpClient：客户端对象
• Request：访问请求，Post请求中需要包含RequestBody
• RequestBody：请求数据，在Post请求中用到
• Response：即网络请求的响应结果
• MediaType：数据类型，用来表明数据是json，image，pdf等一系列格式
• client.newCall(request).execute()：同步的请求方法
• client.newCall(request).enqueue(Callback callBack)：异步的请求方法，但Callback是执行在子线程中的，因此不能在此进行UI更新操作

在使用前需要先在项目中添加OkHttp的依赖库，在对应的Module的gradle中添加如下语句

compile 'com.squareup.okhttp3:okhttp:3.6.0'

此外，OkHttp内部依赖另一个开源库OkIo，所以也要将它导入进来

compile 'com.squareup.okio:okio:1.11.0'

然后同步项目即可
OkHttp的GitHub地址是：OkHttp
OkIo的GitHub地址是：OkIo

一、Get 请求

最常见的网络请求方式可以说就是Get请求了，这里来获取我在简书的个人主页的网页内容

public void get(View view) {
        OkHttpClient client = new OkHttpClient();
        //构造Request对象
        //采用建造者模式，链式调用指明进行Get请求,传入Get的请求地址
        Request request = new Request.Builder().get().url("http://www.jianshu.com/u/9df45b87cfdf").build();
        Call call = client.newCall(request);
        //异步调用并设置回调函数
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                ToastUtil.showToast(GetActivity.this, "Get 失败");
            }

            @Override
            public void onResponse(Call call, final Response response) throws IOException {
                final String responseStr = response.body().string();
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tv_result.setText(responseStr);
                    }
                });
            }
        });
    }

需要注意的是，异步调用的回调函数是在子线程当中的，因为需要用Handler或者runOnUiThread来更新UI
这里使用到了一个Toast工具类，用户判断当前线程是否是主线程，是的话则直接弹出Toast，否则利用runOnUiThread来弹出Toast

/**
 * 作者： 叶应是叶
 * 时间： 2017/4/2 15:41
 * 描述：
 */
public class ToastUtil {

    public static void showToast(final Activity activity, final String message) {
        if ("main".equals(Thread.currentThread().getName())) {
            Log.e("ToastUtil", "在主线程");
            Toast.makeText(activity, message, Toast.LENGTH_SHORT).show();
        } else {
            activity.runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Log.e("ToastUtil", "不在主线程");
                    Toast.makeText(activity, message, Toast.LENGTH_SHORT).show();
                }
            });
        }
    }

}

此外，在回调函数的以下方法中

public void onResponse(Call call, final Response response)

如果希望获得返回的是字符串，则可以使用

response.body().string()

如果需要的是字节数组，则使用

response.body().bytes()

如果需要的是输入流，则使用

response.body().byteStream()

二、Post 类型

在OkHttp中用Post方法向服务器发送一个请求体时，请求体需要是一个RequestBody。这个请求体可以是：

• key-value：键值对类型
• String：字符串类型
• Form：类似于Html的表单数据提交
• Stream：流类型
• File：文件类型

三、Post 键值对

 public void postParameter(View view) {
        OkHttpClient client = new OkHttpClient();
        //构建FormBody，传入要提交的参数
        FormBody formBody = new FormBody
                .Builder()
                .add("username", "initObject")
                .add("password", "initObject")
                .build();
        final Request request = new Request.Builder()
                .url("http://www.jianshu.com/")
                .post(formBody)
                .build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                ToastUtil.showToast(PostParameterActivity.this, "Post Parameter 失败");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                final String responseStr = response.body().string();
                ToastUtil.showToast(PostParameterActivity.this, "Code：" + String.valueOf(response.code()));
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tv_result.setText(responseStr);
                    }
                });
            }
        });
    }

这里来向简书的网站主页提交两个参数值，可以通过Post来实现模拟登录的功能。当然这里只是模拟了Post操作而已，提交参数后会跳转到404页面
在

public void onResponse(Call call, Response response)

方法中通过

response.code()

可以得到整数类型的结果码：404

四、Post 字符串

在上面的例子中Post传递的是参数对，有时候我们会有要传送字符串的需要，比如向服务器发送一个JSON字符串。那么就可以用如下方法：

public void postString(View view) {
        OkHttpClient client = new OkHttpClient();
        //RequestBody中的MediaType指定为纯文本，编码方式是utf-8
        RequestBody requestBody = RequestBody.create(MediaType.parse("text/plain;charset=utf-8"),
                "{username:admin;password:admin}");
        final Request request = new Request.Builder()
                .url("http://www.jianshu.com/")
                .post(requestBody)
                .build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                ToastUtil.showToast(PostStringActivity.this, "Post String 失败");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                final String responseStr = response.body().string();
                ToastUtil.showToast(PostStringActivity.this, "Code：" + String.valueOf(response.code()));
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tv_result.setText(responseStr);
                    }
                });
            }
        });
    }

五、Post 表单

通过查看网站登录页的Html源代码，通常都可以查看到如下格式的登录表单

<form id="fm1" action="" method="post">
    <input id="username" name="username" type="text"/>    
    <input id="password" name="password" type="password"/>                    
</form>

这里使用到 MuiltipartBody 来构建一个RequestBody，这是 RequestBody 的一个子类，提交表单数据就是利用这个类来实现的

public void postForm(View view) {
        OkHttpClient client = new OkHttpClient();
        RequestBody requestBody = new MultipartBody.Builder()
                .setType(MultipartBody.FORM)
                .addFormDataPart("username", "叶应是叶")
                .addFormDataPart("password", "叶应是叶")
                .build();
        final Request request = new Request.Builder()
                .url("http://www.jianshu.com/")
                .post(requestBody)
                .build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                ToastUtil.showToast(PostFormActivity.this, "Post Form 失败");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                final String responseStr = response.body().string();
                ToastUtil.showToast(PostFormActivity.this, "Code：" + String.valueOf(response.code()));
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tv_result.setText(responseStr);
                    }
                });
            }
        });
    }

六、Post 流

public void postStreaming(View view) {
        final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("text/x-markdown; charset=utf-8");
        OkHttpClient client = new OkHttpClient();
        RequestBody requestBody = new RequestBody() {
            @Override
            public MediaType contentType() {
                return MEDIA_TYPE_MARKDOWN;
            }

            @Override
            public void writeTo(BufferedSink sink) throws IOException {
                sink.writeUtf8("Numbers\n");
                sink.writeUtf8("-------\n");
                for (int i = 2; i <= 997; i++) {
                    sink.writeUtf8(String.format(" * %s = %s\n", i, factor(i)));
                }
            }

            private String factor(int n) {
                for (int i = 2; i < n; i++) {
                    int x = n / i;
                    if (x * i == n) return factor(x) + " × " + i;
                }
                return Integer.toString(n);
            }
        };
        Request request = new Request.Builder()
                .url("https://api.github.com/markdown/raw")
                .post(requestBody)
                .build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                ToastUtil.showToast(PostStreamingActivity.this, "Post Streaming 失败");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                final String responseStr = response.body().string();
                ToastUtil.showToast(PostStreamingActivity.this, "Code：" + String.valueOf(response.code()));
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tv_result.setText(responseStr);
                    }
                });
            }
        });
    }

七、Post 文件

public void postFile(View view) {
        OkHttpClient client = new OkHttpClient();
        final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("text/x-markdown; charset=utf-8");
        File file = new File("README.md");
        Request request = new Request.Builder()
                .url("https://api.github.com/markdown/raw")
                .post(RequestBody.create(MEDIA_TYPE_MARKDOWN, file))
                .build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                ToastUtil.showToast(PostFileActivity.this, "Post File 失败");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                final String responseStr = response.body().string();
                ToastUtil.showToast(PostFileActivity.this, "Code：" + String.valueOf(response.code()));
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tv_result.setText(responseStr);
                    }
                });
            }
        });
    }

八、下载图片

public void downImage(View view) {
        OkHttpClient client = new OkHttpClient();
        final Request request = new Request
                .Builder()
                .get()
                .url("http://avatar.csdn.net/B/0/1/1_new_one_object.jpg")
                .build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                ToastUtil.showToast(DownImageActivity.this, "下载图片失败");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                InputStream inputStream = response.body().byteStream();
                //将图片显示到ImageView中
                final Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        iv_result.setImageBitmap(bitmap);
                    }
                });
                //将图片保存到本地存储卡中
                File file = new File(Environment.getExternalStorageDirectory(), "image.png");
                FileOutputStream fileOutputStream = new FileOutputStream(file);
                byte[] temp = new byte[128];
                int length;
                while ((length = inputStream.read(temp)) != -1) {
                    fileOutputStream.write(temp, 0, length);
                }
                fileOutputStream.flush();
                fileOutputStream.close();
                inputStream.close();
            }
        });
    }

指定图片地址并下载成功后，获取图片的输入流，先用Bitmap decodeStream(InputStream is)方法将输入流转为Bitmap然后显示出来，然后将图片保存到本地存储卡根目录下
记得要申请存储卡的写权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

九、解析Json

这里来通过Gson将response的内容解析为Java Bean
首先需要先去将Gson.jar文件导入工程

这里来通过OkHttp访问接口“http://news-at.zhihu.com/api/4/themes”，获取Json数据然后将之解析为JavaBean实体

这里写图片描述

首先根据Json格式建立一个JavaBean

/**
 * 作者： 叶应是叶
 * 时间： 2017/4/2 22:27
 * 描述：
 */
public class Bean {

    private String date;

    private List<StoriesBean> stories;

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public List<StoriesBean> getStories() {
        return stories;
    }

    public void setStories(List<StoriesBean> stories) {
        this.stories = stories;
    }

    public static class StoriesBean {

        private int type;

        private int id;

        private String ga_prefix;

        private String title;

        private boolean multipic;

        private List<String> images;

        public int getType() {
            return type;
        }

        public void setType(int type) {
            this.type = type;
        }

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getGa_prefix() {
            return ga_prefix;
        }

        public void setGa_prefix(String ga_prefix) {
            this.ga_prefix = ga_prefix;
        }

        public String getTitle() {
            return title;
        }

        public void setTitle(String title) {
            this.title = title;
        }

        public boolean isMultipic() {
            return multipic;
        }

        public void setMultipic(boolean multipic) {
            this.multipic = multipic;
        }

        public List<String> getImages() {
            return images;
        }

        public void setImages(List<String> images) {
            this.images = images;
        }

        @Override
        public String toString() {
            return "标题='" + title + '\'' + "图片链接=" + images;
        }
    }

}

获取Json数据并解析

public void parseJson(View view) {
        OkHttpClient client = new OkHttpClient();
        final Gson gson = new Gson();
        Request request = new Request.Builder()
                .url("http://news-at.zhihu.com/api/4/news/before/20131119")
                .build();

        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                ToastUtil.showToast(ParseJsonActivity.this, "parse Json 失败");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                ToastUtil.showToast(ParseJsonActivity.this, "Code：" + String.valueOf(response.code()));
                final Bean bean = gson.fromJson(response.body().charStream(), Bean.class);
                List<Bean.StoriesBean> stories = bean.getStories();
                final StringBuilder stringBuilder = new StringBuilder();
                for (Bean.StoriesBean storiesBean : stories) {
                    stringBuilder.append(storiesBean);
                    stringBuilder.append("\n\n\n");
                }
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tv_result.setText(stringBuilder.toString());
                    }
                });
            }
        });
    }

解析结果：

这里写图片描述

这里提供上述示例代码下载：Android OkHttp的基本用法