okhttp边学边记

        学习安卓一定离不开网络访问，但是官方已经不推荐使用HttpClient了，我们需要一个好用的网络库，这时，就想到了okhttp。

一、导包

• 对于Android Studio的用户：compile 'com.squareup.okhttp3:okhttp:(insert latest version)'(目前的最新版本是3.4.1)
• 对于Eclipse的用户：可以直接下载[the lastest JAR],导入项目中即可。
• 注意：官方文档里说到，“当使用到快速I/O和resizable buffers的时候需要okio”所以，还有一步：
  • 对于Android Studio的用户：compile 'com.squareup.okio:okio:(insert latest version)'(目前的最新版本是1.10.0)
  • 对于Eclipse的用户：下载最近的 [ the lastest JAR ] 即可

二、使用步骤：

1. HttpGet

- 首先从最常用到的http get请求开始，例子：
- ```java
    //创建okHttp对象
    OkHttpClient client = new OkHttpClient();
    //创建一个Request
    final Request request = new Request.Builder().url("http://luciferlv.tech").build();
    //new call
    Call call = client.newCall(request);
    //请求加入调度
    call.enqueue(new CallBack(){
            @Override
            public void onFailure(Request request, IOException e){

            }

            @Override
            public void onResponse(final Response response) throws IOException{
                //String htmlStr = response.body().string();
            }
        })
  
- 代码分析：
  1. 发送一个get请求的步骤：首先构造一个Request对象，参数起码有一个url，也可以通过Request.Builder来设置更多的参数如：`header和method`等。
  2. 然后通过request的对象去构造得到一个Call对象，类似于将你的请求封装成了任务，既然是任务，就会有`execute()`和`cancel()`等方法。
  3. 最后，我们希望以**异步**的方式去执行请求，所以我们调用的是`call.enqueue`，将call加入调度队列，然后等待任务执行完成，我们在CallBack中即可得到结果。
  - **注意：**
    - `onResponse`回调的参数是response，一般情况下，比如我们希望获得返回的字符串，可以通过`response.body().string()`获取；如果希望获得返回的二进制字节数组，则调用`response.body().bytes();`如果想拿到返回的inputStream，则调用`response.body().byteStream();`，我们能拿到`inputStream`就可以通过IO的方式下载大文件（写文件）。
    - 还有一个问题`onResponse`执行的线程并不是UI线程。如果希望操作控件，还是需要用到handler等。如：
    - ```java
        @Override
        public void onResponse(final Response response) throws IOException{
            final String res = response.body().string();
            runOnUiThread(new Runnable(){
                @Override
                public void run(){
                    mTextView.setText(res);
                }
            });
        }
    - 我们这里是异步的方式去执行，当然也支持阻塞的方式，上面也说了Call有一个`execute()`方法，你也可以直接调用`call.execute()`通过返回一个`Response`。

2. HttpPost携带参数

- 当请求需要提交参数的时候，我们就会用到post请求，和Get不同的就是Request构造的不同
Request request = buildMultipartFormRequest(url, new File[]{file}, new String[]{fileKey}, null);
FormEncodingBuilder builder = new FormEncodingBuilder();
builder.add("username", "Lucifer");

Request request = new Request.Builder.url(url).post(builder.build()).build();
client.newCall(request).enqueue(new CallBack(){
    @Override
    public void onFailure(Request request, IOException e){

    }

    @Override
    public void onResponse(final Response response) throws IOException{
        //
    }
});
- 大家都清除，post的矢耦，参数是包含在请求体中的；所以我们通过FormEncodingBuilder。添加多个String键值对，然后去构造RequestBody，最后完成我们Request的构造。后面的就和上面的是一样的了。

3. 基于http的文件上传

- 接下来我们再介绍一个可以构造RequestBody的Builder，叫做`MultipartBuilder`。当我们需要做类似与表单上传的时候，就可以用它来构造我们的requestBody。
File file = new File(Environment.getExternalStorageDirectory(), "balabala.mp4");

RequestBody fileBody = RequestBody.create(MediaType.parse("application/octet-stream"), file);

RequestBody requestBody = new MultipartBuilder()
      .type(MultipartBuilder.FORM)
      .addPart(Headers.of("Content-Dispostion", "form-data; name=\"username\""), RequestBody.create(null, "Lucifer"))
      .addPart(Heafers.of("Content-Dispostion", "form-data; name=\"mFile\"; fileName=\"wjd.mp4\""), fileBody)
      .build();

Request request = new Request.Builder()
    .url("http://192.168.1.103:8080/okHttpServer/fileUpload")
    .post(requestBody)
    .build();

Call call = client.newCall(request);
call.enqueue(new CallBack(){
    @Override
    public void onFailure(Request request, IOException e){

    }

    @Override
    public void onResponse(final Response response) throws IOException{
        //
    }
});
- 上述代码向服务器传递了一个键值对`username: Lucifer`和一个文件。我们通过MultipartBuilder的addPart()方法可以添加键值对或者文件。
- 其实类似于我们拼接浏览器行为的方式
- **图片下载：**通过回调的Response拿到byte[]然后decode成图片；
- **文件下载：**通过拿到inputStream做写文件操作。

三、封装

• 由于按照上述的代码，请求多了重复的代码就多了，我们就希望封装这些代码

1. 使用：
2. 一般的get请求

OkHttpClientManager.getAsyn("https://www.baidu.com", new OkHttpClientManager.ResultCallBack<String>(){
    @Override
    public void onError(Request request, Exception e){
        e.printStackTrace();
    }

    @Override
    public void onResponse(String u){
        mTextView.setText(u);//这里是UI线程
    }
});
- 对于一把的请求，我们希望给个url，然后CallBack里面直接操作控件。
2. 文件上传且携带参数
  - 我们希望提供一个方法，传入url, params, file, callback即可。
  
OkHttpClientManager.postAsyn("http://192.168.1.103:8080/okHttpServer/fileUpload", //参数1
    new OkHttpClientManager.ResultCallBack<String>(){
        @Override
        public void onError(Request request, IOException e){
            e.printStackTrace();
        }

        @Override
        public void onResponse(String result){

        }
    },//参数2
    file, //参数3
    "mFile",//参数4
    new OkHttpClientManager.Param[]{
        new OkHttpClientManager.param("username", "lt"),
        new OkHttpClientManager.param("password", "123")
    });
  - 参数3为file，参数4为file对应的name，这个name不是文件的名字；
  - 对应于http中的`<input type="file" name="mFile" >`
  - 对应的是name后面的值，即mFile。
3. 文件下载
  - 对于文件下载，提供url，目标dir，callback即可。
  
OkHttpClientManager.downloadAsyn("http://192.168.1.103:8080/okHttpServer/files/message_01.png",//
    Environment.getExternalStorageDirectory().getAbsolutePath(),//
    new OkHttpClientManager.ResultCallBack<String>(){
        @Override
        public void onError(Request request, IOException e){

        }

        @Override
        public void onResponse(String response){
            //文件下载成功，这里回调的response为文件的absolutePath
        }
    });

4. 展示图片
  - 展示图片，我们希望提供一个url和一个imageView，如果下载成功，直接帮我们设置上即可。
  
OkHttpClientManager.displayImage(mImageView, "http://192.168.1.103:8080/20150817/1.jpg");
  - 内部会自动根据imageView的大小自动对图片进行合适的压缩。虽然，这里可能不适合一次性加载大量图片的场景，但是对于app中偶尔有几个图片的加载，还是可用的。

四、整合Gson

• 项目中使用时，服务端返回的是Json字符串，希望客户端回调可以直接拿到对象，于是整合进入Gson。

1. 直接回调对象

- 例如现在有个User实体类：
public class User{
    public String username;
    public String password;

    public User(){

    }

    public User(String username, String password){
        this.username = username;
        this.password = password;
    }

    @Override
    public String toString(){
        return "User{"+
                "username='" + username + '\'' +
                ",password='" + password + '\'' +
                "}";
    }
}
- 服务端返回：``{"username":"lt", "password":"123"}``
- 客户端可以如下方式的调用：
OkHttpClientManager.getAsyn("http://192.168.56.1:8080/okHttpServer/user!getUser",
    new OkHttpClientManager.ResultCallBack<User>(){
        @Override
        public void onError(Request request, Exception e){
            e.printStackTrace();
        }

        @Override
        public void onResponse(User user){
            mTextView.setText(user.toString());//UI线程
        }
    });
- 我们传入泛型User，在onResponse里面直接回调User对象。
- **注意：**如果在`json字符串->实体对象`过程中发生错误，程序不会崩溃，`onError`方法会被回调。

2. 回调对象集合

- 依然是上述的User类，服务端返回
  - ``[{"username":"lt","password":"123"},{"username":"chl","password":"12345"}]``
- 则客户端可以如下调用：
  - ```java
      OkHttpClientManager.getAsyn("http://192.168.56.1:8080/okHttpServer/user!getUsers",//
          new OkHttpClientManager.ResultCallBack<List<User>>(){
              @Override
              public void onError(Request request, Exception e){
                  e.printStackTrace();
              }

              @Override
              public void onResponse(List<User> us){
                  Log.e("TAG", us.size() + " ");
                  mTextView.setText(us.get(1).toString());
              }
          });
    
      - 唯一的区别，就是泛型变成了`List<User>`。


### OkHttpClientManager的源码
```java
public class OkHttpClientManager
{
    private static OkHttpClientManager mInstance;
    private OkHttpClient mOkHttpClient;
    private Handler mDelivery;
    private Gson mGson;


    private static final String TAG = "OkHttpClientManager";

    private OkHttpClientManager()
    {
        mOkHttpClient = new OkHttpClient();
        //cookie enabled
        mOkHttpClient.setCookieHandler(new CookieManager(null, CookiePolicy.ACCEPT_ORIGINAL_SERVER));
        mDelivery = new Handler(Looper.getMainLooper());
        mGson = new Gson();
    }

    public static OkHttpClientManager getInstance()
    {
        if (mInstance == null)
        {
            synchronized (OkHttpClientManager.class)
            {
                if (mInstance == null)
                {
                    mInstance = new OkHttpClientManager();
                }
            }
        }
        return mInstance;
    }

    /**
     * 同步的Get请求
     *
     * @param url
     * @return Response
     */
    private Response _getAsyn(String url) throws IOException
    {
        final Request request = new Request.Builder()
                .url(url)
                .build();
        Call call = mOkHttpClient.newCall(request);
        Response execute = call.execute();
        return execute;
    }

    /**
     * 同步的Get请求
     *
     * @param url
     * @return 字符串
     */
    private String _getAsString(String url) throws IOException
    {
        Response execute = _getAsyn(url);
        return execute.body().string();
    }


    /**
     * 异步的get请求
     *
     * @param url
     * @param callback
     */
    private void _getAsyn(String url, final ResultCallback callback)
    {
        final Request request = new Request.Builder()
                .url(url)
                .build();
        deliveryResult(callback, request);
    }


    /**
     * 同步的Post请求
     *
     * @param url
     * @param params post的参数
     * @return
     */
    private Response _post(String url, Param... params) throws IOException
    {
        Request request = buildPostRequest(url, params);
        Response response = mOkHttpClient.newCall(request).execute();
        return response;
    }


    /**
     * 同步的Post请求
     *
     * @param url
     * @param params post的参数
     * @return 字符串
     */
    private String _postAsString(String url, Param... params) throws IOException
    {
        Response response = _post(url, params);
        return response.body().string();
    }

    /**
     * 异步的post请求
     *
     * @param url
     * @param callback
     * @param params
     */
    private void _postAsyn(String url, final ResultCallback callback, Param... params)
    {
        Request request = buildPostRequest(url, params);
        deliveryResult(callback, request);
    }

    /**
     * 异步的post请求
     *
     * @param url
     * @param callback
     * @param params
     */
    private void _postAsyn(String url, final ResultCallback callback, Map<String, String> params)
    {
        Param[] paramsArr = map2Params(params);
        Request request = buildPostRequest(url, paramsArr);
        deliveryResult(callback, request);
    }

    /**
     * 同步基于post的文件上传
     *
     * @param params
     * @return
     */
    private Response _post(String url, File[] files, String[] fileKeys, Param... params) throws IOException
    {
        Request request = buildMultipartFormRequest(url, files, fileKeys, params);
        return mOkHttpClient.newCall(request).execute();
    }

    private Response _post(String url, File file, String fileKey) throws IOException
    {
        Request request = buildMultipartFormRequest(url, new File[]{file}, new String[]{fileKey}, null);
        return mOkHttpClient.newCall(request).execute();
    }

    private Response _post(String url, File file, String fileKey, Param... params) throws IOException
    {
        Request request = buildMultipartFormRequest(url, new File[]{file}, new String[]{fileKey}, params);
        return mOkHttpClient.newCall(request).execute();
    }

    /**
     * 异步基于post的文件上传
     *
     * @param url
     * @param callback
     * @param files
     * @param fileKeys
     * @throws IOException
     */
    private void _postAsyn(String url, ResultCallback callback, File[] files, String[] fileKeys, Param... params) throws IOException
    {
        Request request = buildMultipartFormRequest(url, files, fileKeys, params);
        deliveryResult(callback, request);
    }

    /**
     * 异步基于post的文件上传，单文件不带参数上传
     *
     * @param url
     * @param callback
     * @param file
     * @param fileKey
     * @throws IOException
     */
    private void _postAsyn(String url, ResultCallback callback, File file, String fileKey) throws IOException
    {
        Request request = buildMultipartFormRequest(url, new File[]{file}, new String[]{fileKey}, null);
        deliveryResult(callback, request);
    }

    /**
     * 异步基于post的文件上传，单文件且携带其他form参数上传
     *
     * @param url
     * @param callback
     * @param file
     * @param fileKey
     * @param params
     * @throws IOException
     */
    private void _postAsyn(String url, ResultCallback callback, File file, String fileKey, Param... params) throws IOException
    {
        Request request = buildMultipartFormRequest(url, new File[]{file}, new String[]{fileKey}, params);
        deliveryResult(callback, request);
    }

    /**
     * 异步下载文件
     *
     * @param url
     * @param destFileDir 本地文件存储的文件夹
     * @param callback
     */
    private void _downloadAsyn(final String url, final String destFileDir, final ResultCallback callback)
    {
        final Request request = new Request.Builder()
                .url(url)
                .build();
        final Call call = mOkHttpClient.newCall(request);
        call.enqueue(new Callback()
        {
            @Override
            public void onFailure(final Request request, final IOException e)
            {
                sendFailedStringCallback(request, e, callback);
            }

            @Override
            public void onResponse(Response response)
            {
                InputStream is = null;
                byte[] buf = new byte[2048];
                int len = 0;
                FileOutputStream fos = null;
                try
                {
                    is = response.body().byteStream();
                    File file = new File(destFileDir, getFileName(url));
                    fos = new FileOutputStream(file);
                    while ((len = is.read(buf)) != -1)
                    {
                        fos.write(buf, 0, len);
                    }
                    fos.flush();
                    //如果下载文件成功，第一个参数为文件的绝对路径
                    sendSuccessResultCallback(file.getAbsolutePath(), callback);
                } catch (IOException e)
                {
                    sendFailedStringCallback(response.request(), e, callback);
                } finally
                {
                    try
                    {
                        if (is != null) is.close();
                    } catch (IOException e)
                    {
                    }
                    try
                    {
                        if (fos != null) fos.close();
                    } catch (IOException e)
                    {
                    }
                }

            }
        });
    }

    private String getFileName(String path)
    {
        int separatorIndex = path.lastIndexOf("/");
        return (separatorIndex < 0) ? path : path.substring(separatorIndex + 1, path.length());
    }

    /**
     * 加载图片
     *
     * @param view
     * @param url
     * @throws IOException
     */
    private void _displayImage(final ImageView view, final String url, final int errorResId)
    {
        final Request request = new Request.Builder()
                .url(url)
                .build();
        Call call = mOkHttpClient.newCall(request);
        call.enqueue(new Callback()
        {
            @Override
            public void onFailure(Request request, IOException e)
            {
                setErrorResId(view, errorResId);
            }

            @Override
            public void onResponse(Response response)
            {
                InputStream is = null;
                try
                {
                    is = response.body().byteStream();
                    ImageUtils.ImageSize actualImageSize = ImageUtils.getImageSize(is);
                    ImageUtils.ImageSize imageViewSize = ImageUtils.getImageViewSize(view);
                    int inSampleSize = ImageUtils.calculateInSampleSize(actualImageSize, imageViewSize);
                    try
                    {
                        is.reset();
                    } catch (IOException e)
                    {
                        response = _getAsyn(url);
                        is = response.body().byteStream();
                    }

                    BitmapFactory.Options ops = new BitmapFactory.Options();
                    ops.inJustDecodeBounds = false;
                    ops.inSampleSize = inSampleSize;
                    final Bitmap bm = BitmapFactory.decodeStream(is, null, ops);
                    mDelivery.post(new Runnable()
                    {
                        @Override
                        public void run()
                        {
                            view.setImageBitmap(bm);
                        }
                    });
                } catch (Exception e)
                {
                    setErrorResId(view, errorResId);

                } finally
                {
                    if (is != null) try
                    {
                        is.close();
                    } catch (IOException e)
                    {
                        e.printStackTrace();
                    }
                }
            }
        });


    }

    private void setErrorResId(final ImageView view, final int errorResId)
    {
        mDelivery.post(new Runnable()
        {
            @Override
            public void run()
            {
                view.setImageResource(errorResId);
            }
        });
    }


    //*************对外公布的方法************


    public static Response getAsyn(String url) throws IOException
    {
        return getInstance()._getAsyn(url);
    }


    public static String getAsString(String url) throws IOException
    {
        return getInstance()._getAsString(url);
    }

    public static void getAsyn(String url, ResultCallback callback)
    {
        getInstance()._getAsyn(url, callback);
    }

    public static Response post(String url, Param... params) throws IOException
    {
        return getInstance()._post(url, params);
    }

    public static String postAsString(String url, Param... params) throws IOException
    {
        return getInstance()._postAsString(url, params);
    }

    public static void postAsyn(String url, final ResultCallback callback, Param... params)
    {
        getInstance()._postAsyn(url, callback, params);
    }


    public static void postAsyn(String url, final ResultCallback callback, Map<String, String> params)
    {
        getInstance()._postAsyn(url, callback, params);
    }


    public static Response post(String url, File[] files, String[] fileKeys, Param... params) throws IOException
    {
        return getInstance()._post(url, files, fileKeys, params);
    }

    public static Response post(String url, File file, String fileKey) throws IOException
    {
        return getInstance()._post(url, file, fileKey);
    }

    public static Response post(String url, File file, String fileKey, Param... params) throws IOException
    {
        return getInstance()._post(url, file, fileKey, params);
    }

    public static void postAsyn(String url, ResultCallback callback, File[] files, String[] fileKeys, Param... params) throws IOException
    {
        getInstance()._postAsyn(url, callback, files, fileKeys, params);
    }


    public static void postAsyn(String url, ResultCallback callback, File file, String fileKey) throws IOException
    {
        getInstance()._postAsyn(url, callback, file, fileKey);
    }


    public static void postAsyn(String url, ResultCallback callback, File file, String fileKey, Param... params) throws IOException
    {
        getInstance()._postAsyn(url, callback, file, fileKey, params);
    }

    public static void displayImage(final ImageView view, String url, int errorResId) throws IOException
    {
        getInstance()._displayImage(view, url, errorResId);
    }


    public static void displayImage(final ImageView view, String url)
    {
        getInstance()._displayImage(view, url, -1);
    }

    public static void downloadAsyn(String url, String destDir, ResultCallback callback)
    {
        getInstance()._downloadAsyn(url, destDir, callback);
    }

    //****************************


    private Request buildMultipartFormRequest(String url, File[] files,
                                              String[] fileKeys, Param[] params)
    {
        params = validateParam(params);

        MultipartBuilder builder = new MultipartBuilder()
                .type(MultipartBuilder.FORM);

        for (Param param : params)
        {
            builder.addPart(Headers.of("Content-Disposition", "form-data; name=\"" + param.key + "\""),
                    RequestBody.create(null, param.value));
        }
        if (files != null)
        {
            RequestBody fileBody = null;
            for (int i = 0; i < files.length; i++)
            {
                File file = files[i];
                String fileName = file.getName();
                fileBody = RequestBody.create(MediaType.parse(guessMimeType(fileName)), file);
                //TODO 根据文件名设置contentType
                builder.addPart(Headers.of("Content-Disposition",
                                "form-data; name=\"" + fileKeys[i] + "\"; filename=\"" + fileName + "\""),
                        fileBody);
            }
        }

        RequestBody requestBody = builder.build();
        return new Request.Builder()
                .url(url)
                .post(requestBody)
                .build();
    }

    private String guessMimeType(String path)
    {
        FileNameMap fileNameMap = URLConnection.getFileNameMap();
        String contentTypeFor = fileNameMap.getContentTypeFor(path);
        if (contentTypeFor == null)
        {
            contentTypeFor = "application/octet-stream";
        }
        return contentTypeFor;
    }


    private Param[] validateParam(Param[] params)
    {
        if (params == null)
            return new Param[0];
        else return params;
    }

    private Param[] map2Params(Map<String, String> params)
    {
        if (params == null) return new Param[0];
        int size = params.size();
        Param[] res = new Param[size];
        Set<Map.Entry<String, String>> entries = params.entrySet();
        int i = 0;
        for (Map.Entry<String, String> entry : entries)
        {
            res[i++] = new Param(entry.getKey(), entry.getValue());
        }
        return res;
    }

    private static final String SESSION_KEY = "Set-Cookie";
    private static final String mSessionKey = "JSESSIONID";

    private Map<String, String> mSessions = new HashMap<String, String>();

    private void deliveryResult(final ResultCallback callback, Request request)
    {
        mOkHttpClient.newCall(request).enqueue(new Callback()
        {
            @Override
            public void onFailure(final Request request, final IOException e)
            {
                sendFailedStringCallback(request, e, callback);
            }

            @Override
            public void onResponse(final Response response)
            {
                try
                {
                    final String string = response.body().string();
                    if (callback.mType == String.class)
                    {
                        sendSuccessResultCallback(string, callback);
                    } else
                    {
                        Object o = mGson.fromJson(string, callback.mType);
                        sendSuccessResultCallback(o, callback);
                    }


                } catch (IOException e)
                {
                    sendFailedStringCallback(response.request(), e, callback);
                } catch (com.google.gson.JsonParseException e)//Json解析的错误
                {
                    sendFailedStringCallback(response.request(), e, callback);
                }

            }
        });
    }

    private void sendFailedStringCallback(final Request request, final Exception e, final ResultCallback callback)
    {
        mDelivery.post(new Runnable()
        {
            @Override
            public void run()
            {
                if (callback != null)
                    callback.onError(request, e);
            }
        });
    }

    private void sendSuccessResultCallback(final Object object, final ResultCallback callback)
    {
        mDelivery.post(new Runnable()
        {
            @Override
            public void run()
            {
                if (callback != null)
                {
                    callback.onResponse(object);
                }
            }
        });
    }

    private Request buildPostRequest(String url, Param[] params)
    {
        if (params == null)
        {
            params = new Param[0];
        }
        FormEncodingBuilder builder = new FormEncodingBuilder();
        for (Param param : params)
        {
            builder.add(param.key, param.value);
        }
        RequestBody requestBody = builder.build();
        return new Request.Builder()
                .url(url)
                .post(requestBody)
                .build();
    }


    public static abstract class ResultCallback<T>
    {
        Type mType;

        public ResultCallback()
        {
            mType = getSuperclassTypeParameter(getClass());
        }

        static Type getSuperclassTypeParameter(Class<?> subclass)
        {
            Type superclass = subclass.getGenericSuperclass();
            if (superclass instanceof Class)
            {
                throw new RuntimeException("Missing type parameter.");
            }
            ParameterizedType parameterized = (ParameterizedType) superclass;
            return $Gson$Types.canonicalize(parameterized.getActualTypeArguments()[0]);
        }

        public abstract void onError(Request request, Exception e);

        public abstract void onResponse(T response);
    }

    public static class Param
    {
        public Param()
        {
        }

        public Param(String key, String value)
        {
            this.key = key;
            this.value = value;
        }

        String key;
        String value;
    }


}

---

参考文献：

• [okhttp官方文档]
• [ 张鸿洋的博客——从原理角度解析Android （Java） http 文件上传 ]
• [Android OkHttp完全解析]
• [OkHttp官方API文档]
• https://github.com/square/okhttp/
• https://github.com/hongyangAndroid/okhttp-utils