OkHttp 的使用与跳坑示例

三月 22, 2020 JavaEE/Web

OkHttp 是一个优秀的网络请求框架，我开始接触 Android 开发的时候就用过这个网络请求框架，官方的参考文档在这里 https://square.github.io/okhttp/ ，本文演示了使用 OkHttp 框架进行简单的 Get、Post（表单形式和 JSON 形式）、Delete、附加请求头、请求异步回调，文件的上传和下载等常用操作。最后记录了一个今天调试了很久的坑，那就是 response.body ().string () 只能有效调用一次，注意 Debug 的时候对结果造成的改变！JDK9 的 HttpURLConnection 有很多变化，下次博客中会有演示和说明。

首选引入这个依赖就可以使用 OkHTTP 了

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>3.6.0</version>
</dependency>

<!-- 这个是我演示 Post 请求 JSON 格式的时候用到的 -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.47</version>
</dependency>

如果是 gradle 管理的项目，则只需要引入：

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

1、Get 请求示例

String url = "http://zouchanglin.cn";
OkHttpClient okHttpClient = new OkHttpClient();
Request request = new Request.Builder ().get ().url (url).build ();
try {
    Response execute = okHttpClient.newCall (request).execute ();
    System.out.println (execute.body ().string ());
} catch (IOException e) {
    e.printStackTrace ();
}

2、Post 请求示例

1、JSON 请求

public static void main(String [] args) {
    String url = "http://zouchanglin.cn/info/create";
    OkHttpClient okHttpClient = new OkHttpClient();
    Map<String, Object> map = new HashMap<>();
    map.put ("name", "Mike");
    map.put ("age", "20");
    RequestBody requestBody = RequestBody.create (
        MediaType.parse ("application/json; charset=utf-8"),
        JSONObject.toJSONString (map));
    Request request = new Request.Builder ().post (requestBody).url (url).build ();
    try {
        Response response = okHttpClient.newCall (request).execute ();
        System.out.println (response.body ().string ());
    } catch (IOException e) {
        e.printStackTrace ();
    }
}

2、表单数据

public static void main(String [] args) {
    String url = "http://zouchanglin.cn/info/create";
    OkHttpClient okHttpClient = new OkHttpClient();
    RequestBody requestBody = new FormBody.Builder ()
        .add ("name", "Mike")
        .add ("age", "20").build ();
    Request request = new Request.Builder ().post (requestBody).url (url).build ();
    try {
        Response response = okHttpClient.newCall (request).execute ();
        System.out.println (response.body ().string ());
    } catch (IOException e) {
        e.printStackTrace ();
    }
}

3、Delete 请求示例

public static void main(String [] args) {
    String url = "http://zouchanglin.cn/info/remove";
    OkHttpClient okHttpClient = new OkHttpClient();
    RequestBody requestBody = new FormBody.Builder ()
        .add ("id", "001002003004").build ();
    Request request = new Request.Builder ()
        .delete (requestBody).url (url).build ();
    try {
        Response response = okHttpClient.newCall (request).execute ();
        System.out.println (response.body ().string ());
    } catch (IOException e) {
        e.printStackTrace ();
    }
}

4、附加请求头示例

public static void main(String [] args) {
    String url = "http://zouchanglin.cn/info/remove";
    OkHttpClient okHttpClient = new OkHttpClient();
    RequestBody requestBody = new FormBody.Builder ()
        .add ("id", "001002003004").build ();
    Request request = new Request.Builder ()
        .delete (requestBody)
        .addHeader ("Accept", "application/vnd..")
        .url (url).build ();
    try {
        Response response = okHttpClient.newCall (request).execute ();
        System.out.println (response.body ().string ());
    } catch (IOException e) {
        e.printStackTrace ();
    }
}

5、请求异步回调示例

public static void main(String [] args) {
    String url = "http://zouchanglin.cn/info/remove";
    OkHttpClient okHttpClient = new OkHttpClient();
    RequestBody requestBody = new FormBody.Builder ()
        .add ("id", "0010003004").build ();
    Request request = new Request.Builder ().delete (requestBody).url (url).build ();
    Call call = okHttpClient.newCall (request);
    call.enqueue (new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            //TODO...
        }

        @Override
        public void onResponse(Call call, Response response) throws IOException {
            //TODO...
        }
    });
}

6、上传文件加参数示例

@PostMapping ("upload")
public String uploadToRemoteHost(String ip, String path, String fileId) {
    String url = String.format ("http://% s:8080//api/host/file/create/", ip);
    // 找到文件对象 
    Optional<ImageFile> bigFileById = fileService.getBigFileById (fileId);
    if(bigFileById.isPresent ()){
        ImageFile imageFile = bigFileById.get ();
        OkHttpClient okHttpClient = new OkHttpClient();
        MultipartBody.Builder requestBody = new MultipartBody.Builder ();
        requestBody.setType (MultipartBody.FORM);
        RequestBody body = RequestBody.create (
            MediaType.parse ("application/octet-stream"), 
            imageFile.getContent ().getData ());
        
        // 参数分别为 请求 key 文件名称 RequestBody
        requestBody.addFormDataPart ("file", imageFile.getName (), body);
        // 要上传的文字参数 
        Map<String, String> map = new HashMap<>();
        map.put ("name", imageFile.getName ());
        map.put ("path", path);
        for (String key : map.keySet ()) {
            requestBody.addFormDataPart (key, map.get (key));
        }
        MultipartBody build = requestBody.build ();
        try {
            Request request = new Request.Builder ().post (build).url (url).build ();
            Response execute = okHttpClient.newCall (request).execute ();
            if(execute.isSuccessful ()){
                return execute.body ().string ();
            }
            return JSONObject.toJSONString (ResultVOUtil.error (1, " 网络错误 & quot;));
        } catch (IOException e) {
            e.printStackTrace ();
            return JSONObject.toJSONString (ResultVOUtil.error (2, " 网络错误 2"));
        }
    }
    return JSONObject.toJSONString (ResultVOUtil.error (3, " 文件不存在 & quot;));
}

7、下载文件示例

public void downloadImg(View view){
    OkHttpClient client = new OkHttpClient();
    final Request request = new Request.Builder ().get ()
            .url ("http://wwwx.yyy/a.png")
            .build ();
    Call call = client.newCall (request);
    call.enqueue (new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            Log.e ("moer", "onFailure: ");;
        }

        @Override
        public void onResponse(Call call, Response response) throws IOException {
            // 拿到字节流 
            InputStream is = response.body ().byteStream ();

            int len = 0;
            File file  = new File(Environment.getExternalStorageDirectory (), "n.png");
            FileOutputStream fos = new FileOutputStream(file);
            byte[] buf = new byte[128];

            while ((len = is.read (buf)) != -1){
                fos.write (buf, 0, len);
            }

            fos.flush ();
            // 关闭流 
            fos.close ();
            is.close ();
        }
    });
}

8、OkHttp 的坑

OkHttp 请求回调中 response.body ().string () 只能有效调用一次，调用 response.body ().string () 的时候数据流已经关闭了，再次调用就是提示已经 closed，抛出 java.lang.IllegalStateException: closed 异常，所以这个坑还是有点大，我在 debug 的时候由于已经监视了一次 response.body ().string () 的返回值，在代码中跑完就是 IllegalStateException。调试代码调试时，表达式的监视有时候会影响代码的运行，比如就像 OkHttp 这种情况。