OkHttp使用教程

痛定思痛。 2022-08-22 04:42 210阅读 0赞

Android系统提供了两种HTTP通信类，HttpURLConnection和HttpClient。  
关于HttpURLConnection和HttpClient的选择>>官方博客  
尽管Google在大部分安卓版本中推荐使用HttpURLConnection，但是这个类相比HttpClient实在是太难用，太弱爆了。  
OkHttp是一个相对成熟的解决方案，据说Android4.4的源码中可以看到HttpURLConnection已经替换成OkHttp实现了。所以我们更有理由相信OkHttp的强大。

OkHttp 处理了很多网络疑难杂症：会从很多常用的连接问题中自动恢复。如果您的服务器配置了多个IP地址，当第一个IP连接失败的时候，OkHttp会自动尝试下一个IP。OkHttp还处理了代理服务器问题和SSL握手失败问题。

使用 OkHttp 无需重写您程序中的网络代码。OkHttp实现了几乎和java.net.HttpURLConnection一样的API。如果你用了 Apache HttpClient，则OkHttp也提供了一个对应的okhttp-apache 模块。

使用范围  
OkHttp支持Android 2.3及其以上版本。  
对于Java, JDK1.7以上。

jar包准备  
官方介绍页面有链接位置。这里把下载链接也写在下面。  
OkHttp  
Okio

**基本使用**  
HTTP GET

OkHttpClient client = new OkHttpClient();
    
    String run(String url) throws IOException {
    
        Request request = new Request.Builder().url(url).build();
    
        Response response = client.newCall(request).execute();    
        if (response.isSuccessful()) {
          return response.body().string();
        } else {
        throw new IOException("Unexpected code " + response);
        }
    
    }

Request是OkHttp中访问的请求，Builder是辅助类。Response即OkHttp中的响应

**Response类：**

public boolean isSuccessful()
    
    Returns true if the code is in [200..300),
    
     which means the request was successfully received, understood, and accepted.

**response.body()返回ResponseBody类**  
可以方便的获取string  
public final String string() throws IOException

Returns the response as a string decoded with the charset of the Content-Type header. If that header is either absent or lacks a charset,

this will attempt to decode the response body as UTF-8.Throws:

IOException

当然也能获取到流的形式：

public final InputStream byteStream()

**HTTP POST**  
**POST提交Json数据**

public static final MediaType JSON = MediaType.parse("application/json; charset=utf-8");
    
    OkHttpClient client = new OkHttpClient();
    
    String post(String url, String json) throws IOException {
    
         RequestBody body = RequestBody.create(JSON, json);
    
          Request request = new Request.Builder()
    
          .url(url)
    
          .post(body)
    
          .build();
    
          Response response = client.newCall(request).execute();
    
        f (response.isSuccessful()) {
    
            return response.body().string();
    
        } else {
    
            throw new IOException("Unexpected code " + response);
    
        }
    
    }

使用Request的post方法来提交请求体RequestBody

**POST提交键值对**  
很多时候我们会需要通过POST方式把键值对数据传送到服务器。 OkHttp提供了很方便的方式来做这件事情。

OkHttpClient client = new OkHttpClient();
    
    String post(String url, String json) throws IOException {
    
    
    
         RequestBody formBody = new FormEncodingBuilder()
    
        .add("platform", "android")
    
        .add("name", "bug")
    
        .add("subject", "XXXXXXXXXXXXXXX")
    
        .build();
    
    
    
          Request request = new Request.Builder()
    
          .url(url)
    
          .post(body)
    
          .build();
    
    
    
          Response response = client.newCall(request).execute();
    
        if (response.isSuccessful()) {
    
            return response.body().string();
    
        } else {
    
            throw new IOException("Unexpected code " + response);
    
        }
    
    }

**总结**

通过上面的例子我们可以发现，OkHttp在很多时候使用都是很方便的，而且很多代码也有重复，因此特地整理了下面的工具类。  
注意：

OkHttp官方文档并不建议我们创建多个OkHttpClient，因此全局使用一个。 如果有需要，可以使用clone方法，再进行自定义。这点在后面的高级教程里会提到。  
enqueue为OkHttp提供的异步方法，入门教程中并没有提到，后面的高级教程里会有解释。

import java.io.IOException;
    
    import java.util.List;
    
    import java.util.concurrent.TimeUnit;
    
    import org.apache.http.client.utils.URLEncodedUtils;
    
    import org.apache.http.message.BasicNameValuePair;
    
    import cn.wiz.sdk.constant.WizConstant;
    
    import com.squareup.okhttp.Callback;
    
    import com.squareup.okhttp.OkHttpClient;
    
    import com.squareup.okhttp.Request;
    
    import com.squareup.okhttp.Response; 
    
    
    
    public class OkHttpUtil { 
    
        private static final OkHttpClient mOkHttpClient = new OkHttpClient();
    
        static{
    
            mOkHttpClient.setConnectTimeout(30, TimeUnit.SECONDS);
    
        }
    
        /** * 该不会开启异步线程。 * @param request * @return * @throws IOException */
    
        public static Response execute(Request request) throws IOException{
    
            return mOkHttpClient.newCall(request).execute();
    
        }
    
        /** * 开启异步线程访问网络 * @param request * @param responseCallback */
    
        public static void enqueue(Request request, Callback responseCallback){
    
            mOkHttpClient.newCall(request).enqueue(responseCallback);
    
        }
    
        /** * 开启异步线程访问网络, 且不在意返回结果（实现空callback） * @param request */
    
        public static void enqueue(Request request){
    
            mOkHttpClient.newCall(request).enqueue(new Callback() {
    
    
    
                @Override
    
                public void onResponse(Response arg0) throws IOException {
    
    
    
                }
    
    
    
                @Override
    
                public void onFailure(Request arg0, IOException arg1) {
    
    
    
                }
    
            });
    
        }
    
        public static String getStringFromServer(String url) throws IOException{
    
            Request request = new Request.Builder().url(url).build();
    
            Response response = execute(request);
    
            if (response.isSuccessful()) {
    
                String responseUrl = response.body().string();
    
                return responseUrl;
    
            } else {
    
                throw new IOException("Unexpected code " + response);
    
            }
    
        }
    
        private static final String CHARSET_NAME = "UTF-8";
    
        /** * 这里使用了HttpClinet的API。只是为了方便 * @param params * @return */
    
        public static String formatParams(List<BasicNameValuePair> params){
    
            return URLEncodedUtils.format(params, CHARSET_NAME);
    
        }
    
        /** * 为HttpGet 的 url 方便的添加多个name value 参数。 * @param url * @param params * @return */
    
        public static String attachHttpGetParams(String url, List<BasicNameValuePair> params){
    
            return url + "?" + formatParams(params);
    
        }
    
        /** * 为HttpGet 的 url 方便的添加1个name value 参数。 * @param url * @param name * @param value * @return */
    
        public static String attachHttpGetParam(String url, String name, String value){
    
            return url + "?" + name + "=" + value;
    
        }
    
    }

**高级**  
高级属性其实用的不多，这里主要是对OkHttp github官方教程进行了翻译。  
**同步get**  
下载一个文件，打印他的响应头，以string形式打印响应体。  
响应体的 string() 方法对于小文档来说十分方便、高效。但是如果响应体太大（超过1MB），应避免适应 string()方法 ，因为他会将把整个文档加载到内存中。  
对于超过1MB的响应body，应使用流的方式来处理body。

private final OkHttpClient client = new OkHttpClient();
    
    
    
    public void run() throws Exception {
    
        Request request = new Request.Builder()
    
            .url("http://publicobject.com/helloworld.txt")
    
            .build();
    
    
    
        Response response = client.newCall(request).execute();
    
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
        Headers responseHeaders = response.headers();
    
        for (int i = 0; i < responseHeaders.size(); i++) {
    
          System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
    
        }
    
    
    
        System.out.println(response.body().string());
    
    }

**异步get**  
在一个工作线程中下载文件，当响应可读时回调Callback接口。读取响应时会阻塞当前线程。OkHttp现阶段不提供异步api来接收响应体。

private final OkHttpClient client = new OkHttpClient();
    
    
    
    public void run() throws Exception {
    
        Request request = new Request.Builder()
    
            .url("http://publicobject.com/helloworld.txt")
    
            .build();
    
    
    
        client.newCall(request).enqueue(new Callback() {
    
          @Override public void onFailure(Request request, Throwable throwable) {
    
            throwable.printStackTrace();
    
          }
    
    
    
          @Override public void onResponse(Response response) throws IOException {
    
            if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
            Headers responseHeaders = response.headers();
    
            for (int i = 0; i < responseHeaders.size(); i++) {
    
              System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
    
            }
    
    
    
            System.out.println(response.body().string());
    
          }
    
        });
    
    }

**提取响应头**  
典型的HTTP头 像是一个 Map

private final OkHttpClient client = new OkHttpClient();
    
    
    
    public void run() throws Exception {
    
        Request request = new Request.Builder()
    
            .url("https://api.github.com/repos/square/okhttp/issues")
    
            .header("User-Agent", "OkHttp Headers.java")
    
            .addHeader("Accept", "application/json; q=0.5")
    
            .addHeader("Accept", "application/vnd.github.v3+json")
    
            .build();
    
    
    
        Response response = client.newCall(request).execute();
    
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
        System.out.println("Server: " + response.header("Server"));
    
        System.out.println("Date: " + response.header("Date"));
    
        System.out.println("Vary: " + response.headers("Vary"));
    
    }

**Post方式提交String**  
使用HTTP POST提交请求到服务。这个例子提交了一个markdown文档到web服务，以HTML方式渲染markdown。因为整个请求体都在内存中，因此避免使用此

public static final MediaType MEDIA_TYPE_MARKDOWN
    
      = MediaType.parse("text/x-markdown; charset=utf-8");
    
    
    
    private final OkHttpClient client = new OkHttpClient();
    
    
    
    public void run() throws Exception {
    
        String postBody = ""
    
            + "Releases\n"
    
            + "--------\n"
    
            + "\n"
    
            + " * _1.0_ May 6, 2013\n"
    
            + " * _1.1_ June 15, 2013\n"
    
            + " * _1.2_ August 11, 2013\n";
    
    
    
        Request request = new Request.Builder()
    
            .url("https://api.github.com/markdown/raw")
    
            .post(RequestBody.create(MEDIA_TYPE_MARKDOWN, postBody))
    
            .build();
    
    
    
        Response response = client.newCall(request).execute();
    
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
        System.out.println(response.body().string());
    
    }

**Post方式提交流**  
以流的方式POST提交请求体。请求体的内容由流写入产生。这个例子是流直接写入Okio的BufferedSink。你的程序可能会使用OutputStream，你可以使用BufferedSink.outputStream()来获取

public static final MediaType MEDIA_TYPE_MARKDOWN
    
          = MediaType.parse("text/x-markdown; charset=utf-8");
    
    
    
    private final OkHttpClient client = new OkHttpClient();
    
    
    
    public void run() throws Exception {
    
        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();
    
    
    
        Response response = client.newCall(request).execute();
    
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
        System.out.println(response.body().string());
    
    }

**Post方式提交文件**  
以文件作为请求体是十分简单的。

public static final MediaType MEDIA_TYPE_MARKDOWN
    
      = MediaType.parse("text/x-markdown; charset=utf-8");
    
    
    
    private final OkHttpClient client = new OkHttpClient();
    
    
    
    public void run() throws Exception {
    
        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();
    
    
    
        Response response = client.newCall(request).execute();
    
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
        System.out.println(response.body().string());
    
    }

**Post方式提交表单**  
使用FormEncodingBuilder来构建和HTML标签相同效果的请求体。键值对将使用一种HTML兼容形式的URL编码来进行编码。

private final OkHttpClient client = new OkHttpClient();
    
    
    
    public void run() throws Exception {
    
        RequestBody formBody = new FormEncodingBuilder()
    
            .add("search", "Jurassic Park")
    
            .build();
    
        Request request = new Request.Builder()
    
            .url("https://en.wikipedia.org/w/index.php")
    
            .post(formBody)
    
            .build();
    
    
    
        Response response = client.newCall(request).execute();
    
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
        System.out.println(response.body().string());
    
    }

**Post方式提交分块请求**  
MultipartBuilder可以构建复杂的请求体，与HTML文件上传形式兼容。多块请求体中每块请求都是一个请求体，可以定义自己的请求头。这些请求头可以用来描述这块请求，例如他的Content-Disposition。如果Content-Length和Content-Type可用的话，他们会被自动添加到请求头中。

private static final String IMGUR_CLIENT_ID = "...";
    
    private static final MediaType MEDIA_TYPE_PNG = MediaType.parse("image/png");
    
    
    
    private final OkHttpClient client = new OkHttpClient();
    
    
    
    public void run() throws Exception {
    
        // Use the imgur image upload API as documented at https://api.imgur.com/endpoints/image
    
        RequestBody requestBody = new MultipartBuilder()
    
            .type(MultipartBuilder.FORM)
    
            .addPart(
    
                Headers.of("Content-Disposition", "form-data; name=\"title\""),
    
                RequestBody.create(null, "Square Logo"))
    
            .addPart(
    
                Headers.of("Content-Disposition", "form-data; name=\"image\""),
    
                RequestBody.create(MEDIA_TYPE_PNG, new File("website/static/logo-square.png")))
    
            .build();
    
    
    
        Request request = new Request.Builder()
    
            .header("Authorization", "Client-ID " + IMGUR_CLIENT_ID)
    
            .url("https://api.imgur.com/3/image")
    
            .post(requestBody)
    
            .build();
    
    
    
        Response response = client.newCall(request).execute();
    
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
        System.out.println(response.body().string());
    
    }

**使用Gson来解析JSON响应**  
Gson是一个在JSON和Java对象之间转换非常方便的api。这里我们用Gson来解析Github API的JSON响应。  
注意：ResponseBody.charStream()使用响应头Content-Type指定的字符集来解析响应体。默认是UTF-8。

private final OkHttpClient client = new OkHttpClient();
    
    private final Gson gson = new Gson();
    
    
    
    public void run() throws Exception {
    
        Request request = new Request.Builder()
    
            .url("https://api.github.com/gists/c2a7c39532239ff261be")
    
            .build();
    
        Response response = client.newCall(request).execute();
    
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    
    
    
        Gist gist = gson.fromJson(response.body().charStream(), Gist.class);
    
        for (Map.Entry<String, GistFile> entry : gist.files.entrySet()) {
    
          System.out.println(entry.getKey());
    
          System.out.println(entry.getValue().content);
    
        }
    
    }
    
    
    
    static class Gist {
    
        Map<String, GistFile> files;
    
    }
    
    
    
    static class GistFile {
    
        String content;
    
    }

**响应缓存**  
为了缓存响应，你需要一个你可以读写的缓存目录，和缓存大小的限制。这个缓存目录应该是私有的，不信任的程序应不能读取缓存内容。  
一个缓存目录同时拥有多个缓存访问是错误的。大多数程序只需要调用一次new OkHttp()，在第一次调用时配置好缓存，然后其他地方只需要调用这个实例就可以了。否则两个缓存示例互相干扰，破坏响应缓存，而且有可能会导致程序崩溃。  
响应缓存使用HTTP头作为配置。你可以在请求头中添加Cache-Control: max-stale=3600 ,OkHttp缓存会支持。你的服务通过响应头确定响应缓存多长时间，例如使用Cache-Control: max-age=9600。

private final OkHttpClient client;
    
    
    
    public CacheResponse(File cacheDirectory) throws Exception {
    
        int cacheSize = 10 * 1024 * 1024; // 10 MiB
    
        Cache cache = new Cache(cacheDirectory, cacheSize);
    
    
    
        client = new OkHttpClient();
    
        client.setCache(cache);
    
    }
    
    
    
    public void run() throws Exception {
    
        Request request = new Request.Builder()
    
            .url("http://publicobject.com/helloworld.txt")
    
            .build();
    
    
    
        Response response1 = client.newCall(request).execute();
    
        if (!response1.isSuccessful()) throw new IOException("Unexpected code " + response1);
    
    
    
        String response1Body = response1.body().string();
    
        System.out.println("Response 1 response: " + response1);
    
        System.out.println("Response 1 cache response: " + response1.cacheResponse());
    
        System.out.println("Response 1 network response: " + response1.networkResponse());
    
    
    
        Response response2 = client.newCall(request).execute();
    
        if (!response2.isSuccessful()) throw new IOException("Unexpected code " + response2);
    
    
    
        String response2Body = response2.body().string();
    
        System.out.println("Response 2 response: " + response2);
    
        System.out.println("Response 2 cache response: " + response2.cacheResponse());
    
        System.out.println("Response 2 network response: " + response2.networkResponse());
    
    
    
        System.out.println("Response 2 equals Response 1? " + response1Body.equals(response2Body));
    
    }

转自 OkHttp使用介绍 同时整合了 OkHttp使用进阶 这篇文章以及其中的评论。

[http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2015/0106/2275.html][http_www.jcodecraeer.com_a_anzhuokaifa_androidkaifa_2015_0106_2275.html]

[http_www.jcodecraeer.com_a_anzhuokaifa_androidkaifa_2015_0106_2275.html]: http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2015/0106/2275.html