<p>我们知道Okhttp走的并不是原生的http请求，因此他在header里面并没有真正的User-Agent，而是“okhttp/版本号”这样的字符串，因为后台需要统计信息，要求传入正确的User-Agent，那么我们如何获取User-Agent并设置给Okhttp呢？</p>    <h2>0x01-正确获取useragent</h2>    <pre>  <code class="language-java">private static String getUserAgent() {          String userAgent = "";          if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {              try {                  userAgent = WebSettings.getDefaultUserAgent(AllyApp.getInstance());              } catch (Exception e) {                  userAgent = System.getProperty("http.agent");              }          } else {              userAgent = System.getProperty("http.agent");          }          StringBuffer sb = new StringBuffer();          for (int i = 0, length = userAgent.length(); i < length; i++) {              char c = userAgent.charAt(i);              if (c <= '\u001f' || c >= '\u007f') {                  sb.append(String.format("\\u%04x", (int) c));              } else {                  sb.append(c);              }          }          return sb.toString();      }</code></pre>    <p>代码说明：</p>    <p>1、在Api17之后可以通过 WebSettings.getDefaultUserAgent(AllyApp.getInstance()) 获取，但是经过测试极个别手机会出现找不到类的情况，因此try-catch一下，那么第二种方式是 System.getProperty("http.agent") ,这两种方式有什么不同呢？从结果上来看是第一种得到的信息更全一点；</p>    <p>第一种：</p>    <pre>  <code class="language-java">Mozilla/5.0 (Linux; Android 6.0.1; MI 4LTE Build/MMB29M; wv) AppleWebKit/537.36 (KHTML, like Gecko)   Version/4.0 Chrome/51.0.2704.81 Mobile Safari/537.36</code></pre>    <p>第二种：</p>    <pre>  <code class="language-java">Dalvik/2.1.0 (Linux; U; Android 6.0.1; MI 4LTE MIUI/6.10.13)</code></pre>    <p>2、在一些国产手机上面这个User-Agent里面会包含中文，就会报错</p>    <pre>  <code class="language-java">java.lang.IllegalArgumentException: Unexpected char 0x7231 at 33 in User-Agent value: Mozilla/5.0 (Linux; Android 5.1; 爱国者-X86 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/30.0.0.0 Safari/537.36  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2367)  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2419)  at android.app.ActivityThread.access$800(ActivityThread.java:151)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1342)  at android.os.Handler.dispatchMessage(Handler.java:110)  at android.os.Looper.loop(Looper.java:193)  at android.app.ActivityThread.main(ActivityThread.java:5323)  at java.lang.reflect.Method.invokeNative(Native Method)  at java.lang.reflect.Method.invoke(Method.java:515)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:828)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644)  at dalvik.system.NativeStart.main(Native Method)  Caused by: java.lang.IllegalArgumentException: Unexpected char 0x7231 at 33 in User-Agent value: Mozilla/5.0   (Linux; Android 5.1; 爱国者-X86 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/30.0.0.0 Safari/537.36  at okhttp3.Headers$Builder.checkNameAndValue(Headers.java:320)  at okhttp3.Headers$Builder.add(Headers.java:270)  at okhttp3.Request$Builder.addHeader(Request.java:175)</code></pre>    <p>什么原因引起的呢？ okhttp3.Headers$Builder.checkNameAndValue 进到这个方法里面可以看到okhttp对中文进行了过滤，如果不是中文就抛出异常 IllegalArgumentException</p>    <pre>  <code class="language-java">private void checkNameAndValue(String name, String value) {        if (name == null) throw new NullPointerException("name == null");        if (name.isEmpty()) throw new IllegalArgumentException("name is empty");        for (int i = 0, length = name.length(); i < length; i++) {          char c = name.charAt(i);          if (c <= '\u001f' || c >= '\u007f') {            throw new IllegalArgumentException(Util.format(                "Unexpected char %#04x at %d in header name: %s", (int) c, i, name));          }        }        if (value == null) throw new NullPointerException("value == null");        for (int i = 0, length = value.length(); i < length; i++) {          char c = value.charAt(i);          if (c <= '\u001f' || c >= '\u007f') {            throw new IllegalArgumentException(Util.format(                "Unexpected char %#04x at %d in %s value: %s", (int) c, i, name, value));          }        }      }</code></pre>    <p>因此上段代码才会对返回结果进行过滤，如果不符合条件，会进行转码。</p>    <h2>0x02-给Okhttp设置User-Agent</h2>    <pre>  <code class="language-java">Request request = new Request.Builder().url(url).removeHeader("User-Agent").addHeader("User-Agent",                  getUserAgent()).build();  httpClient.newCall(request).enqueue(handler);</code></pre>    <p> </p>    <p>来自：http://www.jianshu.com/p/ddbe8c637fc5</p>    <p> </p>