我们知道OkHttp走的并不是原生的http请求，因此在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？
一、获取User-Agent
private static String getUserAgent() { String userAgent = ""; if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) { try { userAgent = WebSettings.getDefaultUserAgent(context); } 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(); } 代码说明：
1. 在Android 17之后可以通过WebSettings.getDefaultUserAgent(context)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；
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
第二种：
Dalvik/2.1.0 (Linux; U; Android 6.0.1; MI 4LTE MIUI/6.10.13)
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
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/537.36at 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$MethodAndArgsCaller.run(ZygoteInit.java:828)at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644)at dalvik.system.NativeStart.main(Native Method)Caused by: java.lang.IllegalArgumentException: Unexpected char 0x7231 at 33 in User-Agent value: Mozilla/5.0 (Linux; Android 5.1; 爱国者-X86 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/30.0.0.0 Safari/537.36at okhttp3.Headers$Builder.checkNameAndValue(Headers.java:320)at okhttp3.Headers$Builder.add(Headers.java:270)at okhttp3.Request$Builder.addHeader(Request.java:175)
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，如果不符合条件就抛出异常IllegalArgumentException
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)); } } } 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。
二、给Okhttp设置User-Agent
Request request = new Request.Builder().url(url).removeHeader("User-Agent").addHeader("User-Agent", getUserAgent()).build();httpClient.newCall(request).enqueue(handler);