Question

我为检查网址编写了这个方法。

public boolean checkresume(String URL) throws IOException{
    HttpURLConnection urlc;
    urlc = (HttpURLConnection)new URL(url).openConnection();
    urlc.setRequestProperty("Range", "bytes="+1+"-");
    urlc.getResponseCode();
    Log.e("Check Resume",urlc.getHeaderField("Accept-Ranges").toString());
    if((urlc.getHeaderField("Accept-Ranges").equals("bytes"))){
        return true;
    }else{
        return false;
    }
}

导入具有继续URL功能的URL时，此方法没有错误，返回＆＃34; true＆＃34;。

但是，当导入无法继续URL的URL时，崩溃的应用程序并返回此日志

网址示例：https://codeload.github.com/libuchao/Dictionary/zip/master

日志：

08-01 13:25:12.201: E/AndroidRuntime(8466): FATAL EXCEPTION: main
08-01 13:25:12.201: E/AndroidRuntime(8466): Process: com.yyxu.download, PID: 8466
08-01 13:25:12.201: E/AndroidRuntime(8466): java.lang.RuntimeException: Unable to start service com.yyxu.download.services.DownloadService@429f1b38 with Intent { act=com.yyxu.download.services.IDownloadService (has extras) }: java.lang.NullPointerException
08-01 13:25:12.201: E/AndroidRuntime(8466):     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2877)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at android.app.ActivityThread.access$2200(ActivityThread.java:161)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1362)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at android.os.Handler.dispatchMessage(Handler.java:102)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at android.os.Looper.loop(Looper.java:157)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at android.app.ActivityThread.main(ActivityThread.java:5356)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at java.lang.reflect.Method.invokeNative(Native Method)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at java.lang.reflect.Method.invoke(Method.java:515)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at dalvik.system.NativeStart.main(Native Method)
08-01 13:25:12.201: E/AndroidRuntime(8466): Caused by: java.lang.NullPointerException
08-01 13:25:12.201: E/AndroidRuntime(8466):     at com.yyxu.download.services.DownloadTask.checkresume(DownloadTask.java:92)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at com.yyxu.download.services.DownloadTask.<init>(DownloadTask.java:76)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at com.yyxu.download.services.DownloadManager.newDownloadTask(DownloadManager.java:517)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at com.yyxu.download.services.DownloadManager.newDownloadTask(DownloadManager.java:342)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at com.yyxu.download.services.DownloadManager.addTask(DownloadManager.java:86)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at com.yyxu.download.services.DownloadService.onStart(DownloadService.java:58)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at android.app.Service.onStartCommand(Service.java:450)
08-01 13:25:12.201: E/AndroidRuntime(8466):     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2860)
08-01 13:25:12.201: E/AndroidRuntime(8466):     ... 10 more

问题是com.yyxu.download.services.DownloadTask.checkresume(DownloadTask.java:92)

第92行是：Log.e("Check Resume",urlc.getHeaderField("Accept-Ranges").toString());

请帮帮我。

我很抱歉我说英语。

感谢。

Answer 1

getHeaderField(String name)返回named的值标头字段，如果标头中没有此类字段，则为null。此方法返回String，因此无需使用toString()。

这仅表示您的URLConnection没有名为Accept-Ranges的标题字段。确保您使用标题的确切名称，因为它区分大小写。您还可以使用HttpURLConnection方法从数字getHeaderField(int n)获取标头返回nth标头。但更重要的是，您应该在使用它之前进行null检查以避免NPE这样：

if(urlc.getHeaderField("Accept-Ranges") != null) {
    // ... Move ahead

java中的URL check resume方法

1 个答案: