我正在尝试使用 HttpURLConnection 从 url 中读取一些信息,但是,当我尝试运行它时,我得到:
java.lang.RuntimeException: Unable to start activity ComponentInfo{...}: java.lang.NullPointerException: println needs a message.
我见过很多这样做的例子,那么问题是什么?我已经仔细检查了 url,当我将它复制/粘贴到网络浏览器时,我收到了我应该收到的消息,没问题。我使用相同的 url 将信息获取到不同的程序(用 C++ 编写)并且在那里工作得很好。是否有我错过的连接设置或其他什么?
这是代码,问题出现在“InputStream stream = connection.getInputStream();”:
public String download_organisations(String url){
String jsonString = "";
try {
if(!url.startsWith("http://")){
url = "http://" + url;
}
if(url.endsWith("/")){
url = url.substring(0, url.lastIndexOf("/"));
}
url = url + SystemStatic.URL_SERVICE_WEB_ORGANISATION_MANAGER;
Log.d("OrganisationManager-Android","url: " + url);
URL httpUrl = new URL(url);
HttpURLConnection connection = (HttpURLConnection) httpUrl.openConnection();
connection.setConnectTimeout(10000);
InputStream stream = connection.getInputStream();
ByteArrayOutputStream buffer = new ByteArrayOutputStream();
int nRead;
byte[] data = new byte[1024];
while ((nRead = stream.read(data, 0, data.length)) != -1) {
buffer.write(data, 0, nRead);
}
buffer.flush();
byte[] inputStreamByteArray = buffer.toByteArray();
byte[] base64 = Base64.decode(inputStreamByteArray, 0);
byte[] decrypted = CipherUtils.decrypt(base64);
jsonString = decrypted.toString();
if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
Log.d("OrganisationManager-Android", "Download succeded with response: " + connection.getResponseCode());
} else {
Log.d("OrganisationManager-Android", "Download failed with response: " + connection.getResponseCode());
}
} catch (MalformedURLException e) {
Log.e("OrganisationManager-Android", e.getMessage());
} catch (IOException e) {
Log.e("OrganisationManager-Android", e.getMessage());
} catch (Exception e) {
Log.e("OrganisationManager-Android", e.getMessage());
}
return jsonString;
}
错误栈:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.organisationmanager.cin, PID: 2066
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.organisationmanager.cin/com.organisationmanager.ble.ScanningActivity}: java.lang.NullPointerException: println needs a message
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3194)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
Caused by: java.lang.NullPointerException: println needs a message
at android.util.Log.println_native(Native Method)
at android.util.Log.e(Log.java:261)
at com.organisationmanager.ble.common.OrganisationManagerWebPortalCommunicationHelper.download_organisations(OrganisationManagerWebPortalCommunicationHelper.java:210)
at com.organisationmanager.ble.ScanningActivity.onCreate(ScanningActivity.java:184)
at android.app.Activity.performCreate(Activity.java:7372)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1218)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3147)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
最佳答案
错误堆栈显示:
Caused by: java.lang.NullPointerException: println needs a message at android.util.Log.println_native(Native Method) at android.util.Log.e(Log.java:261)
从这些行可以看出,Log.e()
引发了异常在其中一个 catch
里面的方 block download_organisations()
(捕获 MalformedURLException
的那个,或者捕获 IOException
的那个,或者捕获 Exception
的那个)。
您在 catch
中处理异常通过记录他们的消息来阻止。但也许他们的信息是null
, 所以 println
没有要打印的有效消息并抛出 NullPointerException
.
尝试记录 e
相反,并检查是否再次抛出“java.lang.NullPointerException: println needs a message
”。这样做:
} catch (IOException e) {
Log.e("OrganisationManager-Android", e.toString());
}
否则你可以打印捕获异常的堆栈跟踪:
} catch (IOException e) {
Log.e("OrganisationManager-Android");
e.printStackTrace()
}
关于java - 尝试使用 HttpURLConnection 从 url 读取信息时出现 NullPointerException,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51825230/