Matlab using Java openStream(url) get :Java exception occurred: java.lang.NullPointerException

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buer 2014-11-20

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https://ww2.mathworks.cn/matlabcentral/answers/163507-matlab-using-java-openstream-url-get-java-exception-occurred-java-lang-nullpointerexception

回答： buer 2014-12-17

Hi,

I want to download one file from a URL. According to this: http://www.mathworks.com/matlabcentral/newsreader/view_thread/294528. all works fine until i go to the line: is = jurl.openStream; This gave one error says Java exception occurred: java.lang.NullPointerException.

Anyone can help? thanks

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buer 2014-12-2

Hi Groff.

Thanks a lot. It is valid link..I got it solved by learning this http://stackoverflow.com/questions/1317931/how-do-i-provide-a-username-password-to-access-a-web-resource-using-matlab-urlre

This is the answer...thanks a lot.

Geoff Hayes 2014-12-2

Buer - good that you figured it out. Could you summarize it as an answer below?

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buer 2014-12-17

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https://ww2.mathworks.cn/matlabcentral/answers/163507-matlab-using-java-openstream-url-get-java-exception-occurred-java-lang-nullpointerexception#answer_162621

在 MATLAB Online 中打开

Yes. so the answer is Matlab urlread does not support authentication with lower level request. So we need to code firectly against the Java URL class to use them:

% Matlab's urlread() doesn't do HTTP Request params, so work directly with Java
jUrl = java.net.URL(url);
conn = jUrl.openConnection();
conn.setRequestProperty('Authorization', ['Basic ' base64encode([user ':' password])]);
conn.connect();
info.status = conn.getResponseCode();
info.errMsg = char(readstream(conn.getErrorStream()));
s = readstream(conn.getInputStream());
function out = base64encode(str)
% Uses Sun-specific class, but we know that is the JVM Matlab ships with
encoder = sun.misc.BASE64Encoder();
out = char(encoder.encode(java.lang.String(str).getBytes()));
function out = readstream(inStream)
%READSTREAM Read all bytes from stream to uint8
try
    import com.mathworks.mlwidgets.io.InterruptibleStreamCopier;
    byteStream = java.io.ByteArrayOutputStream();
    isc = InterruptibleStreamCopier.getInterruptibleStreamCopier();
    isc.copyStream(inStream, byteStream);
    inStream.close();
    byteStream.close();
    out = typecast(byteStream.toByteArray', 'uint8'); %'
catch err
    out = []; %HACK: quash
end