Java I/O FAQ   

This page is the FAQ for the "I/O and Streams" forum. It's editable by everyone, so add your own content as you see fit.

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Other FAQ pages that deal with I/O

• AccessingFileFormats - How to read and write various file formats

• ByteArrayBuffer - a class to read and write primitives from a byte array

• ReadDoesntDoWhatYouThinkItDoes

• AvailableDoesntDoWhatYouThinkItDoes

• How do I EditAnExistingFile

• The FileUpload page has hints on how to upload files to a server via FTP, SMB and HTTP.

• I'm getting a TooManyOpenFiles exception

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Links to articles elsewhere that relate to I/O

• A good introduction to Unicode: The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!) by Joel Spolsky

• Character Conversions from Browser to Database

• Changes in Java 5.0 for handling Unicode characters above 65535: John O'Conner Tom White Surrogates

• Overview of the java.nio package - nonblocking I/O

• Don't println to a Socket - some good hints on how not to do socket communication

• How to read the Windows Registry

• USB: How to access USB devices - Access USB devices from Java applications - jUSB library - libusb4j library

• Character Conversions from Browser to Database: article

• How to implement SSH, SFTP and SCP in Java: Ganymed SSH-2 for Java - JSch

• Connect through a Proxy

• Using ICMP packets (for ping and traceroute) in Java: Jpcap library

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Where can I get an implementation of the javax.comm API for Windows?

Sun does not provide an implementation of javax.comm version 3 for Windows, but version 2 can be used in conjunction with RXTX; see the javax.comm download page for further information. Other options (which do not implement the javax.comm API) are

• RXTX (open source)
• icaste (commercial)
• JCommSerial (commercial)
• SerialPort (commercial)

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When I try to construct an HTTPS URL, I get a java.net.MalformedURLException: unknown protocol: https. What gives?

JDK versions prior to 1.4 do not have HTTPS/SSL built in - they need an additional package called JSSE. Installation instructions can be found here. Then the JVM needs to be told what to do with HTTPS URLs, which can be done programmatically like this:

System.setProperty("java.protocol.handler.pkgs", "com.sun.net.ssl.internal.www.protocol");
//System.setProperty("https.proxyHost", proxyHost);
//System.setProperty("https.proxyPort", proxyPort);

Alternatively, you can specify this as a property on the command line:

 -Djava.protocol.handler.pkgs=com.sun.net.ssl.internal.www.protocol

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How can I set the client timeout when making an URL connection?

Starting with Java 5, this functionality is available in the JavaDoc:java.net.URLConnection class and its subclasses (like HttpURLConnection) via the getConnectTimeout/setConnectTimeout methods. For older Sun JVMs, a workaround is described here.

Jakarta Commons HttpClient also supports setting a timeout.

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How can I check the type of an image file?

The freely available ImageInfo class can identify certain image types: JPEG, PNG, GIF, BMP, PCX, IFF, RAS, PBM, PGM, PPM and PSD. It also determines certain image properties like height, width and color depth.

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How can I send SMS from a Java application?

You'll need an SMS library like smsj, SMSLib or smstools and a provider. You can find the latter by googling for "bulk sms http". This article may also be of interest.

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How can I use a modem from within Java? (or, to put it in another way, is there an implementation of JTAPI?)

The http://xtapi.sourceforge.net/ project "has providers for Microsoft’s TAPI, Serial Voice Modems, and Voice Over IP utilizing the OpenH323? Projects H.323 stack implementation".

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How can I determine the encoding of a given file?

That's what the jchardet and juniversalchardet libraries do.

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CategoryFaq