I want to intercept the standard output stream, then copy the content to another stream, but I also hope to keep the standard output stream like the original. Could I achieve that in Java?
You can use something like the example of TeeOutputStream explained here Writing Your Own Java I/O Stream Classes
Basically you create a TeeOutputStream, give it your stream and current System.out
then use System.setOut with the new stream.
Anything written to System.out will be written to the original System.out as well as your stream so you can do whatever you want with it
Edit:
Oracle took off this page, It is also possible to use TeeOutputStream from Apache Commons to do the same thing without adding any code.
Take a look at this package: org.apache.commons.io.output. I think that TeeOutputStream is what you're looking for.
Related
Looking at the documentation of Font#loadFont I came across this remark:
This method does not close the input stream.
Unfortunately, this is not explained or expanded upon. So my question is:
What are possible reasons the API won't close the input stream? Is it likely you would like to re-use the stream?
I mostly use this method like this:
Font.loadFont(getClass().getResourceAsStream("path/to/font"), 13.0);
to make sure the font is available for my application, so I never re-use the input stream, and I can't really think of a reason I'd want to.
Should I close the input stream myself? Should I expect any problems if I'm not closing the input stream?
In the past I've had problems with a font loaded this way, where some labels configured with this font started showing squares, while others (on the same scene!) kept working fine. Could this be related to not closing the input stream?
The documentation for every API involving scarce or external resources (such as file descriptors or streams) will make it clear whose responsibility it is to clean up (in this case, close the stream). This is sometimes referred to as "ownership".
In this case the documentation states that the loadFont method does not take ownership of the stream. Therefore it still belongs to you: It is your responsibility to close the stream.
The try-with-resources statement is the best way to do this.
Iam writing a map-reduce job in Java I would like to know is it possible to obtain output of the job as stream(may be a output stream) rather a physical output file. My objective is to use the stream for another application.
You can write a Custom Output Format and use that write to any stream you want to. Not necessarily a file. See this tutorial on how to write a Custom Output Format.
Or else you can make use Hadoop Streaming API. Have a look here for that.
I don't think you can do this using Apache-Hadoop. It is designed to work in a distributed system and AFAIK providing the way to emit an output stream would defy the purpose, as then how system would decide on the stream to emit, i.e. of which reducer! You may write to a flat-file/DB/amazon-s3 etc but perhaps you won't get a stream.
I searched and looked at multiple questions like this, but my question is really different than anything I found. I've looked at Java Docs.
How do I get the equivalent of this c file open:
stream1 = fopen (out_file, "r+b");
Once I've done a partial read from the file, the first write makes the next read return EOF no matter how many bytes were in the file.
Essentially I want a file I/O stream that doesn't do that. The whole purpose of what I'm trying to do is to replace the bytes in an existing file in the current file. I don't want to do it in a copy or make a copy before I do the Read->Write.
You can use a RandomAccessFile.
As Perception mentions, you can use a RandomAccessFile. Also, in some situations, a FileChannel may work better. I've used these to handle binary file data with great success.
EDIT: you can get a FileChannel from the RandomAccessFile object using getChannel.
Please suggest a method to obtain a similar behaviour in Java as when we do freopen("filename","r",stdin) OR freopen("filename","w",stdout) in C.
Assuming that this is to redirect stdin/stdout/stderr, have a look at System.setIn and friends. They allow you to assign a different InputStream and PrintStream to System.in, System.out and System.err.
See the webpage below. There's a solution to what you wanna do.
http://techtipshoge.blogspot.com/2011/01/connect-standard-io-to-files.html
I have a java applet for uploading files to server.
I want to display the % of data sent but when I use ObjectOutputStream.write() it just writes to the buffer, does not wait until the data has actually been sent. How can I achieve this.
Perhaps I need to use thread synchronization or something. Any clues would be most helpful.
Don't use ObjectOutputStream. It's for writing serialized Java objects, not for writing raw binary data. It may indeed block the stream. Rather just write directly to the OutputStream of the URL connection.
That said, the code looks pretty overcomplicated. Even after re-reading several times and blinking my eyes countless times, I can't get it right. I suggest you to send those files according the multipart/form-data encoding with help of Commons HttpClient. You can find here a basic code example. You just have to modify Part[] parts to include all the files. The servlet on the other side can in turn use Commons FileUpload to parse the multipart/form-data request.
To calculate the progress, I'd suggest to pick CountingOutputStream of Commons IO. Just wrap the OutputStream with it and write to it.
Update: if you don't like to ship your applet with more 3rd party libraries (which I imagine is reasonable), then have a look at this code snippet (and the original question mentioned as 1st link) how to create a multipart/form-data body yourself using URLConnection.
What I was looking for was actually:
setFixedLengthStreamingMode(int contentLength)
This prevents any internal buffering allowing me know exactly the amount of data being sent.