So if there is a java.io.StringBufferInputStream, you would think that there would be a StringBufferOutputStream.
Any ideas as to why there isn't??
Likewise,there is also a SequenceInputStream but no SequenceOutputStream.
My guess is that someone never got around to making a StringBufferOutputStream in Java 1.0 since the product was somewhat "rushed to market." By the time Java 1.1 rolled around and people actually understood that readers and writers were for characters, and inputstreams and outputstreams were for bytes, the whole concept of using streams for strings was realized to be wrong, so the StringBufferInputStream was rightly deprecated, with no chance ever of a partner coming along.
A SequenceInputStream is a nice way to read from a bunch of streams all concatenated together, but it doesn't make much sense to write a single stream to multiple streams. Well, I suppose you could make sense of this if you wanted to write a large stream into multiple partitions (reminds me of Hadoop here). It's just not common enough to be in a standard library. A complication here would be that you would need to specify the size of each output partition and would really only make sense for files (which can have names with increasing suffixes, perhaps), and so would not generalize into arbitrary output streams in a nice manner.
StringBufferInputStream is deprecated, because bytes and characters are not the same thing. The correct classes to use for this are StringReader and StringWriter.
If you think about it, there is no way to make a SequenceOutputStream work. SequenceInputStream reads from the first stream until it is exhausted, then reads from the next stream. Since an OutputStream is never exhausted (unless, say, it happens to be connected to a socket whose peer closes the connection), how would a SequenceOutputStream class know when to move on to the next stream?
StringBufferInputStream has long been depreciated.
Use StringReader and StringWriter.
Related
I'm looking for a good explaination of the difference between the "new" Streams in Java 8 and the "old" I/O Streams we had before in Java 7. For someone without any knowledge of functional programming, it's hard to get that those are complete different things, especially because the names are the same. I get that the Stream API is something completely new and even revolutionary in some point, but in my naive thinking, in both cases we deal with sequences of "things", be it bytes, data or objects...
Can someone please offer a good explaination?
It has nothing to do with each other and I agree, it's bad luck that IO Streams had their name before the "new" Streams have arrived. The I/O streams were meant as connections to external resources, mostly files, but also others. The new Streams are for functional programming and should be treated separately.
But you can actually use both concepts together. For example, a BufferedReader has a lines-method, which returns lines of a file (or other resources) as a Stream of Strings.
Let's take a look at the picture illustrated I/O stream.
There are three concerning concepts related to I/O stream: Source, Destination, and Element (represented by the letter 'e'), where
Source or Destination could by a file, network connection, pipe, memory buffer etc.
An Element is just simply a piece of data and a stream consist of a chunk of elements
When to use what?
I/O streams are for reading content from a source, or writing the content to a destination. That's it, simple :-)
The new Stream concept introduced in Java 8 has nothing to do with I/O streams. Streams are not themselves data structures, but Classes that allow you to manipulate a collection of data in a declarative way (functional-style operation).
In term of 'stream' there is no difference. Stream is abstract phrase that means something that has a source and destination. What is more it is something that represents sequence of data.
In term of these two mechanism there is a lot of differences. For example Java i/o streams let you only read and write data. If you want to process data from that stream there is no builded in mechanism for that. In Java 8 stream there are additional possibilities of processig like map/filter etc.
I am getting a hard time visualizing what exactly stream means in terms of IO. I imagine stream as a continuous flow of data coming from a file, socket or any other data source. Is that correct? But then I get confused on how our java programs react to stream because when we write any java code let say:
Customer getCustomer(Customer customer)
Doesn't the above java code expects the whole object to be present before it gets processed?
Now lets say we are reading from a stream something like
FileInputStream in = new FileInputStream("abc.txt")
in.read();
Doesn't in.read() expects the whole file to be present in memory to be processed. If it is, then how come it is a stream? Why do we call them streams? Do they process data as it is read?
A similar confusion when reading through hadoop streams, looks like they have a different meaning altogether.
The word "stream" is used for different things in different contexts. But you're specifically asking about streams in I/O, i.e. InputStream and OutputStream.
I imagine stream as a continuous flow of data coming from a file, socket or any other data source. Is that correct?
Yes, a stream is a source of a sequence of bytes, which may come from a file, socket etc.
About getCustomer: You need to have a Customer object to pass to that method. But calling methods, passing objects and getting objects returned really does not have anything to do with streams.
Doesn't in.read() expects the whole file to be present in memory to be processed.
No. FileInputStream is an object which represents the stream. It's the thing that knows how to read bytes from the file.
Streams are not a fundamentally special kind of object. It's not like that there are classes, objects and streams. Streams are just a concept that is implemented using the standard Java OO programming features (classes and objects).
Doesn't the above java code expects the whole object to be present before it gets processed?
Yes. But it's not a stream.
Doesn't in.read() expects the whole file to be present in memory to be processed.
No.
If it is
It isn't.
then how come it is a stream?
It is.
Why do we call them streams? Do they process data as it is read?
Yes.
A similar confusion
There is no confusion here, except your own confusion when comparing method calls with I/O streams, which comparing apples versus oranges.
when reading through hadoop streams, looks like they have a different meaning altogether.
Very possibly.
An I/O Stream represents an input source or an output destination. A stream can represent many different kinds of sources and destinations, including disk files, devices, other programs, and memory arrays.
Streams support many different kinds of data, including simple bytes, primitive data types, localized characters, and objects. Some streams simply pass on data; others manipulate and transform the data in useful ways.
No matter how they work internally, all streams present the same simple model to programs that use them: A stream is a sequence of data.
In Java there are two kinds of streams (Byte & Character), they differ in the way how the data is transferred between source & destination.
Hope this answers your question. Please let me know if you need any further information.
From here..
A Stream is a free flowing sequence of elements. They do not hold any storage as that responsibility lies with collections such as arrays, lists and sets. Every stream starts with a source of data, sets up a pipeline, processes the elements through a pipeline and finishes with a terminal operation. They allow us to parallelize the load that comes with heavy operations without having to write any parallel code. A new package java.util.stream was introduced in Java 8 to deal with this feature.
Streams adhere to a common Pipes and Filters software pattern. A pipeline is created with data events flowing through, with various intermediate operations being applied on individual events as they move through the pipeline. The stream is said to be terminated when the pipeline is disrupted with a terminal operation. Please keep in mind that a stream is expected to be immutable — any attempts to modify the collection during the pipeline will raise a ConcurrentModifiedException exception.
I am doing a project in which there are so many files I have to handle. Problem came when I have to provide file in different manner like:
File will contain one string in each line
numbers of char in each line e.g. :
1st line : A B 4
2nd line : 6 C A 6 & U #
etc.
File will contain no. of Strings e.g.
1st line : Lion Panther jaguar etc.
I have read how to efficiently handle file but I am so confused when to use Buffered Streams and when Unbuffered. If I am using BufferedStream then BufferInputStream and BufferReader / BufferWriter which should be used.
Similarly I am confuse with I/O Stream, File I/O Stream, ByteArray I/O Stream. There are so many things. Can any one suggest me when to use which one and why? What could be efficient handling according to the different scenarios?
Well, there might not be a direct answer for this, but you don't have to worry if you feel confused. Discussions about Buffered and Unbufferred have been done many times before.
For example in this link: bufferred vs non-bufferred, gives a good hint (check the answer marked as correct). This comes because while using Bufferred streams, those streams are stored in a small area of memory called (suprisingly) buffer. Same happens to written data (they go into the buffer before being stored into the hard memory). This improves performance because lowers the overhead of I/O operations (which are OS dependent). Check the Java Doc: Bufferred Streams
So, to make it clear, use Bufferred streams when you need to improve the performance of your I/O operations. Use Unbufferred streams when you want to ensure that the output has been written before continuing (because an error might always occur while writing from/into the buffer, an example might be when you want to write a log, it might be opened all the time, so there is no need to access it, no need for a buffer ).
I am reading from an InputStream.
and writing what I read into an outputStream.
I also check a few things.
Like if I read an
& (ampersand)
I need to write
"& amp;"
My code works. But now I wonder if I have written the most efficient way (which I doubt).
I read byte by byte. (but this is because I need to do odd modifications)
Can somebody who's done this suggest the fastest way ?
Thanks
If you are using BufferedInputStream and BufferedOutputStream then it is hard to make it faster.
BTW if you are processing the input as characters as opposed to bytes, you should use readers/writers with BufferedReader and BufferedWriter.
The code should be reading/writing characters with Readers and Writers. For example, if its in the middle of a UTF-8 sequence, or it gets the second half of a UCS-2 character and it happens to read the equivalent byte value of an ampersand, then its going to damage the data that its attempting to copy. Code usually lives longer than you would expect it to, and somebody might try to pick it up later and use it in a situation where this could really matter.
As far as being faster or slower, using a BufferedReader will probably help the most. If you're writing to the file system, a BufferedWriter won't make much of a difference, because the operating system will buffer writes for you and it does a good job. If you're writing to a StringWriter, then buffering will make no difference (may even make it slower), but otherwise buffering your writes ought to help.
You could rewrite it to process arrays; and that might make it faster. You can still do that with arrays. You will have to write more complicated code to handle boundary conditions. That also needs to be a factor in the decision.
Measure, don't guess, and be wary of opinions from people who aren't informed of all the details. Ultimately, its up to you ot figure out if its fast enough for this situation. There is no single answer, because all situations are different.
I would prefer to use BufferedReader for reading input and BufferedWriter for output. Using Regular Expressions for matching your input can make your code short and also improve your time complexity.
I have a BufferedReader looping through a file. When I hit a specific case, I would like to continue looping using a different instance of the reader but starting at this point.
Any ideas for a recommended solution? Create a separate reader, use the mark function, etc.?
While waiting for your answer to my comment, I'm stuck with making assumptions.
If it's the linewise input you value, you may be as pleasantly surprised as I was to discover that RandomAccessFile now (since 1.4 or 1.5) supports the readLine method. Of course RandomAccessFile gives you fine-grained control over position.
If you want buffered IO, you may consider wrapping a reader around a CharacterBuffer or maybe a ByteBuffer wrapped around a file mapped using the nio API. This gives you the ability to treat a file as memory, with fine control of the read pointer. And because the data is all in memory, buffering is included free of charge.
Have you looked at BufferedReader's mark method? Used in conjunction with reset it might meet your needs.
If you keep track of how many characters you've read so far, you can create a new BufferedReader and use skip.
As Noel has pointed out, you would need to avoid using BufferedReader.readLine(), since readLine() will discard newlines and make your character count inaccurate. You probably shouldn't count on readLine() never getting called if anyone else will ever have to maintain your code.
If you do decide to use skip, you should write your own buffered Reader which will give you an offset counting the newlines.