Home > Articles > Programming > Java

  • Print
  • + Share This
This chapter is from the book

20.2 Byte Streams

The java.io package defines abstract classes for basic byte input and output streams. These abstract classes are then extended to provide several useful stream types. Stream types are almost always paired: For example, where there is a FileInputStream to read from a file, there is usually a FileOutputStream to write to a file.

Before you can learn about specific kinds of input and output byte streams, it is important to understand the basic InputStream and OutputStream abstract classes. The type tree for the byte streams of java.io in Figure 20-1 shows the type hierarchy of the byte streams.

20fig01.jpg

Figure 20-1 Type Tree for Byte Streams in java.io

All byte streams have some things in common. For example, all streams support the notion of being open or closed. You open a stream when you create it, and can read or write while it is open. You close a stream with its close method, defined in the Closeable [1] interface. Closing a stream releases resources (such as file descriptors) that the stream may have used and that should be reclaimed as soon as they are no longer needed. If a stream is not explicitly closed it will hold on to these resources. A stream class could define a finalize method to release these resources during garbage collection but, as you learned on page 449, that could be too late. You should usually close streams when you are done with them.

All byte streams also share common synchronization policies and concurrent behavior. These are discussed in Section 20.5.1 on page 515.

20.2.1 InputStream

The abstract class InputStream declares methods to read bytes from a particular source. InputStream is the superclass of most byte input streams in java.io, and has the following methods:

  • public abstract int read() throws IOException
    • Reads a single byte of data and returns the byte that was read, as an integer in the range 0 to 255, not –128 to 127; in other words, the byte value is treated as unsigned. If no byte is available because the end of the stream has been reached, the value –1 is returned. This method blocks until input is available, the end of stream is found, or an exception is thrown. The read method returns an int instead of an actual byte value because it needs to return all valid byte values plus a flag value to indicate the end of stream. This requires more values than can fit in a byte and so the larger int is used.
  • public int read(byte[] buf, int offset, int count) throws IOException
    • Reads into a part of a byte array. The maximum number of bytes read is count. The bytes are stored from buf[offset] up to a maximum of buf[offset+count-1]—all other values in buf are left unchanged. The number of bytes actually read is returned. If no bytes are read because the end of the stream was found, the value –1 is returned. If count is zero then no bytes are read and zero is returned. This method blocks until input is available, the end of stream is found, or an exception is thrown. If the first byte cannot be read for any reason other than reaching the end of the stream—in particular, if the stream has already been closed—an IOException is thrown. Once a byte has been read, any failure that occurs while trying to read subsequent bytes is not reported with an exception but is treated as encountering the end of the stream—the method completes normally and returns the number of bytes read before the failure occurred.
  • public int read(byte[] buf) throws IOException
    • Equivalent to read(buf,0, buf.length).
  • public long skip(long count) throws IOException
    • Skips as many as count bytes of input or until the end of the stream is found. Returns the actual number of bytes skipped. If count is negative, no bytes are skipped.
  • public int available() throws IOException
    • Returns the number of bytes that can be read (or skipped over) without blocking. The default implementation returns zero.
  • public void close() throws IOException
    • Closes the input stream. This method should be invoked to release any resources (such as file descriptors) associated with the stream. Once a stream has been closed, further operations on the stream will throw an IOException. Closing a previously closed stream has no effect. The default implementation of close does nothing.

The implementation of InputStream requires only that a subclass provide the single-byte variant of read because the other read methods are defined in terms of this one. Most streams, however, can improve performance by overriding other methods as well. The default implementations of available and close will usually need to be overridden as appropriate for a particular stream.

The following program demonstrates the use of input streams to count the total number of bytes in a file, or from System.in if no file is specified:

import java.io.*;

class CountBytes {
    public static void main(String[] args)
        throws IOException
    {
        InputStream in;
        if (args.length == 0)
            in = System.in;
        else
            in = new FileInputStream(args[0]);

        int total = 0;
        while (in.read() != -1)
            total++;

        System.out.println(total + " bytes");
    }
}

This program takes a filename from the command line. The variable in represents the input stream. If a file name is not provided, it uses the standard input stream System.in; if one is provided, it creates an object of type FileInputStream, which is a subclass of InputStream.

The while loop counts the total number of bytes in the file. At the end, the results are printed. Here is the output of the program when used on itself:

318 bytes

You might be tempted to set total using available, but it won't work on many kinds of streams. The available method returns the number of bytes that can be read without blocking. For a file, the number of bytes available is usually its entire contents. If System.in is a stream associated with a keyboard, the answer can be as low as zero; when there is no pending input, the next read will block.

20.2.2 OutputStream

The abstract class OutputStream is analogous to InputStream; it provides an abstraction for writing bytes to a destination. Its methods are:

  • public abstract void write(int b) throws IOException
    • Writes b as a byte. The byte is passed as an int because it is often the result of an arithmetic operation on a byte. Expressions involving bytes are type int, so making the parameter an int means that the result can be passed without a cast to byte. Note, however, that only the lowest 8 bits of the integer are written. This method blocks until the byte is written.
  • public void write(byte[] buf, int offset, int count) throws IOException
    • Writes part of an array of bytes, starting at buf[offset] and writing count bytes. This method blocks until the bytes have been written.
  • public void write(byte[] buf) throws IOException
    • Equivalent to write(buf,0, buf.length).
  • public void flush() throws IOException
    • Flushes the stream. If the stream has buffered any bytes from the various write methods, flush writes them immediately to their destination. Then, if that destination is another stream, it is also flushed. One flush invocation will flush all the buffers in a chain of streams. If the stream is not buffered, flush may do nothing—the default implementation. This method is defined in the Flushable interface.
  • public void close() throws IOException
    • Closes the output stream. This method should be invoked to release any resources (such as file descriptors) associated with the stream. Once a stream has been closed, further operations on the stream will throw an IOException. Closing a previously closed stream has no effect.The default implementation of close does nothing.

The implementation of OutputStream requires only that a subclass provide the single-byte variant of write because the other write methods are defined in terms of this one. Most streams, however, can improve performance by overriding other methods as well. The default implementations of flush and close will usually need to be overridden as appropriate for a particular stream—in particular, buffered streams may need to flush when closed.

Here is a program that copies its input to its output, translating one particular byte value to a different one along the way. The TranslateByte program takes two parameters: a from byte and a to byte. Bytes that match the value in the string from are translated into the value in the string to.

import java.io.*;

class TranslateByte {
    public static void main(String[] args)
        throws IOException
    {
        byte from = (byte) args[0].charAt(0);
        byte to   = (byte) args[1].charAt(0);
        int b;
        while ((b = System.in.read()) != -1)
            System.out.write(b == from ? to : b);
    }
}

For example, if we invoked the program as

java TranslateByte b B

and entered the text abracadabra!, we would get the output

aBracadaBra!

Manipulating data from a stream after it has been read, or before it is written, is often achieved by writing Filter streams, rather than hardcoding the manipulation in a program. You'll learn about filters in Section 20.5.2 on page 516.

Exercise 20.1 : Rewrite the TranslateByte program as a method that translates the contents of an InputStream onto an OutputStream, in which the mapping and the streams are parameters. For each type of InputStream and OutputStream you read about in this chapter, write a new main method that uses the translation method to operate on a stream of that type. If you have paired input and output streams, you can cover both in one main method.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020