Chapter 18
The java.util.zip Package

CheckedInputStream

Name

CheckedInputStream

Synopsis

Class Name:

java.util.zip.CheckedInputStream

Superclass:

java.io.FilterInputStream

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

New as of JDK 1.1

The CheckedInputStream class represents an InputStream with an associated checksum. In other words, a CheckedInputStream wraps a regular input stream and computes a checksum value as data is read from the stream. The checksum can verify the integrity of the data. When you create a CheckedInputStream, you must specify an object that implements the Checksum interface that computes the checksum.

Class Summary

public class java.util.zip.CheckedInputStream 
             extends java.io.FilterInputStream {
  // Constructors
  public CheckedInputStream(InputStream in, Checksum cksum);
  
  // Instance Methods
  public Checksum getChecksum();
  public int read();
  public int read(byte[] buf, int off, int len);
  public long skip(long n);
}

Constructors

CheckedInputStream

public CheckedInputStream(InputStream in, Checksum cksum)

Parameters

in

The underlying input stream to use as a data source.

cksum

The checksum object.

Description

This constructor creates a CheckedInputStream that reads data from the given InputStream and updates the given Checksum.

Instance Methods

getChecksum

public Checksum getChecksum()

Returns

The Checksum associated with this input stream.

Description

This method returns the Checksum object associated with this input stream.

read

public int read() throws IOException

Returns

The next byte from the stream or -1 if the end of the stream has been reached.

Throws

IOException: If any kind of I/O error occurs.

Overrides

FilterInputStream.read()

Description

This method reads the next byte from the underlying InputStream and then updates the checksum. The method blocks until some data is available, the end of the stream is detected, or an exception is thrown.

public int read(byte[] buf, int off, int len) throws IOException

Parameters

buf

An array of bytes to be filled from the stream.

off

An offset into the byte array.

len

The number of bytes to read.

Returns

The number of bytes read or -1 if the end of the stream is encountered immediately.

Throws

IOException: If any kind of I/O error occurs.

Overrides

FilterInputStream.read(byte[], int, int)

Description

This method reads up to len bytes from the underlying InputStream and places them into the given array starting at off. The checksum is then updated with the data that has been read. The method blocks until some data is available.

skip

public long skip(long n) throws IOException

Parameters

n: The number of bytes to skip.

Returns

The actual number of bytes skipped.

Throws

IOException: If any kind of I/O error occurs.

Overrides

FilterInputStream.skip()

Description

This method skips over the specified number of bytes in the underlying InputStream. The skipped bytes are not calculated into the checksum.

Inherited Methods

Method	Inherited From	Method	Inherited From
`available()`	`FilterInputStream`	`clone()`	`Object`
`close()`	`FilterInputStream`	`equals(Object)`	`Object`
`finalize()`	`Object`	`getClass()`	`Object`
`hashCode()`	`Object`	`mark(int)`	`FilterInputStream`
`markSupported()`	`FilterInputStream`	`notify()`	`Object`
`notifyAll()`	`Object`	`read(byte[])`	`FilterInputStream`
`reset()`	`FilterInputStream`	`toString()`	`Object`
`wait()`	`Object`	`wait(long)`	`Object`
`wait(long, int)`	`Object`