saker.build Documentation TaskDoc JavaDoc Packages
public final class HashContentDescriptor implements ContentDescriptor, Externalizable
ContentDescriptor implementation that is backed by a hash result.

When changes are being detected, this class compares the hash bytes to the arugment hash bytes.

When possible, the actual hash bytes of the underlying instance will also contain the number of bytes that were used to compute the hash.

A new instance can be created by calling one of the static factory methods.

Nested types
public static class
OutputStream which forwards any bytes written to it to an underlying MessageDigest.
Constructors
public
Methods
public static ContentDescriptor
Creates a new instance by initializing it with the specified hash.
public static ContentDescriptor
Creates a new instance by initializing it with the specified hash.
public static ContentDescriptor
createWithHash(byte[] hash)
Creates a new instance by initializing it with the specified hash.
public boolean
Indicates whether some other object is "equal to" this one.
public String
Gets a hexadecimal representation of the underlying hash bytes.
public static ContentDescriptor
Creates a new instance by hashing the bytes from the given input stream.
public static ContentDescriptor
Creates a new instance by hashing the bytes from the given input stream, using the given hasher.
public static ContentDescriptor
Creates a new instance by hashing the bytes from the given stream writable.
public static ContentDescriptor
Creates a new instance by hashing the bytes from the given stream writable, using the given hasher.
public static ContentDescriptor
Creates a new instance by hashing the argument byte data.
public static ContentDescriptor
Creates a new instance by hashing the argument byte data, using the given hasher.
public static ContentDescriptor
hash(byte[] data)
Creates a new instance by hashing the argument byte data.
public static ContentDescriptor
hash(byte[] data, int offset, int len)
Creates a new instance by hashing the argument byte data of the specified region.
public static ContentDescriptor
hash(byte[] data, int offset, int len, MessageDigest digest)
Creates a new instance by hashing the argument byte data of the specified region, using the given hasher.
public int
Returns a hash code value for the object.
public boolean
Detects changes between this content descriptor and the previous one.
public void
The object implements the readExternal method to restore its contents by calling the methods of DataInput for primitive types and readObject for objects, strings and arrays.
public String
Returns a string representation of the object.
public void
The object implements the writeExternal method to save its contents by calling the methods of DataOutput for its primitive values or calling the writeObject method of ObjectOutput for objects, strings, and arrays.
Inherited methods
From: Object
Creates a new instance by initializing it with the specified hash.
hashThe hash.
The created content descriptor.
NullPointerExceptionIf the argument is null.
Creates a new instance by initializing it with the specified hash.
hashThe hash.
The created content descriptor.
NullPointerExceptionIf the argument is null.
public static ContentDescriptor createWithHash(byte[] hash) throws NullPointerException
Creates a new instance by initializing it with the specified hash.
hashThe hash.
The created content descriptor.
NullPointerExceptionIf the argument is null.
public boolean equals(Object obj)
Overridden from: Object
Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

  • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
  • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
  • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
  • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
  • For any non-null reference value x, x.equals(null) should return false.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

objthe reference object with which to compare.
true if this object is the same as the obj argument; false otherwise.
Gets a hexadecimal representation of the underlying hash bytes.
The hash bytes in hexadecimal format.
Creates a new instance by hashing the bytes from the given input stream.
dataThe input stream of bytes.
The created content descriptor.
IOExceptionIn case of I/O error.
NullPointerExceptionIf argument is null.
Creates a new instance by hashing the bytes from the given input stream, using the given hasher.
dataThe input stream of bytes.
digestThe hasher.
The created content descriptor.
IOExceptionIn case of I/O error.
NullPointerExceptionIf any of the arguments are null.
Creates a new instance by hashing the bytes from the given stream writable.
dataThe stream writable of bytes.
The created content descriptor.
IOExceptionIn case of I/O error.
NullPointerExceptionIf argument is null.
Creates a new instance by hashing the bytes from the given stream writable, using the given hasher.
dataThe stream writable of bytes.
digestThe hasher.
The created content descriptor.
IOExceptionIn case of I/O error.
NullPointerExceptionIf any of the arguments are null.
Creates a new instance by hashing the argument byte data.
dataThe byte data.
The created content descriptor.
NullPointerExceptionIf the argument is null.
Creates a new instance by hashing the argument byte data, using the given hasher.
dataThe byte data.
digestThe hasher.
The created content descriptor.
NullPointerExceptionIf any of the arguments are null.
public static ContentDescriptor hash(byte[] data) throws NullPointerException
Creates a new instance by hashing the argument byte data.
dataThe byte data.
The created content descriptor.
NullPointerExceptionIf the argument is null.
public static ContentDescriptor hash(byte[] data, int offset, int len) throws NullPointerException
Creates a new instance by hashing the argument byte data of the specified region.
dataThe byte data.
offsetThe starting index in the array.
lenThe number of bytes to hash starting from the offset.
The created content descriptor.
NullPointerExceptionIf the array argument is null.
public static ContentDescriptor hash(byte[] data, int offset, int len, MessageDigest digest) throws NullPointerException
Creates a new instance by hashing the argument byte data of the specified region, using the given hasher.
dataThe byte data.
offsetThe starting index in the array.
lenThe number of bytes to hash starting from the offset.
digestThe hasher.
The created content descriptor.
NullPointerExceptionIf the array or hasher arguments are null.
public int hashCode()
Overridden from: Object
Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

The general contract of hashCode is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the Object.equals(Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the Java™ programming language.)

a hash code value for this object.
public boolean isChanged(ContentDescriptor o)
Overridden from: ContentDescriptor
Detects changes between this content descriptor and the previous one.

The default implementation compares the two objects using ContentDescriptor.equals(Object).

Implementations are encouraged to check the type of the parameter using instanceof before casting them. It is further encouraged to check the content differences against interfaces instead of direct class implementations.

One can think about this function as this is the expected content of a file, and the parameter is the actual contents. If this method returns true then the file associated with this should replace the file associated with the parameter contents. This is mainly used when synchronizing files in memory to the filesystem.

oThe previous content to examine. Might be null to represent that the previous content doesn't exist.
true if the contents described by this descriptor differs from the parameter.
Overridden from: Externalizable
The object implements the readExternal method to restore its contents by calling the methods of DataInput for primitive types and readObject for objects, strings and arrays. The readExternal method must read the values in the same sequence and with the same types as were written by writeExternal.
inthe stream to read data from in order to restore the object
IOExceptionif I/O errors occur
ClassNotFoundExceptionIf the class for an object being restored cannot be found.
public String toString()
Overridden from: Object
Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 
a string representation of the object.
public void writeExternal(ObjectOutput out) throws IOException
Overridden from: Externalizable
The object implements the writeExternal method to save its contents by calling the methods of DataOutput for its primitive values or calling the writeObject method of ObjectOutput for objects, strings, and arrays.
outthe stream to write the object to
IOExceptionIncludes any I/O exceptions that may occur