java.security: public class: DigestInputStream

java.security
public class: DigestInputStream [javadoc | source]

java.lang.Object
   java.io.InputStream
      java.io.FilterInputStream
         java.security.DigestInputStream

All Implemented Interfaces:
Closeable

A transparent stream that updates the associated message digest using the bits going through the stream.

To complete the message digest computation, call one of the digest methods on the associated message digest after your calls to one of this digest input stream's read methods.

It is possible to turn this stream on or off (see on ). When it is on, a call to one of the read methods results in an update on the message digest. But when it is off, the message digest is not updated. The default is for the stream to be on.

Note that digest objects can compute only one digest (see MessageDigest ), so that in order to compute intermediate digests, a caller should retain a handle onto the digest object, and clone it for each digest to be computed, leaving the orginal digest untouched.

Also see:

MessageDigest

DigestOutputStream

author: Benjamin - Renaud

Field Summary
protected MessageDigest	digest	The message digest associated with this stream.

Fields inherited from java.io.FilterInputStream:
in

Constructor:

Constructor:
public DigestInputStream(InputStream stream, MessageDigest digest) { super(stream); setMessageDigest(digest); } Creates a digest input stream, using the specified input stream and message digest. Parameters: `stream` - the input stream. `digest` - the message digest to associate with this stream.

 public DigestInputStream(InputStream stream,
    MessageDigest digest) {
        super(stream);
        setMessageDigest(digest);
}

Creates a digest input stream, using the specified input stream and message digest.

Parameters:

stream - the input stream.

digest - the message digest to associate with this stream.

Method from java.security.DigestInputStream Summary:
getMessageDigest, on, read, read, setMessageDigest, toString

Methods from java.io.FilterInputStream:
available, close, mark, markSupported, read, read, read, reset, skip

Methods from java.io.InputStream:
available, close, mark, markSupported, read, read, read, reset, skip

Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from java.security.DigestInputStream Detail:
public MessageDigest getMessageDigest() { return digest; } Returns the message digest associated with this stream.
public void on(boolean on) { this.on = on; } Turns the digest function on or off. The default is on. When it is on, a call to one of the `read` methods results in an update on the message digest. But when it is off, the message digest is not updated.
public int read() throws IOException { int ch = in.read(); if (on && ch != -1) { digest.update((byte)ch); } return ch; } Reads a byte, and updates the message digest (if the digest function is on). That is, this method reads a byte from the input stream, blocking until the byte is actually read. If the digest function is on (see on ), this method will then call `update` on the message digest associated with this stream, passing it the byte read.
public int read(byte[] b, int off, int len) throws IOException { int result = in.read(b, off, len); if (on && result != -1) { digest.update(b, off, result); } return result; } Reads into a byte array, and updates the message digest (if the digest function is on). That is, this method reads up to `len` bytes from the input stream into the array `b`, starting at offset `off`. This method blocks until the data is actually read. If the digest function is on (see on ), this method will then call `update` on the message digest associated with this stream, passing it the data.
public void setMessageDigest(MessageDigest digest) { this.digest = digest; } Associates the specified message digest with this stream.
public String toString() { return "[Digest Input Stream] " + digest.toString(); } Prints a string representation of this digest input stream and its associated message digest object.

Method from java.security.DigestInputStream Detail:

 public MessageDigest getMessageDigest() {
        return digest;
}

Returns the message digest associated with this stream.

 public  void on(boolean on) {
        this.on = on;
}

read

 public int read() throws IOException {
        int ch = in.read();
        if (on && ch != -1) {
            digest.update((byte)ch);
        }
        return ch;
}

update

 public int read(byte[] b,
    int off,
    int len) throws IOException {
        int result = in.read(b, off, len);
        if (on && result != -1) {
            digest.update(b, off, result);
        }
        return result;
}

len

b

off

update

 public  void setMessageDigest(MessageDigest digest) {
        this.digest = digest;
}

Associates the specified message digest with this stream.

 public String toString() {
         return "[Digest Input Stream] " + digest.toString();
}

Prints a string representation of this digest input stream and its associated message digest object.