uk.org.ogsadai.activity.indexedfiles
Class FileReadingActivity

java.lang.Object
  |
  +--uk.org.ogsadai.activity.Activity
        |
        +--uk.org.ogsadai.activity.files.AbstractFileActivity
              |
              +--uk.org.ogsadai.activity.indexedfiles.FileReadingActivity

public class FileReadingActivity

extends AbstractFileActivity

An activity to read data from one or more binary or text files stored on the server. The file data is then written to an output which can be connected to another activity or delivered back to the user in the response document. See the activity user documentation for more details: OGSADAI/doc/interaction/activities/indexedfiles/readFile.html

Author:

The OGSA-DAI Project Team

COPYRIGHT_NOTICE

private static final java.lang.String COPYRIGHT_NOTICE

Copyright statement

See Also:

Constant Field Values

LOG

private static final DAILogger LOG

Logger object for logging in this class

BLOCK_SIZE

private static final int BLOCK_SIZE

Size of blocks when retrieving bytes from random access file (1024)

See Also:

Constant Field Values

mFilename

private java.lang.String mFilename

Name of the text or random access file

mFile

private java.io.File mFile

Text / random access file

mBinaryFile

private java.io.RandomAccessFile mBinaryFile

Random access file

mTextFile

private java.io.BufferedReader mTextFile

Text file reader

mBase64encode

private boolean mBase64encode

Is the output base64 encoded?

mIsBinaryFile

private boolean mIsBinaryFile

Do we have a binary/random access or a text file?

mOffset

private long mOffset

Offset - skipped bytes or lines

mLength

private long mLength

Number of bytes or lines to be read, -1 if reading to the end of the file

mOutput

private BlockWriter mOutput

Activity output - bytes/lines read

mInput

private BlockReader mInput

Activity input - names of files to read

FileReadingActivity

public FileReadingActivity(org.w3c.dom.Element element)
                    throws ActivityCreationException,
                           ActivitySpecificationException

initialise

public void initialise()
                throws ActivitySpecificationException,
                       ActivityExecutionException

Description copied from class: AbstractFileActivity

Gets the data resource accessor for the files data resource according to whether the users credentials permit this access.

Overrides:

initialise in class AbstractFileActivity

Throws:

ActivitySpecificationException - If the user is not permitted to access the resource.

ActivityExecutionException - If some internal problem occurs.

See Also:

Activity.initialise()

processFirst

protected void processFirst()

Description copied from class: Activity

This method is called during the first iteration of processing an activity. It can be overridden by subclasses to define some processing that should be done only once during the first iteration of the activity processing, for example evaluating a database query.

Overrides:

processFirst in class Activity

processBlock

protected void processBlock()

Description copied from class: Activity

Performs an iteration of the processing of an activity. This may involve reading a block of input data and writing a block of output data, or may involve some other kind of processing. When an activity is processed by the OGSA-DAI engine, this method will be invoked repeatedly until the activity either completes or stops due to an error or termination call. An implementation of this method should invoke the setCompleted method to indicate that processing is complete, or the setError method if an error occurs that will prevent the processing from completing.

Specified by:

processBlock in class Activity

cleanUp

protected void cleanUp()

Description copied from class: Activity

This method can be overridden by any Activity implementations that need to free up resources in the event of an error or intermediate termination of the activity processing.

Overrides:

cleanUp in class Activity

readFromTextFile

private boolean readFromTextFile()
                          throws DAIFileReadIOException

Reads one line from a text file mLength is the remaining number of lines to read

Throws:

DAIFileReadIOException - If there is a problem.

readFromBinaryFile

private int readFromBinaryFile()
                        throws DAIFileReadIOException

Reads a block of bytes from a file (at most mLength bytes), and puts it into the output stream

Throws:

DAIFileReadIOException - If there is a problem.

hasNextFile

private boolean hasNextFile()
                     throws ActivitySpecificationException,
                            ActivityExecutionException

Checks if there is another instruction waiting in the input stream and retrieves filename, offset and length.

The instruction is expected to be of form:

   <readFile>
     <file>FILE</file>
     <bytes offset="M" length="M"/>
   </readFile>
 

or

   <readFile>
     <file>FILE</file>
     <lines offset="M" length="M"/>
   </readFile>
 

Returns:

true if there is another instruction to process, false if there are no more instructions or the input stream is null.

Throws:

ActivitySpecificationException - If the instruction format is not as expected, the file name is missing, the offset and length are not numbers or are < 0.

ActivityExecutionException - If an internal parsing-related problem occurs.

parseOffsetAndLength

private void parseOffsetAndLength(java.lang.String namespace,
                                  org.w3c.dom.Element element)
                           throws ActivitySpecificationException

Extracts offset and length attributes from an element that contains either a bytes or lines subelement and stores these.

Parameters:

namespace - Namespace of elements in element.

element - Element to parse.

Throws:

ActivitySpecificationException - If the offset and length are not numbers or are < 0.

openFile

private boolean openFile(java.lang.String filename)
                  throws ActivitySpecificationException,
                         ActivityExecutionException

Opens a file and skips mOffset lines or bytes

Parameters:

filename - Name of file to open.

Returns:

true if the file has been openend and the cursor is positioned after the offset, false if the file is not open (e.g. because the offset is larger than the length of the file

Throws:

ActivitySpecificationException - If the file does not exist or is outside the root directory

ActivityExecutionException - If some internal problem arises.