Package com.storedobject.core

Class StreamContentProducer

java.lang.Object

com.storedobject.core.StreamContentProducer

All Implemented Interfaces:

Executable, ContentProducer, ContentType, RequiresTransactionManager, Closeable, AutoCloseable, Runnable

Direct Known Subclasses:

AbstractSpreadSheet, ImageProducer, TextContentProducer

public abstract class StreamContentProducer
extends Object
implements ContentProducer, Closeable

The StreamContentProducer class is an abstract implementation of the ContentProducer interface with additional support for managing output streams, transaction management, and access control. This class is designed for producing content in a stream-based manner, where the actual content generation must be implemented by subclasses.

It provides facilities for handling concurrent execution, stream and writer management, and integration with a transaction management system. Additionally, it incorporates mechanisms for determining and enforcing content access restrictions.

Author:

Syam

Field Summary

Fields

Modifier and Type	Field	Description
protected Entity	entity
protected OutputStream	out

Constructor Summary

Constructors

Constructor	Description
StreamContentProducer()	Default constructor for creating a StreamContentProducer instance.
StreamContentProducer(OutputStream out)	Constructs a StreamContentProducer with the specified output stream.

Method Summary

Modifier and Type	Method	Description
void	abort(Throwable error)	This method may be called when the content generation is aborted due to some error.
void	close()
abstract void	generateContent()	Generate the content here and write to 'out'
InputStream	getContent()	Retrieves the content as an InputStream.
final Entity	getEntity()	Retrieves the Entity associated with the current context.
Throwable	getError()	Get the current error (set via ContentProducer.abort(Throwable)).
String	getFileName()	Retrieves the name of the file associated with the content.
final ReportFormat	getReportFormat()	Retrieves the report format configuration associated with the current transaction manager or entity context.
TransactionManager	getTransactionManager()	Retrieves the transaction manager associated with this object.
protected Writer	getWriter()
static boolean	isBlocked(ContentProducer contentProducer, String type)
final boolean	isBlocked(String type)
void	produce()	Initiates the content production process and manages its lifecycle.
void	ready()	Waits for the readiness signal, blocking the current thread until the condition is met.
void	setTransactionManager(TransactionManager tm)	Sets the transaction manager for this object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface com.storedobject.core.ContentProducer

execute, extractContent, getFileExtension, getStreamData, getStreamDataProvider, getSystemEntity, saveTo, saveTo, saveTo, saveTo

Methods inherited from interface com.storedobject.core.ContentType

getContentType, getLink, getMimeType, isAudio, isHTML, isImage, isLink, isMedia, isPDF, isText, isVideo

Methods inherited from interface com.storedobject.common.Executable

act, run

Field Details

out

protected OutputStream out

entity

protected Entity entity

Constructor Details

StreamContentProducer

public StreamContentProducer()

Default constructor for creating a StreamContentProducer instance. Initializes the instance without specifying an output stream. The output stream will be set to null.

StreamContentProducer

public StreamContentProducer(OutputStream out)

Constructs a StreamContentProducer with the specified output stream. This constructor initializes the instance with the provided OutputStream and sets up a data listener to handle readiness notifications.

Parameters:

out - The output stream where the generated content will be written. Cannot be null.

Method Details

produce

public void produce()

Initiates the content production process and manages its lifecycle. This method ensures thread-safe execution by allowing only one thread to execute the critical section at a time. It prepares the output stream, retrieves the input content, generates the content, and finally, closes the output resources. In case of any error during the content generation or processing, it handles the exception by logging it and invoking the abort mechanism.

 The following describes the key stages in the process:
 - Thread-safe execution is ensured by synchronizing on the current object
   and checking the executing flag.
 - If the output stream has not been initialized, it retrieves it from
   the associated IO instance.
 - Content generation is initiated via the abstract `generateContent`
   method, which subclasses must implement to define specific content
   creation logic.
 - Resources are properly closed by invoking the `close` method.
 - On encountering a throwable, the exception is logged via the
   ApplicationServer, and the abort mechanism is triggered with the
   error details.
 

Note: Implementations of the abstract `generateContent` method must ensure that content is written to the 'out' stream. Thread starvation is mitigated by calling `Thread.yield()` if the current thread cannot acquire execution.

Specified by:

produce in interface ContentProducer

ready

public void ready()

Waits for the readiness signal, blocking the current thread until the condition is met. This method ensures that dependent threads can coordinate their execution based on the readiness state. It uses the `ready` CountDownLatch to manage synchronization. Any interruption of the waiting thread is caught and ignored, ensuring that the method continues operation without propagating the `InterruptedException`.

Specified by:

ready in interface ContentProducer

getFileName

public String getFileName()

Description copied from interface: ContentProducer

Retrieves the name of the file associated with the content.

Specified by:

getFileName in interface ContentProducer

Returns:

a String representing the name of the file, or null if the file name is unavailable.

generateContent

public abstract void generateContent()
                              throws Exception

Generate the content here and write to 'out'

Throws:

Exception - Can throw anything

getContent

public InputStream getContent()

Description copied from interface: ContentProducer

Retrieves the content as an InputStream.

Note: This may not invoke ContentProducer.produce() and it may just return the content if it is already available. It is implementation-dependent.

Specified by:

getContent in interface ContentProducer

Returns:

an InputStream representing the content. This may be null if the content is not yet available.

setTransactionManager

public void setTransactionManager(TransactionManager tm)

Description copied from interface: RequiresTransactionManager

Sets the transaction manager for this object. The transaction manager is responsible for managing transaction boundaries.

Specified by:

setTransactionManager in interface RequiresTransactionManager

Parameters:

tm - the transaction manager to be set

getTransactionManager

public TransactionManager getTransactionManager()

Description copied from interface: RequiresTransactionManager

Retrieves the transaction manager associated with this object.

Specified by:

getTransactionManager in interface ContentProducer

Specified by:

getTransactionManager in interface RequiresTransactionManager

Returns:

the transaction manager responsible for managing transaction boundaries

getWriter

protected Writer getWriter()

close

public void close()

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

abort

public void abort(Throwable error)

Description copied from interface: ContentProducer

This method may be called when the content generation is aborted due to some error.

Note: This could be invoked multiple times.

Specified by:

abort in interface ContentProducer

Parameters:

error - Error.

getError

public Throwable getError()

Description copied from interface: ContentProducer

Get the current error (set via ContentProducer.abort(Throwable)).

Specified by:

getError in interface ContentProducer

Returns:

Current error, if any.

getReportFormat

public final ReportFormat getReportFormat()

Retrieves the report format configuration associated with the current transaction manager or entity context. If a transaction manager is available, the report format is obtained based on it. Otherwise, the report format is derived from the current entity.

Returns:

The report format associated with the current transaction manager if available, otherwise the report format associated with the current entity.

getEntity

public final Entity getEntity()

Description copied from interface: ContentProducer

Retrieves the Entity associated with the current context. This method internally checks for a SystemEntity using ContentProducer.getSystemEntity(), and if it exists, retrieves the corresponding Entity.

Specified by:

getEntity in interface ContentProducer

Returns:

an Entity object if a SystemEntity is available and associated with an Entity, or null if no such association exists.

isBlocked

public final boolean isBlocked(String type)

isBlocked

public static boolean isBlocked(ContentProducer contentProducer,
 String type)