HDFS2 Component

Table of Contents

URI format
Options
Splitting Strategy
Message Headers
Controlling to close file stream
Using this component in OSGi

Available as of Camel 2.13

The hdfs2 component enables you to read and write messages from/to an HDFS file system using Hadoop 2.x. HDFS is the distributed file system at the heart of Hadoop.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-hdfs2</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

URI format

hdfs2://hostname[:port][/path][?options]

You can append query options to the URI in the following format, ?option=value&option=value&… The path is treated in the following way:

as a consumer, if it’s a file, it just reads the file, otherwise if it represents a directory it scans all the file under the path satisfying the configured pattern. All the files under that directory must be of the same type.
as a producer, if at least one split strategy is defined, the path is considered a directory and under that directory the producer creates a different file per split named using the configured UuidGenerator.

When consuming from hdfs2 then in normal mode, a file is split into chunks, producing a message per chunk. You can configure the size of the chunk using the chunkSize option. If you want to read from hdfs and write to a regular file using the file component, then you can use the fileMode=Append to append each of the chunks together.

Options

Table of Contents

KeyType and ValueType

The HDFS2 component supports 1 options which are listed below.

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Name	Java Type	Description
jAASConfiguration	`Configuration`	To use the given configuration for security with JAAS.

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The HDFS2 component supports 41 endpoint options which are listed below:

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Name	Group	Default	Java Type	Description
hostName	common		`String`	Required HDFS host to use
port	common	`8020`	`int`	HDFS port to use
path	common		`String`	Required The directory path to use
connectOnStartup	common	`true`	`boolean`	Whether to connect to the HDFS file system on starting the producer/consumer. If false then the connection is created on-demand. Notice that HDFS may take up till 15 minutes to establish a connection as it has hardcoded 45 x 20 sec redelivery. By setting this option to false allows your application to startup and not block for up till 15 minutes.
fileSystemType	common	`HDFS`	`HdfsFileSystemType`	Set to LOCAL to not use HDFS but local java.io.File instead.
fileType	common	`NORMAL_FILE`	`HdfsFileType`	The file type to use. For more details see Hadoop HDFS documentation about the various files types.
keyType	common	`NULL`	`WritableType`	The type for the key in case of sequence or map files.
owner	common		`String`	The file owner must match this owner for the consumer to pickup the file. Otherwise the file is skipped.
valueType	common	`BYTES`	`WritableType`	The type for the key in case of sequence or map files
bridgeErrorHandler	consumer	`false`	`boolean`	Allows for bridging the consumer to the Camel routing Error Handler which mean any exceptions occurred while the consumer is trying to pickup incoming messages or the likes will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions that will be logged at WARN/ERROR level and ignored.
delay	consumer	`1000`	`long`	The interval (milliseconds) between the directory scans.
initialDelay	consumer	`10000`	`long`	For the consumer how much to wait (milliseconds) before to start scanning the directory.
pattern	consumer	`*`	`String`	The pattern used for scanning the directory
sendEmptyMessageWhenIdle	consumer	`false`	`boolean`	If the polling consumer did not poll any files you can enable this option to send an empty message (no body) instead.
exceptionHandler	consumer (advanced)		`ExceptionHandler`	To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this options is not in use. By default the consumer will deal with exceptions that will be logged at WARN/ERROR level and ignored.
exchangePattern	consumer (advanced)		`ExchangePattern`	Sets the exchange pattern when the consumer creates an exchange.
pollStrategy	consumer (advanced)		`PollingConsumerPollStrategy`	A pluggable org.apache.camel.PollingConsumerPollingStrategy allowing you to provide your custom implementation to control error handling usually occurred during the poll operation before an Exchange have been created and being routed in Camel.
append	producer	`false`	`boolean`	Append to existing file. Notice that not all HDFS file systems support the append option.
overwrite	producer	`true`	`boolean`	Whether to overwrite existing files with the same name
blockSize	advanced	`67108864`	`long`	The size of the HDFS blocks
bufferSize	advanced	`4096`	`int`	The buffer size used by HDFS
checkIdleInterval	advanced	`500`	`int`	How often (time in millis) in to run the idle checker background task. This option is only in use if the splitter strategy is IDLE.
chunkSize	advanced	`4096`	`int`	When reading a normal file this is split into chunks producing a message per chunk.
compressionCodec	advanced	`DEFAULT`	`HdfsCompressionCodec`	The compression codec to use
compressionType	advanced	`NONE`	`CompressionType`	The compression type to use (is default not in use)
openedSuffix	advanced	`opened`	`String`	When a file is opened for reading/writing the file is renamed with this suffix to avoid to read it during the writing phase.
readSuffix	advanced	`read`	`String`	Once the file has been read is renamed with this suffix to avoid to read it again.
replication	advanced	`3`	`short`	The HDFS replication factor
splitStrategy	advanced		`String`	In the current version of Hadoop opening a file in append mode is disabled since it’s not very reliable. So for the moment it’s only possible to create new files. The Camel HDFS endpoint tries to solve this problem in this way: If the split strategy option has been defined the hdfs path will be used as a directory and files will be created using the configured UuidGenerator. Every time a splitting condition is met a new file is created. The splitStrategy option is defined as a string with the following syntax: splitStrategy=ST:valueST:value… where ST can be: BYTES a new file is created and the old is closed when the number of written bytes is more than value MESSAGES a new file is created and the old is closed when the number of written messages is more than value IDLE a new file is created and the old is closed when no writing happened in the last value milliseconds
synchronous	advanced	`false`	`boolean`	Sets whether synchronous processing should be strictly used or Camel is allowed to use asynchronous processing (if supported).
backoffErrorThreshold	scheduler		`int`	The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in.
backoffIdleThreshold	scheduler		`int`	The number of subsequent idle polls that should happen before the backoffMultipler should kick-in.
backoffMultiplier	scheduler		`int`	To let the scheduled polling consumer backoff if there has been a number of subsequent idles/errors in a row. The multiplier is then the number of polls that will be skipped before the next actual attempt is happening again. When this option is in use then backoffIdleThreshold and/or backoffErrorThreshold must also be configured.
greedy	scheduler	`false`	`boolean`	If greedy is enabled then the ScheduledPollConsumer will run immediately again if the previous run polled 1 or more messages.
runLoggingLevel	scheduler	`TRACE`	`LoggingLevel`	The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that.
scheduledExecutorService	scheduler		`ScheduledExecutorService`	Allows for configuring a custom/shared thread pool to use for the consumer. By default each consumer has its own single threaded thread pool.
scheduler	scheduler	`none`	`ScheduledPollConsumerScheduler`	To use a cron scheduler from either camel-spring or camel-quartz2 component
schedulerProperties	scheduler		`Map`	To configure additional properties when using a custom scheduler or any of the Quartz2 Spring based scheduler.
startScheduler	scheduler	`true`	`boolean`	Whether the scheduler should be auto started.
timeUnit	scheduler	`MILLISECONDS`	`TimeUnit`	Time unit for initialDelay and delay options.
useFixedDelay	scheduler	`true`	`boolean`	Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details.

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KeyType and ValueType

NULL it means that the key or the value is absent
BYTE for writing a byte, the java Byte class is mapped into a BYTE
BYTES for writing a sequence of bytes. It maps the java ByteBuffer class
INT for writing java integer
FLOAT for writing java float
LONG for writing java long
DOUBLE for writing java double
TEXT for writing java strings

BYTES is also used with everything else, for example, in Camel a file is sent around as an InputStream, int this case is written in a sequence file or a map file as a sequence of bytes.

Splitting Strategy

In the current version of Hadoop opening a file in append mode is disabled since it’s not very reliable. So, for the moment, it’s only possible to create new files. The Camel HDFS endpoint tries to solve this problem in this way:

If the split strategy option has been defined, the hdfs path will be used as a directory and files will be created using the configured UuidGenerator
Every time a splitting condition is met, a new file is created. The splitStrategy option is defined as a string with the following syntax: splitStrategy=<ST>:<value>,<ST>:<value>,*

where <ST> can be:

BYTES a new file is created, and the old is closed when the number of written bytes is more than <value>
MESSAGES a new file is created, and the old is closed when the number of written messages is more than <value>
IDLE a new file is created, and the old is closed when no writing happened in the last <value> milliseconds

note that this strategy currently requires either setting an IDLE value or setting the HdfsConstants.HDFS_CLOSE header to false to use the BYTES/MESSAGES configuration…otherwise, the file will be closed with each message

for example:

hdfs2://localhost/tmp/simple-file?splitStrategy=IDLE:1000,BYTES:5

it means: a new file is created either when it has been idle for more than 1 second or if more than 5 bytes have been written. So, running hadoop fs -ls /tmp/simple-file you’ll see that multiple files have been created.

Message Headers

Table of Contents

Producer only

The following headers are supported by this component:

Producer only

Header	Description
`CamelFileName`	Camel 2.13: Specifies the name of the file to write (relative to the endpoint path). The name can be a `String` or an Expression object. Only relevant when not using a split strategy.

Controlling to close file stream

When using the HDFS2 producer without a split strategy, then the file output stream is by default closed after the write. However you may want to keep the stream open, and only explicitly close the stream later. For that you can use the header HdfsConstants.HDFS_CLOSE (value = "CamelHdfsClose") to control this. Setting this value to a boolean allows you to explicit control whether the stream should be closed or not.

Notice this does not apply if you use a split strategy, as there are various strategies that can control when the stream is closed.

Using this component in OSGi

Table of Contents

Using this component with manually defined routes
Using this component with Blueprint container

There are some quirks when running this component in an OSGi environment related to the mechanism Hadoop 2.x uses to discover different org.apache.hadoop.fs.FileSystem implementations. Hadoop 2.x uses java.util.ServiceLoader which looks for /META-INF/services/org.apache.hadoop.fs.FileSystem files defining available filesystem types and implementations. These resources are not available when running inside OSGi.

As with camel-hdfs component, the default configuration files need to be visible from the bundle class loader. A typical way to deal with it is to keep a copy of core-default.xml (and e.g., hdfs-default.xml) in your bundle root.

Using this component with manually defined routes

There are two options:

Package /META-INF/services/org.apache.hadoop.fs.FileSystem resource with bundle that defines the routes. This resource should list all the required Hadoop 2.x filesystem implementations.
Provide boilerplate initialization code which populates internal, static cache inside org.apache.hadoop.fs.FileSystem class:

org.apache.hadoop.conf.Configuration conf = new org.apache.hadoop.conf.Configuration();
conf.setClass("fs.file.impl", org.apache.hadoop.fs.LocalFileSystem.class, FileSystem.class);
conf.setClass("fs.hdfs.impl", org.apache.hadoop.hdfs.DistributedFileSystem.class, FileSystem.class);
...
FileSystem.get("file:///", conf);
FileSystem.get("hdfs://localhost:9000/", conf);
...

Using this component with Blueprint container

Two options:

Package /META-INF/services/org.apache.hadoop.fs.FileSystem resource with bundle that contains blueprint definition.
Add the following to the blueprint definition file:

<bean id="hdfsOsgiHelper" class="org.apache.camel.component.hdfs2.HdfsOsgiHelper">
   <argument>
      <map>
         <entry key="file:///" value="org.apache.hadoop.fs.LocalFileSystem"  />
         <entry key="hdfs://localhost:9000/" value="org.apache.hadoop.hdfs.DistributedFileSystem" />
         ...
      </map>
   </argument>
</bean>

<bean id="hdfs2" class="org.apache.camel.component.hdfs2.HdfsComponent" depends-on="hdfsOsgiHelper" />

This way Hadoop 2.x will have correct mapping of URI schemes to filesystem implementations.