THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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HDFS
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Component
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Available
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as
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of
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Camel
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2.8
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The
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hdfs
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component
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enables
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you
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to
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read
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and
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write
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messages
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from/to
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an
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HDFS
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file
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system.
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HDFS
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is
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the
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distributed
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file
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system
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at
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the
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heart
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of
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Maven users will need to add the following dependency to their pom.xml for this component:
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|http://hadoop.apache.org]. Maven users will need to add the following dependency to their {{pom.xml}} for this component: {code:xml} <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-hdfs</artifactId> <version>x.x.x</version> <!-- use the same version as your Camel core version --> </dependency> {code} h3. URI format {code} |
URI format
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hdfs://hostname[:port][/path][?options]
{code}
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You
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can
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append
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query
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options
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to
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the
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URI
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in
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the
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following
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format,
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?option=value&option=value&...
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The
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path
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is
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treated
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in
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the
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following
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way:
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- as
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- a
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- consumer,
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- if
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- it's
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- a
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- file,
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- it
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- just
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- reads
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- the
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- file,
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- otherwise
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- if
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- it
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- represents
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- a
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- directory
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- it
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- scans
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- all
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- the
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- file
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- under
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- the
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- path
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- satisfying
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- the
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- configured
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- pattern.
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- All
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- the
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- files
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- under
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- that
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- directory
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- must
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- be
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- of
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- the
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- same
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- type.
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- as
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- a
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- producer,
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- if
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- at
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- least
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- one
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- split
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- strategy
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- is
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- defined,
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- the
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- path
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- is
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- considered
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- a
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- directory
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- and
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- under
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- that
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- directory
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- the
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- producer
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- creates
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- a
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- different
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- file
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- per
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- split named using the configured UuidGenerator.
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When consuming from hdfs 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
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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>,*
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where
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<ST>
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can
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be:
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- BYTES
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- a
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- new
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- file
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- is
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- created,
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- and
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- the
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- old
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- is
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- closed
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- when
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- the
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- number
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- of
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- written
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- bytes
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- is
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- more
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- than
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- <value>
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- MESSAGES
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- a
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- new
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- file
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- is
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- created,
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- and
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- the
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- old
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- is
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- closed
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- when
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- the
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- number
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- of
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- written
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- messages
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- is
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- more
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- than
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- <value>
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- IDLE
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- a
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- new
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- file
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- is
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- created,
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- and
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- the
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- old
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- is
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- closed
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- when
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- no
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- writing
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- happened
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- in
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- the
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- last
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- <value> milliseconds
| Note |
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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:
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milliseconds for example: {code} hdfs://localhost/tmp/simple-file?splitStrategy=IDLE:1000,BYTES:5 {code} |
it
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means:
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a
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new
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file
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is
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created
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either
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when
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it
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has
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been
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idle
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for
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more
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than
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1
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second
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or
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if
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more
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than
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5
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bytes
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have
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been
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written.
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So,
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running
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hadoop
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fs
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-ls
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/tmp/simple-file
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you'll see that multiple files have been created.
Message Headers
The following headers are supported by this component:
Producer only
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Controlling to close file stream
Available as of Camel 2.10.4
When using the HDFS 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
This component is fully functional in an OSGi environment, however, it requires some actions from the user. Hadoop uses the thread context class loader in order to load resources. Usually, the thread context classloader will be the bundle class loader of the bundle that contains the routes. So, 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 in your bundle root. That file can be found in the hadoop-common.jar.