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:
| Code Block | ||||
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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
| Code Block |
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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
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- named
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- using
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- the
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- configured
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- .
Options
| Wiki Markup |
|---|
h3. Options {div:class=confluenceTableSmall} || Name || Default Value || Description || | {{overwrite}} | {{true}} | The file can be overwritten | | {{append}} | {{false}} | Append to existing file. Notice that not all HDFS file systems support the append option. | | {{bufferSize}} | {{4096}} | The buffer size used by HDFS | | {{replication}} | {{3}} | The HDFS replication factor | | {{blockSize}} | {{67108864}} | The size of the HDFS blocks | | {{fileType}} | {{NORMAL_FILE}} | It can be SEQUENCE_FILE, MAP_FILE, ARRAY_FILE, or BLOOMMAP_FILE, see Hadoop | | {{fileSystemType}} | {{HDFS}} | It can be LOCAL for local filesystem | | {{keyType}} | {{NULL}} | The type for the key in case of sequence or map files. See below. | | {{valueType}} | {{TEXT}} | The type for the key in case of sequence or map files. See below. | | {{splitStrategy}} | | A string describing the strategy on how to split the file based on different criteria. See below. | | {{openedSuffix}} | {{opened}} | 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}} | {{read}} | Once the file has been read is renamed with this suffix to avoid to read it again. | | {{initialDelay}} | {{0}} | For the consumer, how much to wait (milliseconds) before to start scanning the directory. | | {{delay}} | {{0}} | The interval (milliseconds) between the directory scans. | | {{pattern}} | {{*}} | The pattern used for scanning the directory | | {{chunkSize}} | {{4096}} | When reading a normal file, this is split into chunks producing a message per chunk. | | {{connectOnStartup}} | {{true}} | *Camel 2.9.3/2.10.1:* 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. | {div} h4. |
KeyType
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and
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ValueType
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- NULL
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- it
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- means
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- that
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- the
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- key
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- or
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- the
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- value
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- is
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- absent
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- BYTE
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- for
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- writing
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- a
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- byte,
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- the
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- java
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- Byte
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- class
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- is
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- mapped
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- into
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- a
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- BYTE
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- BYTES
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- for
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- writing
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- a
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- sequence
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- of
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- bytes.
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- It
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- maps
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- the
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- java
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- ByteBuffer
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- class
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- INT
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- for
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- writing
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- java
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- 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>
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- milliseconds
| Note |
|---|
note that this strategy currently requires either setting an IDLE value or setting the {note} note that this strategy currently requires either setting an IDLE value or setting theHdfsConstants.HDFS_CLOSE header to false to use the BYTES/MESSAGES configuration...otherwise, the file will be closed with each message |
for example:
| Code Block |
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message {note} 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
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see
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that
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multiple
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files
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have
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been
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created.
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Message
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Headers
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The
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following
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headers
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are
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supported
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by
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this
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component:
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Producer only
| Wiki Markup |
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only {div:class=confluenceTableSmall} || 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. | {div} h3. |
Controlling
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to
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close
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file
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stream
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Available
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as
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of
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Camel
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2.10.4
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When
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using
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the
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producer
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without
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a
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split
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strategy,
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then
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the
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file
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output
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stream
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is
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by
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default
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closed
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after
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the
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write.
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However
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you
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may
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want
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to
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keep
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the
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stream
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open,
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and
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only
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explicitly
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close
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the
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stream
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later.
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For
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that
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you
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can
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use
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the
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header
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HdfsConstants.HDFS_CLOSE
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(value
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=
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"CamelHdfsClose"
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)
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to
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control
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this.
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Setting
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this
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value
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to
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a
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boolean
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allows
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you
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to
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explicit
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control
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whether
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the
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stream
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should
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be
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closed
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or
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not.
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Notice
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this
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does
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not
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apply
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if
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you
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use
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a
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split
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strategy,
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as
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there
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are
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various
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strategies
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that
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can
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control
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when
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the
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stream
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is
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closed.
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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.