Chapter 144. HDFS Component (deprecated) Available as of Camel version 2.8 The hdfs component enables you to read and write messages from/to an HDFS file system. 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-hdfs</artifactId> <version>x.x.x</version> <!-- use the same version as your Camel core version --> </dependency> 144.1. URI format hdfs://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. Note 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. 144.2. Options The HDFS component supports 2 options, which are listed below. Name Description Default Type jAASConfiguration (common) To use the given configuration for security with JAAS. Configuration resolveProperty Placeholders (advanced) Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders. true boolean The HDFS endpoint is configured using URI syntax: with the following path and query parameters: 144.2.1. Path Parameters (3 parameters): Name Description Default Type hostName Required HDFS host to use String port HDFS port to use 8020 int path Required The directory path to use String 144.2.2. Query Parameters (38 parameters): Name Description Default Type connectOnStartup (common) 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. true boolean fileSystemType (common) Set to LOCAL to not use HDFS but local java.io.File instead. HDFS HdfsFileSystemType fileType (common) The file type to use. For more details see Hadoop HDFS documentation about the various files types. NORMAL_FILE HdfsFileType keyType (common) The type for the key in case of sequence or map files. NULL WritableType owner (common) The file owner must match this owner for the consumer to pickup the file. Otherwise the file is skipped. String valueType (common) The type for the key in case of sequence or map files BYTES WritableType bridgeErrorHandler (consumer) 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 or ERROR level and ignored. false boolean delay (consumer) The interval (milliseconds) between the directory scans. 1000 long initialDelay (consumer) For the consumer, how much to wait (milliseconds) before to start scanning the directory. long pattern (consumer) The pattern used for scanning the directory * String sendEmptyMessageWhenIdle (consumer) If the polling consumer did not poll any files, you can enable this option to send an empty message (no body) instead. false boolean exceptionHandler (consumer) To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored. ExceptionHandler exchangePattern (consumer) Sets the exchange pattern when the consumer creates an exchange. ExchangePattern pollStrategy (consumer) 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. PollingConsumerPoll Strategy append (producer) Append to existing file. Notice that not all HDFS file systems support the append option. false boolean overwrite (producer) Whether to overwrite existing files with the same name true boolean blockSize (advanced) The size of the HDFS blocks 67108864 long bufferSize (advanced) The buffer size used by HDFS 4096 int checkIdleInterval (advanced) 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. 500 int chunkSize (advanced) When reading a normal file, this is split into chunks producing a message per chunk. 4096 int compressionCodec (advanced) The compression codec to use DEFAULT HdfsCompressionCodec compressionType (advanced) The compression type to use (is default not in use) NONE CompressionType openedSuffix (advanced) When a file is opened for reading/writing the file is renamed with this suffix to avoid to read it during the writing phase. opened String readSuffix (advanced) Once the file has been read is renamed with this suffix to avoid to read it again. read String replication (advanced) The HDFS replication factor 3 short splitStrategy (advanced) 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 String synchronous (advanced) Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported). false boolean backoffErrorThreshold (scheduler) The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in. int backoffIdleThreshold (scheduler) The number of subsequent idle polls that should happen before the backoffMultipler should kick-in. int backoffMultiplier (scheduler) 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 actual attempt is happening again. When this option is in use then backoffIdleThreshold and/or backoffErrorThreshold must also be configured. int greedy (scheduler) If greedy is enabled, then the ScheduledPollConsumer will run immediately again, if the run polled 1 or more messages. false boolean runLoggingLevel (scheduler) The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that. TRACE LoggingLevel scheduledExecutorService (scheduler) Allows for configuring a custom/shared thread pool to use for the consumer. By default each consumer has its own single threaded thread pool. ScheduledExecutor Service scheduler (scheduler) To use a cron scheduler from either camel-spring or camel-quartz2 component none ScheduledPollConsumer Scheduler schedulerProperties (scheduler) To configure additional properties when using a custom scheduler or any of the Quartz2, Spring based scheduler. Map startScheduler (scheduler) Whether the scheduler should be auto started. true boolean timeUnit (scheduler) Time unit for initialDelay and delay options. MILLISECONDS TimeUnit useFixedDelay (scheduler) Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details. true boolean 144.3. Spring Boot Auto-Configuration The component supports 3 options, which are listed below. Name Description Default Type camel.component.hdfs.enabled Enable hdfs component true Boolean camel.component.hdfs.j-a-a-s-configuration To use the given configuration for security with JAAS. The option is a javax.security.auth.login.Configuration type. String camel.component.hdfs.resolve-property-placeholders Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders. true Boolean 144.3.1. 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. 144.4. 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 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: hdfs://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. 144.5. Message Headers The following headers are supported by this component: 144.5.1. 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. 144.6. 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. 144.7. 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.

Commands:
<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>
hdfs://hostname[:port][/path][?options]
hdfs:hostName:port/path
hdfs://localhost/tmp/simple-file?splitStrategy=IDLE:1000,BYTES:5