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Children's Ministry

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Aiden Jones
Aiden Jones

Download File Camel - I Can See Your House From...

Beware the JDK File IO API is a bit limited in detecting whether another application is currently writing/copying a file. And the implementation can be different depending on OS platform as well. This could lead to that Camel thinks the file is not locked by another process and start consuming it. Therefore you have to do you own investigation what suites your environment. To help with this Camel provides different readLock options and doneFileName option that you can use. See also the section Consuming files from folders where others drop files directly.

Download File Camel - I Can See Your House From...

A pluggable in-progress repository org.apache.camel.spi.IdempotentRepository. The in-progress repository is used to account the current in progress files being consumed. By default a memory based repository is used.

To use a custom org.apache.camel.spi.ExceptionHandler to handle any thrown exceptions that happens during the file on completion process where the consumer does either a commit or rollback. The default implementation will log any exception at WARN level and ignore.

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.

A pluggable org.apache.camel.component.file.GenericFileProcessStrategy allowing you to implement your own readLock option or similar. Can also be used when special conditions must be met before a file can be consumed, such as a special ready file exists. If this option is set then the readLock option does not apply.

Used by consumer, to only poll the files if it has exclusive read-lock on the file (i.e. the file is not in-progress or being written). Camel will wait until the file lock is granted. This option provides the build in strategies: - none - No read lock is in use - markerFile - Camel creates a marker file (fileName.camelLock) and then holds a lock on it. This option is not available for the FTP component - changed - Changed is using file length/modification timestamp to detect whether the file is currently being copied or not. Will at least use 1 sec to determine this, so this option cannot consume files as fast as the others, but can be more reliable as the JDK IO API cannot always determine whether a file is currently being used by another process. The option readLockCheckInterval can be used to set the check frequency. - fileLock - is for using java.nio.channels.FileLock. This option is not avail for Windows OS and the FTP component. This approach should be avoided when accessing a remote file system via a mount/share unless that file system supports distributed file locks. - rename - rename is for using a try to rename the file as a test if we can get exclusive read-lock. - idempotent - (only for file component) idempotent is for using a idempotentRepository as the read-lock. This allows to use read locks that supports clustering if the idempotent repository implementation supports that. - idempotent-changed - (only for file component) idempotent-changed is for using a idempotentRepository and changed as the combined read-lock. This allows to use read locks that supports clustering if the idempotent repository implementation supports that. - idempotent-rename - (only for file component) idempotent-rename is for using a idempotentRepository and rename as the combined read-lock. This allows to use read locks that supports clustering if the idempotent repository implementation supports that.Notice: The various read locks is not all suited to work in clustered mode, where concurrent consumers on different nodes is competing for the same files on a shared file system. The markerFile using a close to atomic operation to create the empty marker file, but its not guaranteed to work in a cluster. The fileLock may work better but then the file system need to support distributed file locks, and so on. Using the idempotent read lock can support clustering if the idempotent repository supports clustering, such as Hazelcast Component or Infinispan.

The move and preMove options are Expression-based, so we have the full power of the File Language to do advanced configuration of the directory and name pattern. Camel will, in fact, internally convert the directory name you enter into a File Language expression. So when we enter move=.done Camel will convert this into: $file:parent/.done/$file:onlyname. This is only done if Camel detects that you have not provided a $ in the option value yourself. So when you enter a $ Camel will not convert it and thus you have the full power.

The moveFailed option allows you to move files that could not be processed successfully to another location such as an error folder of your choice. For example to move the files in an error folder with a timestamp you can use moveFailed=/error/$file:name.noext-$date:now:yyyyMMddHHmmssSSS.$``file:ext.

If you omit the charset on the consumer endpoint, then Camel does not know the charset of the file, and would by default use "UTF-8". However you can configure a JVM system property to override and use a different default encoding with the key org.apache.camel.default.charset.

If you have some issues then you can enable DEBUG logging on org.apache.camel.component.file, and Camel logs when it reads/write a file using a specific charset. For example the route below will log the following:

When Camel is producing files (writing files) there are a few gotchas affecting how to set a filename of your choice. By default, Camel will use the message ID as the filename, and since the message ID is normally a unique generated ID, you will end up with filenames such as: ID-MACHINENAME-2443-1211718892437-1-0. If such a filename is not desired, then you must provide a filename in the CamelFileName message header. The constant, Exchange.FILE_NAME, can also be used.

Beware if you consume files from a folder where other applications write files to directly. Take a look at the different readLock options to see what suits your use cases. The best approach is however to write to another folder and after the write move the file in the drop folder. However if you write files directly to the drop folder then the option changed could better detect whether a file is currently being written/copied as it uses a file changed algorithm to see whether the file size / modification changes over a period of time. The other readLock options rely on Java File API that sadly is not always very good at detecting this. You may also want to look at the doneFileName option, which uses a marker file (done file) to signal when a file is done and ready to be consumed.

In this section we will use the file based idempotent repository org.apache.camel.processor.idempotent.FileIdempotentRepository instead of the in-memory based that is used as default. This repository uses a 1st level cache to avoid reading the file repository. It will only use the file repository to store the content of the 1st level cache. Thereby the repository can survive server restarts. It will load the content of the file into the 1st level cache upon startup. The file structure is very simple as it stores the key in separate lines in the file. By default, the file store has a size limit of 1mb. When the file grows larger Camel will truncate the file store, rebuilding the content by flushing the 1st level cache into a fresh empty file.

The option processStrategy can be used to use a custom GenericFileProcessStrategy that allows you to implement your own begin, commit and rollback logic. For instance lets assume a system writes a file in a folder you should consume. But you should not start consuming the file before another ready file has been written as well.

The filter option allows you to implement a custom filter in Java code by implementing the org.apache.camel.component.file.GenericFileFilter interface. This interface has an accept method that returns a boolean. Return true to include the file, and false to skip the file. There is a isDirectory method on GenericFile whether the file is a directory. This allows you to filter unwanted directories, to avoid traversing down unwanted directories.

If set this option to be true, camel-ftp will use the list file directly to check if the file exists. Since some FTP server may not support to list the file directly, if the option is false, camel-ftp will use the old way to list the directory and check if the file exists. This option also influences readLock=changed to control whether it performs a fast check to update file information or not. This can be used to speed up the process if the FTP server has a lot of files.

Configures whether resume download is enabled. This must be supported by the FTP server (almost all FTP servers support it). In addition the options localWorkDirectory must be configured so downloaded files are stored in a local directory, and the option binary must be enabled, which is required to support resuming of downloads.

Sets the download method to use when not using a local working directory. If set to true, the remote files are streamed to the route as they are read. When set to false, the remote files are loaded into memory before being sent into the route. If enabling this option then you must set stepwise=false as both cannot be enabled at the same time.

Whether to ignore when (trying to list files in directories or when downloading a file), which does not exist or due to permission error. By default when a directory or file does not exists or insufficient permission, then an exception is thrown. Setting this option to true allows to ignore that instead. 041b061a72


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