Spring batch xml to database

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XML Java Both. All batch processing can be described in its most simple form as reading in large amounts of data, performing some type of calculation or transformation, and writing the result out. Although a simple concept, an ItemReader is the means for providing data from many different types of input.

The most general examples include:. Flat File: Flat-file item readers read lines of data from a flat file that typically describes records with fields of data defined by fixed positions in the file or delimited by some special character such as a comma. Database: A database resource is accessed to return ets which can be mapped to objects for processing. The default SQL ItemReader implementations invoke a RowMapper to return objects, keep track of the current row if restart is required, store basic statistics, and provide some transaction enhancements that are explained later.

There are many more possibilities, but we focus on the basic ones for this chapter. A complete list of all available ItemReader implementations can be found in Appendix A. ItemReader is a basic interface for generic input operations, as shown in the following interface definition:. The read method defines the most essential contract of the ItemReader. Calling it returns one item or null if no more items are left.

An item might represent a line in a file, a row in a database, or an element in an XML file. It is generally expected that these are mapped to a usable domain object such as TradeFooor othersbut there is no requirement in the contract to do so. It is expected that implementations of the ItemReader interface are forward only. However, if the underlying resource is transactional such as a JMS queue then calling read may return the same logical item Spring batch xml to database subsequent calls in a rollback scenario. It is also worth noting that a lack of items to process by an ItemReader does not cause an exception to be thrown.

For example, a database ItemReader that is configured with a query that returns 0 returns null on the first invocation of read. ItemWriter is similar in functionality to an ItemReader but with inverse operations. Resources still need to be located, opened, and closed but they differ in that an ItemWriter writes out, rather than reading in. In the case of databases or queues, these operations may be inserts, updates, or sends. The format of the serialization of the output is specific to each batch Spring batch xml to database. As with ItemReaderItemWriter is a fairly generic interface, as shown in the following interface definition:.

As with read on ItemReaderwrite provides the basic contract of ItemWriter. It attempts to write out the list of items passed in as long as it is open. Because it is generally expected that items are 'batched' together into a chunk Spring batch xml to database then output, the interface accepts a list of items, rather than an item by itself. After writing out the list, any flushing that may be necessary can be performed before returning from the write method. For example, if writing to a Hibernate DAO, multiple calls to write can be made, one for each item.

The writer can then call flush on the hibernate session before returning. Both ItemReaders and ItemWriters serve their individual purposes well, but there is a common concern among both of them that necessitates another interface. In general, as part of the scope of a batch job, readers and writers need to be opened, closed, and require a mechanism for persisting state. The ItemStream interface serves that purpose, as shown in the following example:. Before describing each method, we should mention the ExecutionContext.

Clients of an ItemReader that also implement ItemStream should call open before any calls to readin order to open any resources such as files or to obtain connections. A similar restriction applies to an ItemWriter that implements ItemStream. As mentioned in Chapter 2, if expected data is found in the ExecutionContextit may be used to start the ItemReader or ItemWriter at a location other than its initial state. Conversely, close is called to ensure that any resources allocated during open are released safely.

This method is called before committing, to ensure that the current state is persisted in the database before commit. In the special case where the client of an ItemStream is a Step from the Spring Batch Corean ExecutionContext is created for each StepExecution to allow users to store the state of a particular execution, with the expectation that it is returned if the same JobInstance is started again.

Note that the CompositeItemWriter is an example of the delegation pattern, which is common in Spring Batch. The delegates themselves might implement callback interfaces, such as StepListener. If they do and if they are being used in conjunction with Spring Batch Core as part of a Step in a Jobthen they almost certainly need to be registered manually with the Step. A reader, writer, or processor that is directly wired into the Step gets registered automatically if it Spring batch xml to database ItemStream or a StepListener interface.

However, because the delegates are not known to the Stepthey need to be injected as listeners or streams or both if appropriate. One of the most common mechanisms for interchanging bulk data has always been the flat file. Unlike XML, which has an agreed upon standard for defining how it is structured XSDanyone reading a flat file must understand ahead of time exactly how the file is structured. In general, all flat files fall into two types: delimited and fixed length. Delimited files are those in which fields are Spring batch xml to database by a delimiter, such as a comma. Fixed Length files have fields that are a set length.

When working with flat files in Spring Batch, regardless of whether it is for input or output, one of the most important classes is the FieldSet. Many architectures and libraries contain abstractions for helping you read in from a file, but they usually return a String or an array of String objects.

This really only gets you halfway there. It allows developers to work with file input in much the same way as they would work with database input.

Spring batch xml to database

A FieldSet requires only one argument: a String array of tokens. Optionally, you can also configure the names of the fields so that the fields may be accessed either by index or name as patterned after etas shown in the following example:. The biggest advantage of the FieldSet is that it provides consistent parsing of flat file input. Rather than each batch job parsing differently in potentially unexpected ways, it can be consistent, both when handling errors caused by Spring batch xml to database format exception, or when doing simple data conversions.

A flat file is any type of file that contains at most two-dimensional tabular data. Reading flat files in the Spring Batch framework is facilitated by the class called FlatFileItemReaderwhich provides basic functionality for reading and parsing flat files. The LineMapper interface is explored more in the next sections.

The resource property represents a Spring Core Resource. Documentation explaining how to create beans of this type can be found in Spring Framework, Chapter 5. Therefore, this guide does not go into the details of creating Resource objects beyond showing the following simple example:.

Spring batch xml to database

In complex batch environments, the directory structures are often managed by the Enterprise Application Integration EAI infrastructure, where drop zones for external interfaces are established for moving files from FTP locations to batch processing locations and vice versa.

File moving utilities are beyond the scope of the Spring Batch architecture, but it is not unusual for batch job streams to include file moving utilities as steps in the job stream. The batch architecture only needs to know how to locate the files to be processed.

Spring Batch begins the process of feeding the data into the pipe from this starting point. However, Spring Integration provides many of these types of services. The other properties in FlatFileItemReader let you further specify how your data is interpreted, as described in the following table:. Specifies what text encoding to use. The default is the value of Charset.

Converts a String to an Object representing the item. Used to determine where the line endings are and do things like continue over a line ending if inside a quoted string. Interface that passes the raw line content of the lines in the file to be skipped. If linesToSkip is set to 2, then this interface is called twice.

In strict mode, the reader throws an exception on ExecutionContext if the input resource does not exist. Otherwise, it logs the problem and continues. As with RowMapperwhich takes a low-level construct such as et and returns an Objectflat file processing requires the same construct to convert a String line into an ObjectSpring batch xml to database shown in the following interface definition:.

The basic contract is that, given the current line and the line with which it is associated, the mapper should return a resulting domain object. This is similar to RowMapperin that each line is associated with its linejust as each row in a et is tied to its row.

This allows the line to be tied to the resulting domain object for identity comparison or for more informative logging. However, unlike RowMapperthe LineMapper is given a raw line which, as discussed above, only gets you halfway there. The line must be tokenized into a FieldSetwhich can then be mapped to an object, as described later in this document. An abstraction for turning a line of input into a FieldSet is necessary because there can be many formats of flat file data that need to be converted to a FieldSet.

In Spring Batch, this interface is the LineTokenizer :. The contract of a LineTokenizer is such that, given a line of Spring batch xml to database in theory the String could encompass more than one linea FieldSet representing the line is returned. Spring Batch contains the following LineTokenizer implementations:.

Spring batch xml to database

DelimitedLineTokenizer : Used for files where fields in a record are separated by a delimiter. The most common delimiter is a comma, but pipes or semicolons are often used as well. FixedLengthTokenizer : Used for files where fields in a record are each a "fixed Spring batch xml to database. The width of each field must be defined for each record type. PatternMatchingCompositeLineTokenizer : Determines which LineTokenizer among a list of tokenizers should be used on a particular line by checking against a pattern.

This object may be a custom DTO, a domain object, or an array, depending on the needs of the job. The FieldSetMapper is used in conjunction with Spring batch xml to database LineTokenizer to translate a line of data from a resource into an object of the desired type, as shown in the following interface definition:. Now that the basic interfaces for reading in flat files have been defined, it becomes clear that three basic steps are required:. The two interfaces described above represent two separate tasks: converting a line into a FieldSet and mapping a FieldSet to a domain object.

The DefaultLineMappershown in the following class definition, represents the behavior most users need:. The above functionality is provided in a default implementation, rather than being built into the reader itself as was done in versions of the framework to allow users greater flexibility in controlling the parsing process, especially if access to the raw line is needed.

The following example illustrates how to read a flat file with an actual domain scenario. This particular batch job re in football players from the following file:. To map a FieldSet into a Player object, a FieldSetMapper that returns players needs to be defined, as shown in the following example:.

Spring batch xml to database

The file can then be read by correctly constructing a FlatFileItemReader and calling readas shown in the following example:.

Spring batch xml to database

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