JavaBeanWriter

Home \| Table of Contents	JavaBeanWriter	CloverETL 4.7.0
Prev	Writers	Next

Short Description

JavaBeanWriter writes a hierarchical structure as JavaBeans into a dictionary. That allows dynamic data interchange between Clover graphs and external environment, such as cloud.

Depending on JavaBean you choose defines the output to a certain extent - that is why you map inputs to a pre-set but customizable tree structure. Also, you can write data to Java collections (Lists, Maps). When writing, JavaBeanWriter consults your bean's classpath to decide which data types to write. That means it performs type conversions between your metadata field types and JavaBeans types. If a conversion fails, you will experience errors on writing.

A number of classes is supported for writing.

If you are looking for a more flexible component which is less restrictive in terms of data types and requires no external classpath, choose JavaMapWriter.

Component	Data output	Input ports	Output ports	Each to all outputs	Different to different outputs	Transformation	Transf. req.	Java	CTL	Auto-propagated metadata
JavaBeanWriter	dictionary	1-n	0

Icon

Ports

Port type	Number	Required	Description	Metadata
Input	0-N	At least one	Input records to be joined and mapped to JavaBeans.	Any (each port can have different metadata)

JavaBeanWriter Attributes

Attribute	Req	Description	Possible values
Basic
Dictionary target	yes	The dictionary you want to write JavaBeans to.	Name of a dictionary you have previously defined.
Bean structure		Click the '...' button to design the structure of your output JavaBean consisting of custom classes, objects, collections or maps.	See Defining Bean Structure.
Mapping	^[1]	Defines how input data is mapped to output JavaBeans.	See Mapping Editor.
Mapping URL	^[1]	External text file containing the mapping definition.
Advanced
Cache size		A size of of the database used when caching data from ports to elements (the data is first processed then written). The larger your data is, the larger cache is needed to maintain fast processing.	auto (default) \| e.g. 300MB, 1GB etc.
Cache in Memory		Cache data records in memory instead of disk cache. Note that while it is possible to set maximal size of the cache for the disk cache, this setting is ignored in case in-memory-cache si used. As a result, an OutOfMemoryError may occur when caching too many data records.	true \| false (default)
Sorted input		Tells JavaBeanWriter whether the input data is sorted. Setting the attribute to true declares you want to use the sort order defined in Sort keys, see below.	false (default) \| true
Sort keys		Tells JavaBeanWriter how the input data is sorted, thus enabling streaming. The sort order of fields can be given for each port in a separate tab. Working with Sort keys has been described in Sort Key.
Max number of records		Maximum number of records written to output. See Selecting Output Records.	0-N
^[1] One of these has to be specified. If both are specified, Mapping URL has a higher priority.

Details

JavaBeanWriter receives data through all connected input ports and converts Clover records to JavaBean properties based on the mapping you define. At last, the resulting tree structure is written to a dictionary (which is the only possible output). Remember the component cannot write to a file.

The logic of mapping is similar to XMLWriter - if you are familiar with its mapping editor, you will have no problems designing the output tree in this component. The differences are:

you cannot map input to output freely - the design of the tree structure you can see in the mapping editor is determined by the JavaBean you are using
JavaBeanWriter allows you to map to Beans, their properties or collections - Lists, Maps
there are no attributes, wildcard attributes and wildcard elements as in XML

Defining Bean Structure

Before you can start mapping, you need to define contents of the output JavaBean. Start by editing the Bean structure attribute which opens this dialog:

Figure 54.8. Defining bean structure - click the Select combo box to start.

Java object - clicking it opens a dialog in which you can choose from Java classes. Important: if you intend to use a custom JavaBeans class, place it into the trans folder. The class will then be available in this dialog.
Collection - adds a list consisting of other objects, maps or other collections.
Map - adds a key-value map.

Mapping Editor

Having defined the bean structure, proceed to mapping input records to output JavaBeans. You perform that in a manner which is very close to what you already know from XMLWriter. Mapping editors in both components have similar logic.

The very basics of mapping are:

Edit the component's Mapping attribute. This will open the visual mapping editor:
Figure 54.9. Mapping editor in JavaBeanWriter after first open. Metadata on the input edge(s) are displayed on the left hand side. The right hand pane is where you design the desired output tree - it is pre-defined by your bean's structure (note: in the example, the bean contains employees and projects they are working on). Mapping is then performed by dragging metadata from left to right (and performing additional tasks described below).
In the right hand pane, you can map input metadata to:
- Beans
- Bean properties
- Lists
- Maps
Click the green '+' sign to Add entry. This adds a new item into the tree - its type depends on context (the node you have selected). Remember the button is not available every time as the output structure is determined by bean structure.
Connect input records to output nodes to create Binding.
Example 54.2. Creating Binding

Figure 54.10. Example mapping in JavaBeanWriter - employees are joined with projects they work on. Fields in bold (their content) will be printed to the output dictionary, i.e. they are used in the mapping.
At any time, you can switch to the Source tab and write/check the mapping yourself in code.
If the basic instructions found here were not satisfying, please consult XMLWriter's Details where the whole mapping process is described profusely.