Initializing Instance Fields
There are three ways to initialize instance fields used in flowlets:
Using the default constructor;
Using the
initialize()method of the flowlets; andUsing
@Propertyannotations.
To initialize using a property annotation, simply annotate the field definition with @Property.
The following example demonstrates the convenience of using @Property in a WordFilter flowlet that filters out specific words:
| Code Block |
|---|
public static class WordFilter extends AbstractFlowlet {
private OutputEmitter<String> out;
@Property
private final String toFilterOut;
public WordFilter(String toFilterOut) {
this.toFilterOut = toFilterOut;
}
@ProcessInput()
public void process(String word) {
if (!toFilterOut.equals(word)) {
out.emit(word);
}
}
} |
The flowlet constructor is called with the parameter when the flow is configured:
| Code Block |
|---|
public static class WordCountFlow extends AbstractFlow {
@Override
public void configure() {
setName("WordCountFlow");
setDescription("Flow for counting words");
addFlowlet("Tokenizer", new Tokenizer());
addFlowlet("WordsFilter", new WordsFilter("the"));
addFlowlet("WordsCounter", new WordsCounter());
connectStream("text", "Tokenizer");
connect("Tokenizer", "WordsFilter");
connect("WordsFilter", "WordsCounter");
}
} |
At run-time, when the flowlet is started, a value is injected into the toFilterOut field.
Note: Field types that are supported using the @Property annotation are primitives, boxed types (such as an Integer), String, and enum.
Scanning Over Tables with Byte Array Keys
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