Understanding Flow Control Statements

The IfStatement.of(Expression test, Statement thenBranch, Statement elseBranch) method creates a statement that, when executed, first evaluates the test expression. This expression must evaluate to a Boolean value. If it evaluates to true, then the thenBranch statement is executed; otherwise, the elseBranch statement is executed. The IfStatement.of(Expression test, Statement thenBranch) method is a variant for an empty "else" branch.

For example, the following sample task takes a number as input, then uses IfStatement to:

@Configuration
public class Tasks {
    @Bean
    public ScriptedTaskDescription evenOrOddTask() {
        ScriptedTaskDescription task = new ScriptedTaskDescription("evenOrOddTask", "Is that number even or odd?");
        VariableAccessExpression n = VariableAccessExpression.of("A number");
        NumericExpression zero = NumericExpression.ZERO;
        NumericExpression two = NumericExpression.of(2);
        task.getScript()
            .addStatement(AskInputStatement.of(n.getVariableName(), true, JobInputType.INTEGER))
            .addStatement(LogStatement.info(StringExpression.concat(StringExpression.of("Is "), n, StringExpression.of(" even or odd?"))))
            .addStatement(IfStatement.of(BooleanExpression.eq(NumericExpression.minus(n, NumericExpression.times(NumericExpression.divide(n, two), two)), zero),
                Block.of(
                    LogStatement.info(StringExpression.concat(n, StringExpression.of(" is even"))),
                    SetTaskOutputStatement.of("Even or odd?", StringExpression.of("even"))
                ),
                Block.of(
                    LogStatement.info(StringExpression.concat(n, StringExpression.of(" is odd"))),
                    SetTaskOutputStatement.of("Even or odd?", StringExpression.of("odd"))
                )));
        return task;
    }
}

The generated web client component for this task is the following:

EvenOrOdd

The RepeatStatement.of(String loopVariableName, Expression nbLoops, Statement... statements) method creates a statement that, when executed, first evaluates the nbLoops expression. This expression must evaluate to a number. Then the statements are executed as many times. If a variable name is provided as loopVariableName, a variable is set with this name to an increasing value on each loop execution, starting with one. If you do not need a loop index variable, you can pass null as the first argument to the of method.

For example, the following task takes a number as input, then uses RepeatStatement to compute its factorial; finally, it sets the task output to the result.

@Configuration
public class Tasks {
    @Bean
    public ScriptedTaskDescription factorialTask() {
        ScriptedTaskDescription task = new ScriptedTaskDescription("FactTask", "Factorial");
        VariableAccessExpression n = VariableAccessExpression.of("n");
        VariableAccessExpression fact = VariableAccessExpression.of("n!");
        VariableAccessExpression index = VariableAccessExpression.of("index");

        task.getScript()
            .addStatement(AskInputStatement.of(n.getVariableName(), true, JobInputType.INTEGER, "The number to compute the factorial of"))
            .addStatement(SetVariableStatement.of(fact.getVariableName(), NumericExpression.ONE))
            .addStatement(RepeatStatement.of(index.getVariableName(), n,
                SetVariableStatement.of(fact.getVariableName(), NumericExpression.times(fact, index))))
            .addStatement(SetTaskOutputStatement.of("result", fact));
        return task;
    }
}

Here is an example of job computing 4! = 24.

4! = 24

The ForeachStatement.of(String elementVariableName, Expression elementsExpression, Statement... statements) method creates a statement that, when executed, first evaluates the elementsExpression expression. This expression must evaluate to a homogeneous list of values (they must all have the same type). Then for each element in that list, the statements are executed. If elementVariableName is not null, a variable with this name is set to the current list element during the execution of the statements. The breakOnError(boolean) method can be applied to a for-each statement to set the behavior of the loop if one of the statements in its body terminates with a non-zero exit code. When called with true, the loop will exit on the first (top-level) statement that exits/terminates with a non-zero exit code. When called with false (the default), exit codes do not influence the loop. In all cases, the exit code of the loop is the one of the last executed statement.

The NoopStatement.ok() method creates a statement that, when executed, terminates immediately with exit code zero.

The NoopStatement.withExitCode(Expression) method creates a statement that, when executed, terminates immediately with the value of the provided expression as its exit code. It terminates with an exception if this expression does not evaluate to a number.

NumericExpression.LAST_STATEMENT_EXIT_CODE is a numeric expression that, when evaluated, provides the value of the exit code of the last executed statement.

Statement.OK_EXIT_CODE is a numeric expression that, when evaluated, yields the exit code of " everything ok", that is, zero.

BooleanExpression.LAST_STATEMENT_EXIT_CODE_OK and BooleanExpression.LAST_STATEMENT_EXIT_CODE_NOT_OK are Boolean expressions that, when evaluated, return respectively "true" or "false" if the exit code of the last executed statement is, respectively, zero or non-zero.