transformerutils.java

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     * @throws IllegalArgumentException if the transformers collection is null
     * @throws IllegalArgumentException if any transformer in the collection is null
     */
    public static Transformer chainedTransformer(Collection transformers) {
        return ChainedTransformer.getInstance(transformers);
    }

    /**
     * Create a new Transformer that calls one of two transformers depending 
     * on the specified predicate.
     * 
     * @see org.apache.commons.collections.functors.SwitchTransformer
     * 
     * @param predicate  the predicate to switch on
     * @param trueTransformer  the transformer called if the predicate is true
     * @param falseTransformer  the transformer called if the predicate is false
     * @return the transformer
     * @throws IllegalArgumentException if the predicate is null
     * @throws IllegalArgumentException if either transformer is null
     */
    public static Transformer switchTransformer(Predicate predicate, Transformer trueTransformer, Transformer falseTransformer) {
        return SwitchTransformer.getInstance(new Predicate[] { predicate }, new Transformer[] { trueTransformer }, falseTransformer);
    }

    /**
     * Create a new Transformer that calls one of the transformers depending 
     * on the predicates. The transformer at array location 0 is called if the
     * predicate at array location 0 returned true. Each predicate is evaluated
     * until one returns true. If no predicates evaluate to true, null is returned.
     * 
     * @see org.apache.commons.collections.functors.SwitchTransformer
     * 
     * @param predicates  an array of predicates to check
     * @param transformers  an array of transformers to call
     * @return the transformer
     * @throws IllegalArgumentException if the either array is null
     * @throws IllegalArgumentException if the either array has 0 elements
     * @throws IllegalArgumentException if any element in the arrays is null
     * @throws IllegalArgumentException if the arrays are different sizes
     */
    public static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers) {
        return SwitchTransformer.getInstance(predicates, transformers, null);
    }

    /**
     * Create a new Transformer that calls one of the transformers depending 
     * on the predicates. The transformer at array location 0 is called if the
     * predicate at array location 0 returned true. Each predicate is evaluated
     * until one returns true. If no predicates evaluate to true, the default
     * transformer is called. If the default transformer is null, null is returned.
     * 
     * @see org.apache.commons.collections.functors.SwitchTransformer
     * 
     * @param predicates  an array of predicates to check
     * @param transformers  an array of transformers to call
     * @param defaultTransformer  the default to call if no predicate matches, null means return null
     * @return the transformer
     * @throws IllegalArgumentException if the either array is null
     * @throws IllegalArgumentException if the either array has 0 elements
     * @throws IllegalArgumentException if any element in the arrays is null
     * @throws IllegalArgumentException if the arrays are different sizes
     */
    public static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer) {
        return SwitchTransformer.getInstance(predicates, transformers, defaultTransformer);
    }

    /**
     * Create a new Transformer that calls one of the transformers depending 
     * on the predicates. 
     * <p>
     * The Map consists of Predicate keys and Transformer values. A transformer 
     * is called if its matching predicate returns true. Each predicate is evaluated
     * until one returns true. If no predicates evaluate to true, the default
     * transformer is called. The default transformer is set in the map with a 
     * null key. If no default transformer is set, null will be returned in a default
     * case. The ordering is that of the iterator() method on the entryset collection 
     * of the map.
     * 
     * @see org.apache.commons.collections.functors.SwitchTransformer
     * 
     * @param predicatesAndTransformers  a map of predicates to transformers
     * @return the transformer
     * @throws IllegalArgumentException if the map is null
     * @throws IllegalArgumentException if the map is empty
     * @throws IllegalArgumentException if any transformer in the map is null
     * @throws ClassCastException  if the map elements are of the wrong type
     */
    public static Transformer switchTransformer(Map predicatesAndTransformers) {
        return SwitchTransformer.getInstance(predicatesAndTransformers);
    }

    /**
     * Create a new Transformer that uses the input object as a key to find the
     * transformer to call. 
     * <p>
     * The Map consists of object keys and Transformer values. A transformer 
     * is called if the input object equals the key. If there is no match, the
     * default transformer is called. The default transformer is set in the map
     * using a null key. If no default is set, null will be returned in a default case.
     * 
     * @see org.apache.commons.collections.functors.SwitchTransformer
     * 
     * @param objectsAndTransformers  a map of objects to transformers
     * @return the transformer
     * @throws IllegalArgumentException if the map is null
     * @throws IllegalArgumentException if the map is empty
     * @throws IllegalArgumentException if any transformer in the map is null
     */
    public static Transformer switchMapTransformer(Map objectsAndTransformers) {
        Transformer[] trs = null;
        Predicate[] preds = null;
        if (objectsAndTransformers == null) {
            throw new IllegalArgumentException("The object and transformer map must not be null");
        }
        Transformer def = (Transformer) objectsAndTransformers.remove(null);
        int size = objectsAndTransformers.size();
        trs = new Transformer[size];
        preds = new Predicate[size];
        int i = 0;
        for (Iterator it = objectsAndTransformers.entrySet().iterator(); it.hasNext();) {
            Map.Entry entry = (Map.Entry) it.next();
            preds[i] = EqualPredicate.getInstance(entry.getKey());
            trs[i] = (Transformer) entry.getValue();
            i++;
        }
        return switchTransformer(preds, trs, def);
    }

    /**
     * Gets a Transformer that expects an input Class object that it will instantiate.
     * 
     * @see org.apache.commons.collections.functors.InstantiateTransformer
     * 
     * @return the transformer
     */
    public static Transformer instantiateTransformer() {
        return InstantiateTransformer.NO_ARG_INSTANCE;
    }

    /** 
     * Creates a Transformer that expects an input Class object that it will 
     * instantiate. The constructor used is determined by the arguments specified
     * to this method.
     *
     * @see org.apache.commons.collections.functors.InstantiateTransformer
     * 
     * @param paramTypes  parameter types for the constructor, can be null
     * @param args  the arguments to pass to the constructor, can be null
     * @return the transformer
     * @throws IllegalArgumentException if the paramTypes and args don't match
     */
    public static Transformer instantiateTransformer(Class[] paramTypes, Object[] args) {
        return InstantiateTransformer.getInstance(paramTypes, args);
    }

    /** 
     * Creates a Transformer that uses the passed in Map to transform the input 
     * object (as a simple lookup).
     *
     * @see org.apache.commons.collections.functors.MapTransformer
     * 
     * @param map  the map to use to transform the objects
     * @return the transformer
     * @throws IllegalArgumentException if the map is null
     */
    public static Transformer mapTransformer(Map map) {
        return MapTransformer.getInstance(map);
    }

    /**
     * Gets a Transformer that invokes a method on the input object.
     * The method must have no parameters. If the input object is null, 
     * null is returned.
     * <p>
     * For example, <code>TransformerUtils.invokerTransformer("getName");</code>
     * will call the <code>getName/code> method on the input object to 
     * determine the transformer result.
     * 
     * @see org.apache.commons.collections.functors.InvokerTransformer
     * 
     * @param methodName  the method name to call on the input object, may not be null
     * @return the transformer
     * @throws IllegalArgumentException if the methodName is null.
     */
    public static Transformer invokerTransformer(String methodName){
        return InvokerTransformer.getInstance(methodName, null, null);
    }

    /**
     * Gets a Transformer that invokes a method on the input object.
     * The method parameters are specified. If the input object is null, 
     * null is returned.
     * 
     * @see org.apache.commons.collections.functors.InvokerTransformer
     * 
     * @param methodName  the name of the method
     * @param paramTypes  the parameter types
     * @param args  the arguments
     * @return the transformer
     * @throws IllegalArgumentException if the method name is null
     * @throws IllegalArgumentException if the paramTypes and args don't match
     */
    public static Transformer invokerTransformer(String methodName, Class[] paramTypes, Object[] args){
        return InvokerTransformer.getInstance(methodName, paramTypes, args);
    }

    /**
     * Gets a transformer that returns a <code>java.lang.String</code>
     * representation of the input object. This is achieved via the
     * <code>toString</code> method, <code>null</code> returns 'null'.
     * 
     * @see org.apache.commons.collections.functors.StringValueTransformer
     * 
     * @return the transformer
     */
    public static Transformer stringValueTransformer() {
        return StringValueTransformer.INSTANCE;
    }
    
}