JSF 2.x Tip of the Day: Programmatically Creating EL MethodExpression

A common need is to create a MethodExpression for use in binding a JSF component action, or actionListener attributes to a value in the JSF/CDI managed beans.

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/**  * This is a convenience method that parses an expression into a  * {@link MethodExpression} for later evaluation. Use this method for  * expressions that refer to methods. If the expression is a {@code String}  * literal, a {@link MethodExpression} is created, which when invoked,  * returns the {@code String} literal, coerced to expectedReturnType. An  * {@link ELException} is thrown if expectedReturnType is {@code void} or if  * the coercion of the {@code String} literal to the expectedReturnType  * yields an error. This method should perform syntactic validation of the  * expression. If in doing so it detects errors, it should raise an  * {@link ELException}.  *  * @param methodExpression The expression to parse.  * @param expectedReturnType The expected return type for the method to be  * found. After evaluating the expression, the {@link MethodExpression} must  * check that the return type of the actual method matches this type.  * Passing in a value of {@code null} indicates the caller does not care  * what the return type is, and the check is disabled.  * @param expectedParamTypes The expected parameter types for the method to  * be found. Must be an array with no elements if there are no parameters  * expected. It is illegal to pass {@code null}, unless the method is  * specified with arguments in the EL expression, in which case these  * arguments are used for method selection, and this parameter is ignored.  * @return The parsed expression.  */ public static MethodExpression createMethodExpression(String methodExpression, Class<?> expectedReturnType, Class<?>[] expectedParamTypes) {     FacesContext context = FacesContext.getCurrentInstance();     return context.getApplication().getExpressionFactory()             .createMethodExpression(context.getELContext(), methodExpression, expectedReturnType, expectedParamTypes); }

Here is an example of how to use the method. In the example below I use both a ValueExpression and a MethodExpression for clarity. The MethodExpression is bound to a method called sort() in the IndexBean. Since this is bound to the action on the UICommandLink, it is expected that a String is returned which is used for determining navigation. Also note that an empty new Class[]{} array is passed as the expected parameter type.

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UICommandLink clink = (UICommandLink) application.createComponent(UICommandLink.COMPONENT_TYPE); clink.setValueExpression("value", createValueExpression("#{indexBean.columnHeader}", String.class)); clink.setActionExpression(createMethodExpression("#{indexBean.sort()}", String.class, new Class<?>[]{}));