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Invoker

Although Java has very powerful runtime type information (RTTI) I've found it awkward to use. A particular case in point was trying to set parameters on a JDBC Datasource Object from a configuration file. The Invoker static class, below can be used to easily set properties on any class, given the object, property name and desired value.

package uk.org.codex.utils.rtti;

import java.lang.reflect.Method;

/*******************************************************************************
 * Static class designed to make setting properties easier from properties files 
 * or XML. It allows strings to be passed as parameter values for all basic 
 * types.
 * @author Ian A. Newby
 ******************************************************************************/
public class Invoker {
    
    /** Creates a new instance of Invoker */
    private Invoker() {
    }
    
    
    /***************************************************************************
     * Creates an object of an appropriate type to use in an invoke method.
     * @param val The value to convert
     * @param type The type required
     * @return 
     **************************************************************************/
    protected static Object convertArg(String val, Class type) {
        
        if (val == null) 
            return null;
        String v = val.trim();
        if (String.class.isAssignableFrom(type)) {
            return val;
        } else if (Integer.TYPE.isAssignableFrom(type)) {
            return new Integer(v);
        } else if (Long.TYPE.isAssignableFrom(type)) {
            return new Long(v);
        } else if (Boolean.TYPE.isAssignableFrom(type)) {
            if ("true".equalsIgnoreCase(v)) {
                return Boolean.TRUE;
            } else if ("false".equalsIgnoreCase(v)) {
                return Boolean.FALSE;
            }
        }
        return null;
    }
    
    /***************************************************************************
     * This static method allows a property to be set. It adds 'set' to the 
     * paramName passed in and invokes a method of that name.
     * @param object The object on which to set the param.
     * @param paramName The name of the parameter to set
     * @param value The value to set the parameter to.
     * @throws java.lang.Exception 
     **************************************************************************/
    public static void setProperty(Object object, String paramName, String value) throws Exception {
        
        Class cl = object.getClass();
        Class[] parameterTypes = new Class[] {};
        String methodName = "set" + paramName;
        Method method = null;
        Class paramType = null;
        Object arg = null;
        try {
            Method[] methods = cl.getMethods();
            for (int i=0; i< methods.length; i++) {
                if (methods[i].getName().equals(methodName)) {
                    Class[] params = methods[i].getParameterTypes();
                    if (params.length == 1) {
                        method = methods[i];
                        paramType = params[0];
                    }
                }
            }
            if (method != null) {
                try {
                    arg = convertArg(value, paramType);
                } catch (Throwable t) {
                    throw new Exception("Conversion to type ["+paramType + "] failed. Reason: "+t);
                }
                if (arg == null) {
                    throw new Exception("Conversion to type ["+paramType +"] failed.");
                }
                try {
                    method.invoke(object, new Object[]  { arg });
                } catch (Exception ex) {
                    try {
                        Exception e = new Exception(ex.getCause());
                        throw e;
                    } catch (Exception e) {
                        throw ex;
                    }
                }
            } else {
                throw new Exception("Method " + methodName + " not found");
            }
        } catch (Exception e) {
            throw new Exception(e);
        }
    }
}
 

Last updated: 12 Mar 2008 20:15:56