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6.8

Java Reflection Invoking methods with primitive data types

Asked by dolphin_g in Java Standard Edition, JAXP & SAX (XML APIs), Java Programming Language, Extensible Markup Language (XML)

Tags: Java, reflection, xml

Hi,

I'm trying to write an application to run on app startup to lad values from XML file to
static java members. When I try to invoke a static java method with a primitive boolean
as  parameter it fails with the below stacktrace.

Root element of the doc is configuration
Total no of classes : 3
Class Name : com.tsswireless.application.dispatch.config.SpeedMatrixConfiguration
Variable :refPointX value :31.14 type :java.lang.Double
setRefPointX
Variable :refPointY value :108.36 type :java.lang.Double
setRefPointY
Variable :speedMatrixID value :01 type :java.lang.String
setSpeedMatrixID
Class Name : com.tsswireless.application.dispatch.config.CacheConfiguration
Variable :addressInfoFlag value :1 type :boolean
java.lang.NullPointerException
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:585)
      at com.tsswireless.application.dispatch.config.LoadConfiguration.main(LoadConfiguration.java:83)

The XML file is :

<?xml version="1.0" encoding="UTF-8"?>

<configuration>
      <class>
            <name>com.tsswireless.application.dispatch.config.SpeedMatrixConfiguration</name>
            <variable>
                  <name>refPointX</name>
                  <value>31.14</value>
                  <type>java.lang.Double</type>
            </variable>
            <variable>
                  <name>refPointY</name>
                  <value>108.36</value>
                  <type>java.lang.Double</type>
            </variable>
            <variable>
                  <name>speedMatrixID</name>
                  <value>01</value>
                  <type>java.lang.String</type>
            </variable>
      </class>
      <class>
            <name>com.tsswireless.application.dispatch.config.CacheConfiguration</name>
            <variable>
                  <name>addressInfoFlag</name>
                  <value>1</value>
                  <type>boolean</type>
            </variable>
            <variable>
                  <name>loadInfoFlag</name>
                  <value>1</value>
                  <type>boolean</type>
            </variable>
      </class>            
      <class>
            <name>com.tsswireless.application.dispatch.config.CostParameterConfiguration</name>
            <variable>
                  <name>directDistanceRatio</name>
                  <value>23.45</value>
                  <type>java.lang.Double</type>
            </variable>
      </class>
</configuration>

How do I resolve this? Also, is this the best way to do it? I'm trying to dynamically load values from the XML file. With this approach just creatign the java classes
and mentioning the package path should be good enough to load the values into the app.

Thanks,
Raja 
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/**
 * 
 */
package com.tsswireless.application.dispatch.config;
 
import java.io.File;
import java.lang.reflect.Method;
 
import org.w3c.dom.*;
 
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException; 
 
/**
 * <strong>LoadConfiguration</strong>, loads configuration parameters from StateManagerConfig.xml to its appropriate 
 * Class files.
 * 
 * @author Rama
 *
 */
public class LoadConfiguration {
 
	    public static void main (String argv []){
	    try {
 
	            DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
	            DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
	            Document doc = docBuilder.parse (new File("conf/StateManagerConfig.xml"));
 
	            // normalize text representation
	            doc.getDocumentElement ().normalize ();
	            System.out.println ("Root element of the doc is " + 
	                 doc.getDocumentElement().getNodeName());
 
 
	            NodeList classList = doc.getElementsByTagName("class");
	            int totalNoOfClasses = classList.getLength();
	            System.out.println("Total no of classes : " + totalNoOfClasses);
 
	            for(int s=0; s<classList.getLength() ; s++){
 
	                Node classNode = classList.item(s);
	                if(classNode.getNodeType() == Node.ELEMENT_NODE){
	                	
	                    Element classElement = (Element)classNode;
 
	                    //-------
	                    NodeList nameList = classElement.getElementsByTagName("name");
	                    Element classNameElement = (Element)nameList.item(0);
 
	                    String className = ((Node)classNameElement.getChildNodes().item(0)).getNodeValue().trim();
	                    System.out.println("Class Name : " + className );
	                    
	                    NodeList variableList = classElement.getElementsByTagName("variable");
	                    for(int i=0;i<variableList.getLength();i++){
	                    	Element variableElement = (Element)variableList.item(i);
	                    	NodeList variableNameList = variableElement.getElementsByTagName("name");
	                    	String variableNameElement = ((Node)variableNameList.item(0).getChildNodes().item(0)).getNodeValue().trim();
	                    	
	                    	NodeList variableValueList = variableElement.getElementsByTagName("value");
	                    	String variableValueElement = ((Node)variableValueList.item(0).getChildNodes().item(0)).getNodeValue().trim();
	                    	
	                    	NodeList variableTypeList = variableElement.getElementsByTagName("type");
	                    	String variableTypeElement = ((Node)variableTypeList.item(0).getChildNodes().item(0)).getNodeValue().trim();
	                    	
	                    	System.out.println("Variable :"+variableNameElement+ " value :"+variableValueElement
	                    			+" type :"+variableTypeElement);
	                    	
	                    	Class classtype = ClassLoader.getSystemClassLoader().loadClass(className);
	                    	
	                    	Method method1 = classtype.getMethod("set"+ variableNameElement.substring(0, 1).toUpperCase() +
		                    		variableNameElement.substring(1,variableNameElement.length()), getObjectType(variableTypeElement));
	                    	
	                    	if(variableTypeElement.equalsIgnoreCase("boolean")){
	                    		boolean value = false; 
	                    		if(variableValueElement.equals("true") || variableValueElement.equals("false")){
	            	    			value = variableValueElement.equalsIgnoreCase("true")?true:false;
	            	    		} else {
	            	    			value = variableValueElement.equalsIgnoreCase("1")?true:false;
	            	    		} 
	                    		method1.invoke(null, value);
	                    	} else {
	                    		method1.invoke(null, convertToObject(variableTypeElement, variableValueElement));
	                    	}
	                    	
	                    	System.out.println(method1.getName());
	                    }
 
 
	                }//end of if clause
 
 
	            }//end of for loop with s var
 
 
	        } catch (SAXParseException err) {
		        System.out.println ("** Parsing error" + ", line " 
		             + err.getLineNumber () + ", uri " + err.getSystemId ());
		        System.out.println(" " + err.getMessage ());
	        } catch (SAXException e) {
		        Exception x = e.getException ();
		        ((x == null) ? e : x).printStackTrace ();
	        } catch (Throwable t) {
	            t.printStackTrace ();
	        }
	        //System.exit (0);
 
	    }//end of main
	    
	    private static Object convertToObject(String dataType, String value) throws ClassNotFoundException, InstantiationException, IllegalAccessException{
	    	
	    	Object obj = null;
	    	if(dataType.equals("boolean")){
	    		
	    	} else {
	    		Class temp = Class.forName(dataType);
	    		if(temp == Double.class){
	    			obj = Double.valueOf(value);
	    		} else if(temp == Integer.class){
	    			obj = Integer.valueOf(value);
	    		} else if(temp == Short.class){
	    			obj = Short.valueOf(value);
	    		} else if(temp == Long.class){
	    			obj = Long.valueOf(value);
	    		} else if(temp == Float.class){
	    			obj = Float.valueOf(value);
	    		} else if(temp == Character.class){
	    			obj = String.valueOf(value);
	    		} else if(temp == Byte.class){
	    			obj = Byte.valueOf(value);
	    		} else if(temp == String.class){
	    			return value;
	    		} else {
	    			throw new UnsupportedOperationException("Unsupported Data type conversion, Type :"+dataType);
	    		}
	    	}
	    	return obj;
	    }
	    
	    private static Class getObjectType(String javaDataType) throws ClassNotFoundException{
	    	if(javaDataType.equals("boolean")){
	    		return java.lang.Boolean.TYPE;
	    	} else if(javaDataType.equals("int")){
	    		return java.lang.Integer.TYPE;
	    	} else if(javaDataType.equals("char")){
	    		return java.lang.Character.TYPE;
	    	} else if(javaDataType.equals("byte")){
	    		return java.lang.Byte.TYPE;
	    	} else if(javaDataType.equals("short")){
	    		return java.lang.Short.TYPE;
	    	} else if(javaDataType.equals("long")){
	    		return java.lang.Long.TYPE;
	    	} else if(javaDataType.equals("float")){
	    		return java.lang.Float.TYPE;
	    	} else if(javaDataType.equals("double")){
	    		return java.lang.Double.TYPE;
	    	} else if(javaDataType.equals("void")){
	    		return java.lang.Void.TYPE;
	    	} else
	    		return Class.forName(javaDataType);
	    	
	    }
 
}
[+][-]08/18/09 07:24 AM, ID: 25123551Accepted Solution

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About this solution

Zones: Java Standard Edition, JAXP & SAX (XML APIs), Java Programming Language, Extensible Markup Language (XML)
Tags: Java, reflection, xml
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Solution Provided By: TimYates
Participating Experts: 1
Solution Grade: B
 
[+][-]08/18/09 07:09 AM, ID: 25123349Administrative Comment

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[+][-]08/18/09 12:30 PM, ID: 25126679Expert Comment

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