Dependency injection with Wrapper classes

[John McParland]

Hi all,

I am fairly new to Spring and decided to use the little I'd learned about dependency injection to experiment!

However I cannot seem to configure/code spring to inject bean properties of wrapper classes, e.g. Double. See this;

Code;

package com.mcparland.john.conversion;

/**
 * Simple Spring dependency injection example to convert values based on a rate
 */
public class Simple {
    
    /**
     * The conversion rate
     */
    private double rate = 0.0d;
    
    /**
     * Set the conversion rate
     * @param rate The rate for conversion
     */
    public void setRate(Double rate)
    {
        this.rate = rate;
    }
    
    /**
     * Get the conversion rate
     * @return The rate for conversion
     */
    public double getRate()
    {
        return rate;
    }
    
    /**
     * Convert some value
     * @return the converted value
    */
    public double convert(Double value)
    {
        return value * rate;
    }
    
}

Main class

package com.mcparland.john.conversion;

/**
 * Main application for conversion
 */
public class ConverterApp {

    public static void printHelp() {
        System.out.println("ConverterApp <value>");
        System.out.println("<value> is the value to convert");
    }

    /**
     * Main program
     * 
     * @param args
     *            Program arguments, none required
     */
    public static void main(String[] args) {
        BeanFactory beans = new XmlBeanFactory(new FileSystemResource("config/Conversion.xml"));
        Simple  converter = (Simple) beans.getBean("simple");
        double miles = 7;
        if (1 == args.length) {
            try {
                miles = Integer.parseInt(args[0]);
                System.out.println(miles + " miles in km = " + converter.convert(miles));
            } catch (NumberFormatException nfe) {
                printHelp();
            }
        } else {
            printHelp();
        }
    }

}

Spring config
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- Simple conversion bean --> <bean id="simple" class="com.mcparland.john.conversion.Simple"> <property name="rate" value="1.609344"/> </bean> </beans>

When I run this, I get the following exception;

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'simple' defined in file [...\users\mcparlan\eclipse\projects\java\RunningTimeConversion\config\Conversion.xml]: Initialization of bean failed; nested exception is org.springframework.beans.TypeMismatchException: Failed to convert property value of type [java.lang.String] to required type [double] for property 'rate'; nested exception is java.lang.IllegalArgumentException: Method must not be null
Caused by: org.springframework.beans.TypeMismatchException: Failed to convert property value of type [java.lang.String] to required type [double] for property 'rate'; nested exception is java.lang.IllegalArgumentException: Method must not be null
Caused by: java.lang.IllegalArgumentException: Method must not be null
	at org.springframework.util.Assert.notNull(Assert.java:112)
	at org.springframework.core.MethodParameter.<init>(MethodParameter.java:78)
	at org.springframework.core.MethodParameter.<init>(MethodParameter.java:64)
	at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:138)
	at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:380)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1112)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:862)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:423)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:249)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:155)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:246)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:160)
	at com.mcparland.john.conversion.ConverterApp.main(ConverterApp.java:37)

Any ideas? Is it possible to inject wrapper types as properties?

Thanks,

John

[John McParland]

Typical, the second I post it, I find the bug!

The declaration of

  /** 
   * The conversion rate 
   */  
   private double rate = 0.0d;  

was changed to;

  /** 
   * The conversion rate 
   */  
   private Double rate = 0.0d;  

note the use of Double rather than double.

So this brings me to a second, similar problem. I have an interface;

package com.mcparland.john.conversion;

/**
 * Converts from one unit of measurement to another
 * <p>
 * Also provides the option to invert - this is to allow one class to manage all conversion between two units
 * of measurement, e.g. Miles and KM, so {@link #convert(T)} could do Miles to KM while {@link #invert(T)} would 
 * do KM to Miles
 * </p>
 */
public interface Converter<T> {

    /**
     * Set the conversion rate
     * @param rate The rate for conversion
     */
    public void setConversionRate(T rate);
    
    /**
     * Get the conversion rate
     * @return The rate for conversion
     */
    public T getConversionRate();
    
    /**
     * Get the rate of inversion
     * @return The inversion rate
     */
    public T getInversionRate();
    
    /**
     * Convert the given value to the new measurement
     * @param value The value to convert
     * @return The converted value
     */
    public T convert(T value);
    
    /**
     * Invert the value given (i.e. do the opposite of the conversion)
     * @param value The value to invert
     * @return The inverted value
     */
    public T invert(T value);
    
    /**
     * Set the name of the units converted from
     * @param convertFromUnitName The unit name converted from
     */
    public void setConvertFromUnitName(String convertFromUnitName);
    
    /**
     * Get the name of the units converted from
     * @return The unit name converted from
     */
    public String getConvertFromUnitName();
    
    /**
     * Set the name of the units converted to
     * @param convertToUnitName The unit name converted to
     */
    public void setConvertToUnitName(String convertToUnitName);
    
    /**
     * Get the name of the units converted to
     * @return The unit name converted to
     */
    public String getConvertToUnitName();
    
}

an implementing class;

package com.mcparland.john.conversion;

/**
 * Converts based on multiplication of a rate
 * 
 */
public class RateMultiplierConverter implements Converter<Double> {

    /**
     * The conversion rate
     */
    private Double conversionRate = 0.0d;

    /**
     * The inverted rate
     */
    private Double inversionRate = 0.0d;

    /**
     * The units converted from
     */
    private String convertFromUnitName = "";

    /**
     * The units converted to
     */
    private String convertToUnitName = "";

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#convert(java.lang.Double)
     */
    @Override
    public Double convert(Double value) {
        // The most precise this can be is a double, if greater is needed then clearly a different converter
        // is also
        return conversionRate.doubleValue() * value.doubleValue();
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#getConversionRate()
     */
    @Override
    public Double getConversionRate() {
        return conversionRate;
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#getConvertFromUnitName()
     */
    @Override
    public String getConvertFromUnitName() {
        return convertFromUnitName;
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#getConvertToUnitName()
     */
    @Override
    public String getConvertToUnitName() {
        return convertToUnitName;
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#getInversionRate()
     */
    @Override
    public Double getInversionRate() {
        return inversionRate;
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#invert(java.lang.Double)
     */
    @Override
    public Double invert(Double value) {
        return inversionRate.doubleValue() * value.doubleValue();
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#setConversionRate(java.lang.Double)
     */
    @Override
    public void setConversionRate(Double rate) {
        // TODO Auto-generated method stub
        this.conversionRate = rate;
        inversionRate = 1.0 / rate.doubleValue();
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#setConvertFromUnitName(java.lang.String)
     */
    @Override
    public void setConvertFromUnitName(String convertFromUnitName) {
        this.convertFromUnitName = convertFromUnitName;
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.mcparland.john.conversion.Converter#setConvertToUnitName(java.lang.String)
     */
    @Override
    public void setConvertToUnitName(String convertToUnitName) {
        this.convertToUnitName = convertToUnitName;
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#toString()
     */
    public String toString() {
        return "Convert from " + convertFromUnitName + " to " + convertToUnitName + " @ rate "+conversionRate;
    }

}

a main class

package com.mcparland.john.conversion;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.FileSystemResource;

/**
 * Main application for conversion
 */
public class ConverterApp {

    public static void printHelp() {
        System.out.println("ConverterApp <value>");
        System.out.println("<value> is the value to convert");
    }

    /**
     * Main program
     * 
     * @param args
     *            Program arguments, none required
     */
    public static void main(String[] args) {
        BeanFactory beans = new XmlBeanFactory(new FileSystemResource("config/Conversion.xml"));
        RateMultiplierConverter converter = (RateMultiplierConverter) beans.getBean("milesToKm");
        double miles = 7;
        if (1 == args.length) {
            try {
                miles = Integer.parseInt(args[0]);
                System.out.println(miles + " miles in km = " + converter.convert(miles));
            } catch (NumberFormatException nfe) {
                printHelp();
            }
        } else {
            printHelp();
        }
    }

}

and a Spring config;

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- UK Miles to Kilometres conversion --> <bean id="milesToKm" class="com.mcparland.john.conversion.RateMultiplierConverter"> <property name="conversionRate" value="1.609344"/> <property name="convertFromUnitName" value="UK Miles"/> <property name="convertToUnitName" value="Kilometres"/> </bean> </beans>

But when I try to run (e.g. java com.mcparland.john.conversion.ConverterApp 7) I get the following exception;

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'milesToKm' defined in file [\\msad\root\EU\EUBO\GC\users\mcparlan\eclipse\projects\java\RunningTimeConversion\config\Conversion.xml]: Error setting property values; nested exception is org.springframework.beans.PropertyBatchUpdateException; nested PropertyAccessExceptions (1) are:
PropertyAccessException 1: org.springframework.beans.TypeMismatchException: Failed to convert property value of type [org.springframework.beans.factory.config.TypedStringValue] to required type [java.lang.Object] for property 'conversionRate'; nested exception is java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Double
Caused by: org.springframework.beans.PropertyBatchUpdateException; nested PropertyAccessException details (1) are:
PropertyAccessException 1:
org.springframework.beans.TypeMismatchException: Failed to convert property value of type [org.springframework.beans.factory.config.TypedStringValue] to required type [java.lang.Object] for property 'conversionRate'; nested exception is java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Double
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Double
	at com.mcparland.john.conversion.RateMultiplierConverter.setConversionRate(RateMultiplierConverter.java:1)
	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:597)
	at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:821)
	at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:645)
	at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:78)
	at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:59)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1127)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:862)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:423)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:249)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:155)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:246)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:160)
	at com.mcparland.john.conversion.ConverterApp.main(ConverterApp.java:36)

I cannot understand what the problem is in this case. Can anyone help?

Thanks,

John

[Lino Larios]

Hi

You can try something like this

<bean id="simple" ...> <property name="rate" ref="doubleValue"/> </bean> <bean id="doubleValue" class="java.lang.Double"> <constructor-arg index="0" value="1.609344"/> </bean>

Regards

[John McParland]

Thanks Lino, that worked!

What I don't quite understand now is why the second example required me to use;

<bean id="milesToKm" class="com.mcparland.john.conversion.RateMultiplierConverter"> <property name="conversionRate" ref="doubleRate"/> <property name="convertFromUnitName" value="UK Miles"/> <property name="convertToUnitName" value="Kilometres"/> </bean> <bean id="doubleRate" class="java.lang.Double"> <constructor-arg index="0" value="1.609344"/> </bean>

when the first example required just;

<bean id="simple" class="com.mcparland.john.conversion.Simple"> <property name="rate" value="1.609344"/> </bean>

The only real difference I can see between the class definitions is the first implements an interface with a generic type to use Double, the second uses the Double type explicitly.


Snippets of both classes;

public class Simple {

    private Double rate = 0.0d;
    
    public void setRate(Double rate) {
...

   public Double getRate() {
...

public class RateMultiplierConverter implements Converter<Double> {

    private Double conversionRate = 0.0d;

    @Override
    public Double getConversionRate() {
...
    @Override
    public void setConversionRate(Double rate) {