JavaBeans 比较

Does anyone know about a free open source library (utility class) which allows you to compare two instances of one Java bean and return a list/array of properties which values are different in those two instances? Please post a small sample.

Cheers
Tomas

解决方案

BeanComparator of Apache commons is what you are looking for.

Update. A simple example that compares JavaBeans with one property (comparation is made agains only one property, you should create as many BeanComparators as properties you want to match).

import org.apache.commons.beanutils.BeanComparator;

public class TestBeanComparator
{
    public TestBeanComparator()
    {
    }

    public class TestBean
    {
        int value;

        public TestBean()
        {
        }

        public int getValue()
        {
            return value;
        }

        public void setValue(int value)
        {
            this.value = value;
        }
    }

    public static void main(String[] args)
    {
        TestBeanComparator tbc = new TestBeanComparator();

        tbc.go();
    }

    public void go()
    {
        TestBean tbs [] = new TestBean[10];

        for (int i = 0; i < tbs.length; i++)
        {
            tbs[i] = new TestBeanComparator.TestBean();
            tbs[i].setValue((int) (Math.random() * 10));

            System.out.println("TestBean["+i+"] = " + tbs[i].getValue());
        }

        BeanComparator bc = new BeanComparator("value");

        System.out.println("");
        System.out.println("Value to match: " + tbs[0].getValue());
        for (int i = 1; i < tbs.length; i++)
        {
            if(bc.compare(tbs[i], tbs[0]) == 0)
            {
               System.out.println("Match found in bean "+ i); 
            }
        }
    }
}

After some tests one result is successful. This is the output:

TestBean[0] = 0
TestBean[1] = 4
TestBean[2] = 0
TestBean[3] = 2
TestBean[4] = 7
TestBean[5] = 3
TestBean[6] = 0
TestBean[7] = 3
TestBean[8] = 7
TestBean[9] = 3

Value to match: 0
Match found in bean 2
Match found in bean 6

Obviously increasing TestBean array size will increase the chances to get matches.

You need to import to your project the following jars: commons-logging-version.jar, commons-beanutils-version.jar, commons-beanutils-core-version.jar, commons-beanutils-bean-collections-version.jar, commons-collections-version.jar.

The files are included inside commons-logging, commons-beanutils and commons-collections APIs.