How to prevent parameter binding from interpreting commas in Spring 3.0.5?

I've tested your code: it's unbelievable, but I can't reproduce your issue. I've downloaded the latest version of spring (3.0.5), this is my controller:

package test;

import org.apache.commons.lang.StringUtils;
import org.apache.log4j.Logger;
import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
@RequestMapping("/test/**")
public class MyController {

    private static final Logger logger = Logger.getLogger(MyController.class);

    @RequestMapping(value = "/test/params", method = RequestMethod.GET)
    public void test(SearchRequestParams requestParams, BindingResult result) {
    logger.debug("fq = " + StringUtils.join(requestParams.getFq(), "|"));
    }
}

this is my SearchRequestParams class:

package test;

public class SearchRequestParams {
    private String[] fq;

    public String[] getFq() {
    return fq;
    }

    public void setFq(String[] fq) {
    this.fq = fq;
    }
}

and this is my simple spring configuration:

<bean id="urlMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" />

<bean class="test.MyController" />

<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix">
        <value>/WEB-INF/jsp/</value>
    </property>
    <property name="suffix">
        <value>.jsp</value>
    </property>
</bean>

I've tested my code within tomcat 7.0.8; when I type http://localhost:8080/testweb/test/params.htm?fq=foo,bar I'm able to read in my log file this line: DEBUG fq = foo,bar. What are the the differences from my code to yours? Am I doing something wrong? I'd like to help you, so if you have any doubts or if I can do some other tests for you, it will be a pleasure.

UPDATE / SOLUTION
With your code I've reproduced the issue; you have the tag <mvc:annotation-driven /> in your dispatcher servlet configuration, so you silently use a default conversion service, instance of FormattingConversionService, which contains a default converter from String to String[] that uses comma as separator. You have to use a different conversion service bean containing your own converter from String to String[]. You should use a different separator, I've choosed to use ";" because it's the separator commonly used into query string ("?first=1;second=2;third=3"):

import org.springframework.core.convert.converter.Converter;
import org.springframework.util.StringUtils;

public class CustomStringToArrayConverter implements Converter<String, String[]>{
   @Override
    public String[] convert(String source) {
        return StringUtils.delimitedListToStringArray(source, ";");
    }
}

Then you have to specify this conversion service bean in your configuration:

<mvc:annotation-driven conversion-service="conversionService" />

<bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <list>
            <bean class="au.org.ala.testspringbinding.CustomStringToArrayConverter" />
        </list>
    </property>
</bean>

The issue has fixed, now you should check for any side effects. I hope you don't need in your application the original conversion from String to String[] (with comma as separator). ;-)

I have found the most elegant and the shortest way for me - add @InitBinder to a @Controller:

@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(String[].class, new StringArrayPropertyEditor(null));
}

It will convert String to String[] without using separator (null param), with Spring class org.springframework.beans.propertyeditors.StringArrayPropertyEditor. If someone in same project will use new default conversion way, it will be ok.

As suggested by Philip Potter, I'm posting the "update" to my question as an answer, as it might've been easy to miss...

Down-grading from Spring 3.0.5.RELEASE to 3.0.4.RELEASE fixed the issue, when using the @RequestParam annotation, suggesting it is a bug with 3.0.5.

However, it does NOT fix the related issue, when binding to a form-backing bean - which is what I have in my webapp. I've tested all version back to 3.0.0.RELEASE and get the same result (/test?fq=foo,bar produces fq = foo|bar).

E.g.

@RequestMapping(value = "/test", method = RequestMethod.GET)
public void test(SearchRequestParams requestParams, BindingResult result) {
    logger.debug("fq = " + StringUtils.join(requestParams.getFq(), "|"));
}

where SearchRequestParams contains a field String[] fq.

If anyone has a fix for this, I'll gladly accept their answer.

javanna already pointed out the correct root cause. I just wanted to further point out that you can also remove the StringToArrayConverter altogether as shown here and here.