How to prevent parameter binding from interpreting

Question

Consider the following controller method:

@RequestMapping(value = "/test", method = RequestMethod.GET)
public void test(@RequestParam(value = "fq", required = false) String[] filterQuery) {
    logger.debug(fq = " + StringUtils.join(filterQuery, "|"));
}

Here is the output for different fq combinations:

1. /test?fq=foo results in fq = foo
2. /test?fq=foo&fq=bar results in fq = foo|bar
3. /test?fq=foo,bar results in fq = foo|bar
4. /test?fq=foo,bar&fq=bash results in fq = foo,bar|bash
5. /test?fq=foo,bar&fq= results in fq = foo,bar|

Example 3 is the problem. I expect (want/need) it to output fq = foo,bar.

I've tried escaping the comma with \ and using %3C but niether work.

If I look at the HttpServletRequest object's version:

String[] fqs = request.getParameterValues("fq");
logger.debug(fqs = " + StringUtils.join(fqs, "|"));

It prints the expected output: fqs = foo,bar. So the "problem" is with the Spring data binding.

I could by-pass Spring's binding and use HttpServletRequest but I really don't want to as I'm using a backing bean in my real code (same thing is happening) and don't wish to re-implement the binding functionality. I'm hoping someone can provide a simple way of preventing this behavior via escaping or some other mechanism.

TIA

UPDATE: I posted this Q on Twitter and got a reply saying the expected output appears with Spring 3.0.4.RELEASE. I've now confirmed this is the case and thus is a temporary fix. I'll go ahead and log this as a bug on the Spring JIRA system. If anyone can provide a work around or fix with 3.0.5, I'll accept their answer.

Answer 1

Its a hack but, have you considered passing your params delimited with '-'

/test?fq=foo-bar results in fq = foo-bar
/test?fq=foo-bar&fq=bash results in fq = foo-bar|bash 

Or any other delimiter maybe ~, or !,or ^, or ???

Answer 2

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.

Answer 3

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). ;-)

Answer 4

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.

Answer 5

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.