Spring MVC REST requestParam to handle multiple values for the same key

Question

I am making GET request and it has 2 parameters or basically an array

param {
paramNo:1,
from:mobile,
to:server
}
param {
paramNo:2,
from:server,
to:mobile
}

In my controller I have captured it as

public  @ResponseBody SearchResponse serverSearch(@RequestParam List<String> param) throws Exception {
     ObjectMapper mapper = new ObjectMapper();
     List<SearchInfo> searchInfo = mapper.readValue(param,new TypeReference<List<SearchInfo>>(){});
}

mapper.readValue does not take a List. It is throwing compilation error.

Question

1. I would prefer to retrieve it as (@RequestParam List param) rather than invoking objectMapper. What should I do convert it directly to List
2. how do I convert List to List?

Answer 1

You will have to use arrays instead of lists initially, but you can easily do a: List<SearchInfo> params = Arrays.asList(myArray);

Converting JSON

If your parameters are valid JSON, as it seems from your example, it's quite simple to convert into a custom object, see here.

---

Converting something else

Otherwise you can create a custom formatter with Spring that will format the Strings that come from your request parameters into your custom objects. Basically you'll have to first create a class that registers the type of objects to format and which class does the formatting:

import org.springframework.format.FormatterRegistrar;
import org.springframework.format.FormatterRegistry;

public class SearchInfoFormatterRegistrar implements FormatterRegistrar {
  @Override
  public void registerFormatters(FormatterRegistry registry) {
    registry.addFormatterForFieldType(SearchInfo.class, new SearchInfoFormatter());
  }
}

Then implement the class doing the formatting (mind you, this is not just casting an object to a different type, you actually have to use some logic):

import org.springframework.format.Formatter;

public class SearchInfoFormatter implements Formatter<SearchInfo> {
  @Override
  public String print(SearchInfo info, Locale locale) {
    // Format SearchInfo into String here.
  }

  @Override
  public SearchInfo parse(String text, Locale locale) {
    // Format String into SearchInfo here.
  }
}

Finally, you add them into your configuration:

<bean name="conversionService"
      class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
    <property name="formatterRegistrars">
        <set>
            <bean class="org.my.SearchInfoFormatterRegistrar" />
        </set>
    </property>
</bean>