StringHttpMessageConverter DEFAULT_CHARSET Limitation for Turkish Content

Spring has its own REST support known as Spring Web MVC. Although, I am happy with its general capabilities, I came up with a small but very annoying problem or, let’s say, a limitation related to one of its HttpMessageConverter classes.

Spring Web MVC makes use of HttpMessageConverter classes both on the server and client to handle HTTP requests and generate responses as well, and one of those converters is StringHttpMessageConverter. It is very easy to generate a String response via this converter and @ResponseBody annotation. For example;

@Controller
public class StringResponseBodyTestController {
    @RequestMapping(value="/hello")
    @ResponseBody
    public String hello() {
        return "hello world";
    }
}

StringHttpMessageConverter looks for the HTTP request’s Accept header and tries to extract the charset parameter out of it. If it can’t, then it uses the DEFAULT_CHARSET constant value, which is ISO-8859-1. Unfortunately, content that has some special Turkish characters won’t display correctly with the default charset.

public String hello() {
    return "hello world - ıİğĞşŞ";
}

It is easy to set the Accept header value if you are using a REST client utility, e.g., Spring’s RestTemplate.

RestTemplate template = new RestTemplate();

HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.set("Accept", "text/html;charset=utf-8");

HttpEntity<?> requestEntity =
new HttpEntity(requestHeaders);

HttpEntity response = template.exchange(
"http://localhost/hello", HttpMethod.GET,
requestEntity, String.class);

System.out.println(response.getBody());

However, if you are trying to access your REST services via a browser, then you will have a problem. Because adding TR among your preferred languages won’t help, as this causes the Accept-Language header to change only. As you see from the above example, we need to add the charset=utf-8 parameter to the Accept header. If you are using Firefox, the only possible way, as far as I know, is to use an add-on like Modify Headers or HeaderTool.

The bad thing about StringHttpMessageConverter is that it doesn’t provide any facility to change this behavior. Currently, there are several issues in the Spring JIRA system that ask for a fix or enhancement to this HttpMessageConverter.