Send JSON as parameter in url using RestTemplate

If you try to send the json as a parameter in url via Spring’s RestTemplate, you will encounter the following error:

HttpClientErrorException$BadRequest: 400 : [{"Message":"Wrong format. See specification description; Unexpected character ('%' (code 37)): expected a valid value (number, String, array, object, 'true', 'false' or 'null')\n at [Source: (String)\... (541 bytes)]

In order to solve this problem, you need to:

Encode the URL yourself
Disable url encoding at the RestTemplate level.

Let’s do that:

private String encodeUrl(String apiBaseUrl) throws Exception {
    URIBuilder b = new URIBuilder(apiBaseUrl);
    b.addParameter("jsonArg", "{\"field1\":\"value1\"}");
    b.addParameter("simpleArg", "value2");
    return b.build().toString();
}


RestTemplate restTemplate = new RestTemplate();
...
DefaultUriBuilderFactory defaultUriBuilderFactory = new DefaultUriBuilderFactory();
defaultUriBuilderFactory.setEncodingMode(DefaultUriBuilderFactory.EncodingMode.NONE);
restTemplate.setUriTemplateHandler(defaultUriBuilderFactory);

String url = encodeUrl("http://localhost:8080");
String response = restTemplate.getForObject(url, String.class);

Many thanks to Chris Liu for showing how to disable url encoding in RestTemplate: http://www.chrispad.com/2019/04/disable-encoding-url-using-resttemplate.html.

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