RestTemplate報錯：no suitable HttpMessageConverter found for request type

某天試用RestTemplate調試，瀏覽器直接提示：

This application has no explicit mapping for /error, so you are seeing this as a fallback.

Fri Dec 01 14:49:26 CST 2017

There was an unexpected error (type=Internal Server Error, status=500).

Could not write request: no suitable HttpMessageConverter found for request type [org.springframework.util.LinkedMultiValueMap] and content type [application/x-www-form-urlencoded;charset=UTF-8]

查看後臺是RestTemplate模板異常：

org.springframework.web.client.RestClientException: Could not write request: no suitable HttpMessageConverter found for request type [org.springframework.util.LinkedMultiValueMap] and content type [application/x-www-form-urlencoded;charset=UTF-8]

異常提示已經很明顯了，原因是由於我的post方法使用了MultiValueMap<String, Object>來封裝參數，但是無法找到合適的類型轉換，仔細查看我的RestTemplate對象獲取方式是如下的：

     public static RestTemplate getInstance(String charset) {
          StringHttpMessageConverter m = new StringHttpMessageConverter(Charset.forName(charset));
          RestTemplate restTemplate = new RestTemplateBuilder().additionalMessageConverters(m).build();
          return restTemplate;
     }

其實問題就出現在上面這段代碼上面，我使用了RestTemplateBuilder來創建RestTemplate對象，該方式只會爲restTemplate模板初始化一個HttpMessageConverter(注：StringHttpMessageConverter間接實現HttpMessageConverter接口)

再比較直接 new RestTemplate()創建對象的方式

找到原因所在，可以不使用RestTemplateBuilder創建對象來避免這個異常，爲此對getInstance方法改造成以下的形式:

    public static RestTemplate getInstanceByCharset(String charset) {
        RestTemplate restTemplate = new RestTemplate();
        restTemplate.getMessageConverters().add(new StringHttpMessageConverter(Charset.forName(charset)));
        return restTemplate;
    }

後臺不再報錯，問題完美解決！