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异常信息

nested exception is org.springframework.web.client.RestClientException: Could not 
extract response: no suitable HttpMessageConverter found for response type [class 
java.util.Map] and content type [application/javascript;charset=utf-8]] with root cause

触发异常的代码

Map weatherMap = restTemplate.getForObject(url, Map.class);

分析原因

• 异常信息说的是：没给content-type是[application/javascript;charset=utf-8]的response找到合适的HttpMessageConverter
• 如果content-type=application/json就没问题
• 所以异常是application/javascript导致的，即：RestTemplate自带的HttpMessageConverters中没用能处理content-type=application/javascript的response的HttpMessageConverter

解决方法

Map weatherMap = restTemplate.getForObject(url, Map.class);

url是别人的接口，所以无法修改response的content-type，只能给restTemplate加一个能处理content-type=application/javascript的response的HttpMessageConverter

• RestTemplate默认自带了几个HttpMessageConverter（在RestTemplate的无参构造方法中）

	public RestTemplate() {
		this.messageConverters.add(new ByteArrayHttpMessageConverter());
		this.messageConverters.add(new StringHttpMessageConverter());
		this.messageConverters.add(new ResourceHttpMessageConverter(false));
		try {
			this.messageConverters.add(new SourceHttpMessageConverter<>());
		}
		catch (Error err) {
			// Ignore when no TransformerFactory implementation is available
		}
  	...
}

• 自定义能处理content-type=application/javascript的response的HttpMessageConverter

**
 * 解决：RestTemplate自带的HttpMessageConverters中没用能处理
 * content-type=application/javascript的response的HttpMessageConverter
 */
public class MyApplicationJavascriptHttpMessageConverter extends AbstractHttpMessageConverter {
    /**
     * restTemplate获得的响应的content-type满足下面的条件
     * 才会被该HttpMessageConverter处理
     */
    public MyApplicationJavascriptHttpMessageConverter() {
        // application/javascript
        super(new MediaType("application", "javascript", Charset.forName("UTF-8")));
    }

    /**
     * 检查传入的字节码是否符合要求
     *
     * @param clazz
     * @return 返回true才会执行readInternal()
     */
    @Override
    protected boolean supports(Class clazz) {
        return true;
    }

    /**
     * 将restTemplate获得的响应转化成clazz对应的类型
     *
     * @param clazz
     * @param inputMessage restTemplate获得的响应
     * @return
     */
    @Override
    protected Object readInternal(Class clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
        //restTemplate发送请求后获得的响应
        InputStream body = inputMessage.getBody();

        //将响应转成对应类型
        // 就是restTemplate.getForObject(url, Map.class)的返回值
        return JSON.parseObject(body, clazz);
    }

    /**
     * 还不知道该方法的功能
     * 该方法也不会被执行到
     *
     * @param o
     * @param outputMessage
     * @throws IOException
     * @throws HttpMessageNotWritableException
     */
    @Override
    protected void writeInternal(Object o, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
        //do nothing
        System.out.println("do nothing");
    }
}

• 将自定义的HttpMessageConverter加到restTemplate的HttpMessageConverters中

    @Bean
    public RestTemplate restTemplate() {
        RestTemplate restTemplate = new RestTemplate();

        //处理content-type=application/javascript的HttpMessageConverter
        restTemplate.getMessageConverters().add(new MyApplicationJavascriptHttpMessageConverter());

        return restTemplate;
    }