1.     HttpHeaders requestHeaders = new HttpHeaders();
        requestHeaders.add("key1", "values");
        requestHeaders.add("key2", "ddd");
2.     HttpEntity<String> requestEntity = new HttpEntity<String>(null, requestHeaders);
        ResponseEntity<String> response = template.exchange(url, HttpMethod.GET, requestEntity, String.class, params);

        String sttr = response.getBody();

第一步：定義HttpHeaders，然後設定header裡要帶的資訊；

第二步：把設定好的header放到HttpEntity<String>裡；

第三步：HttpEntity<String>放到exchange的引數裡；

第四步：getBody()取結果；