RestTemplate 是在使用 Spring Boot 開發傳案時一個非常好用的 HTTP 的工具。以往我們使用 JAVA 發送 HTTP 請求時總免不了要建立大量程式碼。但是使用 RestTemplate 則方便許多，程式碼也更為精簡。

例如以下以使用 HttpURLConnection 作為範例，發送 JSON 格式的請求，並將回傳資訊封裝為自訂議的 ResponseObject ：

     public void httpDemo() throws JsonProcessingException {
        String url = "http://demo.com/demo";
        RequestObject requestObject = new RequestObject();
        requestObject.setName("XXX");
        requestObject.setPhoneNo("0987654321");
        requestObject.setEmail("Demo@demo.demo");
        ObjectMapper objectMapper = new ObjectMapper();
        String requestData = objectMapper.writeValueAsString(requestObject);
        try {
            String responseData = demoHttpURLConnection(url, requestData);
            ResponseObject responseObject = objectMapper.readValue(responseData, ResponseObject.class);
            log.info(responseObject.toString());
        } catch (Exception e) {
            // TODO: handle exception
    public String demoHttpURLConnection(String url, String requestData) throws IOException {
        URL endpoint = new URL(url);
        HttpURLConnection httpUrlConn = (HttpURLConnection) endpoint.openConnection();
        httpUrlConn.setRequestMethod("POST");
        httpUrlConn.setRequestProperty("Content-Type", "application/json");
        OutputStream outputStream = httpUrlConn.getOutputStream();
        byte[] input = requestData.getBytes("utf-8");
        outputStream.write(input, 0, input.length);
        int statusCode = httpUrlConn.getResponseCode();
        InputStream inputStream = null;
        if (statusCode == 200) {
            inputStream = httpUrlConn.getInputStream();
        } else {
            inputStream = httpUrlConn.getErrorStream();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, "utf-8"));
        StringBuilder response = new StringBuilder();
        String responseLine = null;
        while ((responseLine = bufferedReader.readLine()) != null) {
            response.append(responseLine.trim());
        return response.toString();
 以上程式碼包含request、 response的JSON轉換以及發送http的流程。接著示範使用 RestTemplate。 
 
    public ResponseObject demoRestTemplate(String url, RequestObject requestObject) {
        RestTemplate restTemplate = new RestTemplate();
        ResponseObject responseObject = restTemplate.postForObject(url, requestObject, ResponseObject.class);
        return responseObject;
使用postForObject送與回傳都是已經用class封裝好的格式，流程變得更加精簡。除了post之外，也有get、put、patch、patch、delete等等各種方法。或是使用exchange可以填入自己要用的HttpMethod。且可在HttpEntity添加請求標頭。
 
    public ResponseObject demoRestTemplate2(String url, RequestObject requestObject) {
        RestTemplate restTemplate = new RestTemplate();
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.add("token", "NlXEt66fejIrQvIGampcPnLVdmIYVo0wdZf8T5H");
        HttpEntity<RequestObject> httpEntity = new HttpEntity<RequestObject>(requestObject, headers);
        ResponseEntity<ResponseObject> responseEntity = 
                restTemplate.exchange(url, HttpMethod.POST, httpEntity, ResponseObject.class);
        ResponseObject responseObject = responseEntity.getBody();
        return responseObject;
        使用uri變量：
 
    public User getUser(String id) {
        RestTemplate restTemplate = new RestTemplate();
        User user = restTemplate.getForObject("http://demo/user/{id}", User.class, id);
        return user;
如果有多個變量：
 
    public User getUser(String id, String name) {
        RestTemplate restTemplate = new RestTemplate();
        Map<String, String> uriVariables = new HashMap<String, String>();
        uriVariables.put("id", id);
        uriVariables.put("name", name);
        User user = restTemplate.getForObject("http://demo/user/{id}/{name}", User.class, uriVariables);
        return user;
           設定timeout：
 
    private SimpleClientHttpRequestFactory getClientHttpRequestFactory() {
        SimpleClientHttpRequestFactory clientHttpRequestFactory = new SimpleClientHttpRequestFactory();
        clientHttpRequestFactory.setConnectTimeout(1000);// 1秒
        return clientHttpRequestFactory;
    private RestTemplate restTemplate = new RestTemplate(getClientHttpRequestFactory());
 
        以上就是RestTemplate的一些簡單的使用方式，終於再也不用為了發HTTP請求而傷腦筋了！