RestTemplate在連接失敗的時候，會直接拋出異常，我們可以通過設(shè)置

restTemplate.setErrorHandler(new CustomErrorHandler());

來處理異常。但是這種靈活度不夠，不能在業(yè)務(wù)發(fā)生點靈活處理。

還有一種思路就是捕獲各種情況下的異常，之后根據(jù)異常類型就知道對應(yīng)的異常了。
HttpClientErrorException - 在HTTP狀態(tài)為4xx的情況下
HttpServerErrorException - 在HTTP狀態(tài)為5xx的情況下
UnknownHttpStatusCodeException - 如果HTTP狀態(tài)未知
ResourceAccessException - 請求超時，Spring將拋出該實例下的底層異常將是java.net.SocketTimeoutException。

代碼實現(xiàn)

        @Autowired
    private RestTemplate restTemplate;

    @RequestMapping("/netTest")
    public String netTest() {
        try {
            //String url = "http://127.0.0.1:8080/statusCode3xx";
            //String url = "http://127.0.0.1:8080/statusCode4xx";
            //String url = "http://127.0.0.1:8080/statusCode5xx";
            String url = "http://127.0.0.1:8080/timeout";
            String result = restTemplate.getForObject(url, String.class);
            logger.info(" result = " + result);
        } catch (HttpClientErrorException e) {// 4xx
            logger.error(" HttpClientErrorException , e = " + e.getMessage());
            e.printStackTrace();
        } catch (HttpServerErrorException e) {// 5xx
            logger.error(" HttpServerErrorException , e = " + e.getMessage());
            e.printStackTrace();
        } catch (UnknownHttpStatusCodeException e) {
            logger.error(" UnknownHttpStatusCodeException , e = " + e.getMessage());
            e.printStackTrace();
        }catch(HttpStatusCodeException  e){
            logger.error(" HttpStatusCodeException , e = " + e.getMessage());
            e.printStackTrace();
        }catch(ResourceAccessException e){//timeout
            logger.error(" ResourceAccessException , e = " + e.getMessage());
            e.printStackTrace();
        }
        return "netOK";
    }

    @RequestMapping("/statusCode3xx")
    public ResponseEntity<String> returnStatusCode3XX() {
        return new ResponseEntity<String>(" error ", HttpStatus.USE_PROXY);
    }
    
    @RequestMapping("/statusCode4xx")
    public ResponseEntity<String> returnStatusCode4XX() {
        return new ResponseEntity<String>(" error ", HttpStatus.UNAUTHORIZED);
    }

    @RequestMapping("/statusCode5xx")
    public ResponseEntity<String> returnStatusCode5XX() {
        return new ResponseEntity<String>(" error ", HttpStatus.SERVICE_UNAVAILABLE);
    }

    @RequestMapping("/timeout")
    public String returnTimeout() {
        try {
            Thread.sleep(9*1000L);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return " ok ";
    }