Whitelabel Connection Timeout should instead be a handled Gateway Timeout

[kaladay]

When outside the internal network, my connection will (correctly) timeout.
A ConnectException is being thrown, which is not being handled by the existing @ControllerAdvice.

I think CatalogService is acting as a "gateway" to OKAPI/FOLIO/etc.., so this error response feels more appropriate to me than an internal server error.

I do not think the ConnectException should be directly handled in this case because a ConnectException is too broad and we need to specifically handle Gateway Timeouts and report them. (There may be a desire to also handle all ConnectException, so this could be two distinct changes).

I am suggesting that the code that is performing a edge/okapi requests to catch ConnectException and then construct and thrown a Gateway Exception that should already be handled by the existing HttpServerErrorException advice. This would allow us to provide a more specific message, namely "Gateway Timeout", and possibly reference the service, such as:
504: Gateway Timeout while connecting to OKAPI.

The whitelabel for ConnectException in any other situation could still be handling with custom controller advice, but this would not be a Gateway Timeout and could probably be just set to an Internal Exception, such as:

    @ExceptionHandler(ConnectException.class)
    public ResponseEntity<String> parseError(ConnectException e, WebRequest request) {
        logger.error(e.getMessage());

        if (logger.isDebugEnabled()) {
            e.printStackTrace();
        }

        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
            .contentType(MediaType.TEXT_PLAIN)
            .body(e.getMessage());
    }

[kaladay]

A snippet of the exception looks like:

2021-03-22 09:56:46.251 ERROR 19367 --- [nio-9000-exec-1] e.t.c.exception.RestExceptionHandler     : Connection timed out (Connection timed
java.net.ConnectException: Connection timed out (Connection timed out)
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
        at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
        at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
        at java.net.Socket.connect(Socket.java:607)
        at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:284)
        at sun.security.ssl.BaseSSLSocketImpl.connect(BaseSSLSocketImpl.java:173)
        at sun.net.NetworkClient.doConnect(NetworkClient.java:180)
        at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
        at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
        at sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:264)
        at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:367)
        at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:191)
        at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1162)
        at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1056)
        at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:177)
        at sun.net.www.protocol.https.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:167)
        at org.springframework.http.client.SimpleBufferingClientHttpRequest.executeInternal(SimpleBufferingClientHttpRequest.java:78)
        at org.springframework.http.client.AbstractBufferingClientHttpRequest.executeInternal(AbstractBufferingClientHttpRequest.java:48)
        at org.springframework.http.client.AbstractClientHttpRequest.execute(AbstractClientHttpRequest.java:53)
        at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:661)
        at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:622)
        at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:296)
        at edu.tamu.catalog.service.FolioCatalogService.getFeesFines(FolioCatalogService.java:137)
...