Get Alias API

The Get Alias API uses GetAliasesRequest as its request object. One or more aliases can be optionally provided either at construction time or later on through the relevant setter method.

GetAliasesRequest request = new GetAliasesRequest();
GetAliasesRequest requestWithAlias = new GetAliasesRequest("alias1");
GetAliasesRequest requestWithAliases =
        new GetAliasesRequest(new String[]{"alias1", "alias2"});

The following arguments can optionally be provided:

request.aliases("alias"); 

request.indices("index"); 

request.indicesOptions(IndicesOptions.lenientExpandOpen()); 

request.local(true); 

When executing a GetAliasesRequest in the following manner, the client waits for the GetAliasesResponse to be returned before continuing with code execution:

GetAliasesResponse response = client.indices().getAlias(request, RequestOptions.DEFAULT);

Synchronous calls may throw an IOException in case of either failing to parse the REST response in the high-level REST client, the request times out or similar cases where there is no response coming back from the server.

In cases where the server returns a 4xx or 5xx error code, the high-level client tries to parse the response body error details instead and then throws a generic ElasticsearchException and adds the original ResponseException as a suppressed exception to it.

Executing a GetAliasesRequest can also be done in an asynchronous fashion so that the client can return directly. Users need to specify how the response or potential failures will be handled by passing the request and a listener to the asynchronous get-alias method:

client.indices().getAliasAsync(request, RequestOptions.DEFAULT, listener); 

The asynchronous method does not block and returns immediately. Once it is completed the ActionListener is called back using the onResponse method if the execution successfully completed or using the onFailure method if it failed. Failure scenarios and expected exceptions are the same as in the synchronous execution case.

A typical listener for get-alias looks like:

ActionListener<GetAliasesResponse> listener =
        new ActionListener<GetAliasesResponse>() {
            @Override
            public void onResponse(GetAliasesResponse getAliasesResponse) {
                
            }

            @Override
            public void onFailure(Exception e) {
                
            }
};

The returned GetAliasesResponse allows to retrieve information about the executed operation as follows:

Map<String, Set<AliasMetadata>> aliases = response.getAliases(); 

GetAliasesResponse class contains information about errors if they occurred. This info could be in fields error or exception depends on a case.

RestStatus status = response.status(); 
ElasticsearchException exception = response.getException(); 
String error = response.getError(); 

If user specified indices or aliases as regular expressions and nothing was found client returns OK status and no errors.