== Common configuration The `RestClientBuilder` supports providing both a `RequestConfigCallback` and an `HttpClientConfigCallback` which allow for any customization that the Apache Async Http Client exposes. Those callbacks make it possible to modify some specific behaviour of the client without overriding every other default configuration that the `RestClient` is initialized with. This section describes some common scenarios that require additional configuration for the low-level Java REST Client. === Timeouts Configuring requests timeouts can be done by providing an instance of `RequestConfigCallback` while building the `RestClient` through its builder. The interface has one method that receives an instance of https://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache/http/client/config/RequestConfig.Builder.html[`org.apache.http.client.config.RequestConfig.Builder`] as an argument and has the same return type. The request config builder can be modified and then returned. In the following example we increase the connect timeout (defaults to 1 second) and the socket timeout (defaults to 30 seconds). Also we adjust the max retry timeout accordingly (defaults to 30 seconds too). [source,java] -------------------------------------------------- RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200)) .setRequestConfigCallback(new RestClientBuilder.RequestConfigCallback() { @Override public RequestConfig.Builder customizeRequestConfig(RequestConfig.Builder requestConfigBuilder) { return requestConfigBuilder.setConnectTimeout(5000) .setSocketTimeout(60000); } }) .setMaxRetryTimeoutMillis(60000) .build(); -------------------------------------------------- === Number of threads The Apache Http Async Client starts by default one dispatcher thread, and a number of worker threads used by the connection manager, as many as the number of locally detected processors (depending on what `Runtime.getRuntime().availableProcessors()` returns). The number of threads can be modified as follows: [source,java] -------------------------------------------------- RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200)) .setHttpClientConfigCallback(new RestClientBuilder.HttpClientConfigCallback() { @Override public HttpAsyncClientBuilder customizeHttpClient(HttpAsyncClientBuilder httpClientBuilder) { return httpClientBuilder.setDefaultIOReactorConfig( IOReactorConfig.custom().setIoThreadCount(1).build()); } }) .build(); -------------------------------------------------- === Basic authentication Configuring basic authentication can be done by providing an `HttpClientConfigCallback` while building the `RestClient` through its builder. The interface has one method that receives an instance of https://hc.apache.org/httpcomponents-asyncclient-dev/httpasyncclient/apidocs/org/apache/http/impl/nio/client/HttpAsyncClientBuilder.html[`org.apache.http.impl.nio.client.HttpAsyncClientBuilder`] as an argument and has the same return type. The http client builder can be modified and then returned. In the following example we set a default credentials provider that requires basic authentication. [source,java] -------------------------------------------------- final CredentialsProvider credentialsProvider = new BasicCredentialsProvider(); credentialsProvider.setCredentials(AuthScope.ANY, new UsernamePasswordCredentials("user", "password")); RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200)) .setHttpClientConfigCallback(new RestClientBuilder.HttpClientConfigCallback() { @Override public HttpAsyncClientBuilder customizeHttpClient(HttpAsyncClientBuilder httpClientBuilder) { return httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider); } }) .build(); -------------------------------------------------- === Encrypted communication Encrypted communication can also be configured through the `HttpClientConfigCallback`. The https://hc.apache.org/httpcomponents-asyncclient-dev/httpasyncclient/apidocs/org/apache/http/impl/nio/client/HttpAsyncClientBuilder.html[`org.apache.http.impl.nio.client.HttpAsyncClientBuilder`] received as an argument exposes multiple methods to configure encrypted communication: `setSSLContext`, `setSSLSessionStrategy` and `setConnectionManager`, in order of precedence from the least important. The following is an example: [source,java] -------------------------------------------------- KeyStore keyStore = KeyStore.getInstance("jks"); try (InputStream is = Files.newInputStream(keyStorePath)) { keyStore.load(is, keyStorePass.toCharArray()); } RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200)) .setHttpClientConfigCallback(new RestClientBuilder.HttpClientConfigCallback() { @Override public HttpAsyncClientBuilder customizeHttpClient(HttpAsyncClientBuilder httpClientBuilder) { return httpClientBuilder.setSSLContext(sslcontext); } }) .build(); -------------------------------------------------- === Others For any other required configuration needed, the Apache HttpAsyncClient docs should be consulted: https://hc.apache.org/httpcomponents-asyncclient-4.1.x/ .