---
title: Initializing the Elasticsearch Java REST client
description: A RestClient instance can be built through the corresponding RestClientBuilder class, created via RestClient#builder(HttpHost...) static method. The only...
url: https://www.elastic.co/docs/reference/elasticsearch/clients/java/transport/rest-client/usage/initialization
products:
  - Elasticsearch
  - Elasticsearch Client
  - Elasticsearch Java Client
---

# Initializing the Elasticsearch Java REST client
<note>
  This is the legacy RestClient. Please migrate to [Rest5Client](https://www.elastic.co/docs/reference/elasticsearch/clients/java/transport/rest5-client), a drop-in replacement with an up-to-date http library.
</note>

A `RestClient` instance can be built through the corresponding `RestClientBuilder` class, created via `RestClient#builder(HttpHost...)` static method. The only required argument is one or more hosts that the client will communicate with, provided as instances of [HttpHost](https://hc.apache.org/httpcomponents-core-4.4.x/current/httpcore/apidocs/org/apache/http/HttpHost.html) as follows:
```java
RestClient restClient = RestClient.builder(
    new HttpHost("localhost", 9200, "http"),
    new HttpHost("localhost", 9201, "http")).build();
```

The `RestClient` class is thread-safe and ideally has the same lifecycle as the application that uses it. It is important that it gets closed when no longer needed so that all the resources used by it get properly released, as well as the underlying http client instance and its threads:
```java
restClient.close();
```

`RestClientBuilder` also allows to optionally set the following configuration parameters while building the `RestClient` instance:
```java
RestClientBuilder builder = RestClient.builder(
    new HttpHost("localhost", 9200, "http"));
Header[] defaultHeaders = new Header[]{new BasicHeader("header", "value")};
builder.setDefaultHeaders(defaultHeaders); 
```

```java
RestClientBuilder builder = RestClient.builder(
        new HttpHost("localhost", 9200, "http"));
builder.setFailureListener(new RestClient.FailureListener() {
    @Override
    public void onFailure(Node node) {
        <1>
    }
});
```

1. Set a listener that gets notified every time a node fails,  in case actions need to be taken. Used internally when sniffing on failure is enabled.

```java
RestClientBuilder builder = RestClient.builder(
    new HttpHost("localhost", 9200, "http"));
builder.setNodeSelector(NodeSelector.SKIP_DEDICATED_MASTERS); 
```

```java
RestClientBuilder builder = RestClient.builder(
        new HttpHost("localhost", 9200, "http"));
builder.setRequestConfigCallback(
    new RestClientBuilder.RequestConfigCallback() {
        @Override
        public RequestConfig.Builder customizeRequestConfig(
                RequestConfig.Builder requestConfigBuilder) {
            return requestConfigBuilder.setSocketTimeout(10000); 
        }
    });
```

```java
RestClientBuilder builder = RestClient.builder(
    new HttpHost("localhost", 9200, "http"));
builder.setHttpClientConfigCallback(new HttpClientConfigCallback() {
        @Override
        public HttpAsyncClientBuilder customizeHttpClient(
                HttpAsyncClientBuilder httpClientBuilder) {
            return httpClientBuilder.setProxy(
                new HttpHost("proxy", 9000, "http"));  
        }
    });
```