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[DOCS] add java REST client docs Add some docs on how to get started with the Java REST client, some common configuration that may be needed and the sniffer component.
228 lines
10 KiB
Plaintext
228 lines
10 KiB
Plaintext
== Getting started
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=== Maven Repository
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The low-level Java REST client is hosted on
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http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22org.elasticsearch.client%22[Maven
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Central]. The minimum Java version required is `1.7`.
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Here is how you can configure the dependency using maven as a dependency manager.
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Add the following to your `pom.xml` file:
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["source","xml",subs="attributes"]
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--------------------------------------------------
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<dependency>
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<groupId>org.elasticsearch.client</groupId>
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<artifactId>rest</artifactId>
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<version>{version}</version>
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</dependency>
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--------------------------------------------------
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The low-level REST client is subject to the same release cycle as
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elasticsearch. Replace `${es.version}` with the desired client version, first
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released with `5.0.0-alpha4`. There is no relation between the client version
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and the elasticsearch version that the client can communicate with. The
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low-level REST client is compatible with all elasticsearch versions.
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=== Dependencies
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The low-level Java REST client internally uses the
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http://hc.apache.org/httpcomponents-asyncclient-dev/[Apache Http Async Client]
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to send http requests. It depends on the following artifacts, namely the async
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http client and its own transitive dependencies:
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- org.apache.httpcomponents:httpasyncclient
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- org.apache.httpcomponents:httpcore-nio
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- org.apache.httpcomponents:httpclient
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- org.apache.httpcomponents:httpcore
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- commons-codec:commons-codec
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- commons-logging:commons-logging
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=== Initialization
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A `RestClient` instance can be built through the corresponding
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`RestClientBuilder` class, created via `RestClient#builder(HttpHost...)`
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static method. The only required argument is one or more hosts that the
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client will communicate with, provided as instances of
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https://hc.apache.org/httpcomponents-core-ga/httpcore/apidocs/org/apache/http/HttpHost.html[HttpHost]
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as follows:
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[source,java]
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--------------------------------------------------
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RestClient restClient = RestClient.builder(
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new HttpHost("http", "localhost", 9200),
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new HttpHost("http", "localhost", 9201)).build();
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--------------------------------------------------
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The `RestClient` class is thread-safe and ideally has the same lifecycle as
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the application that uses it. It is important that it gets closed when no
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longer needed so that all the resources used by it get properly released,
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as well as the underlying http client instance and its threads:
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[source,java]
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--------------------------------------------------
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restClient.close();
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--------------------------------------------------
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`RestClientBuilder` also allows to optionally set the following configuration
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parameters while building the `RestClient` instance:
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`setDefaultHeaders`:: default headers that need to be sent with each request,
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to prevent having to specify them with each single request
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`setMaxRetryTimeoutMillis`:: the timeout that should be honoured in case
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multiple attempts are made for the same request. The default value is 10
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seconds, same as the default socket timeout. In case the socket timeout is
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customized, the maximum retry timeout should be adjusted accordingly
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`setFailureListener`:: a listener that gets notified every time a node
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fails, in case actions need to be taken. Used internally when sniffing on
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failure is enabled
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`setRequestConfigCallback`:: callback that allows to modify the default
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request configuration (e.g. request timeouts, authentication, or anything that
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the https://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache/http/client/config/RequestConfig.Builder.html[`org.apache.http.client.config.RequestConfig.Builder`]
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allows to set)
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`setHttpClientConfigCallback`:: callback that allows to modify the http client
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configuration (e.g. encrypted communication over ssl, or anything that the
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http://hc.apache.org/httpcomponents-asyncclient-dev/httpasyncclient/apidocs/org/apache/http/impl/nio/client/HttpAsyncClientBuilder.html[`org.apache.http.impl.nio.client.HttpAsyncClientBuilder`]
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allows to set)
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=== Performing requests
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Once the `RestClient` has been created, requests can be sent by calling one of
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the available `performRequest` method variants. The ones that return the
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`Response` are executed synchronously, meaning that the client will block and
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wait for a response to be returned. The `performRequest` variants that return
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`void` accept a `ResponseListener` as an argument and are executed
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asynchronously. The provided listener will be notified upon completion or
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failure. The following are the arguments accepted by the different
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`performRequest` methods:
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`method`:: the http method or verb
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`endpoint`:: the request path, which identifies the Elasticsearch api to
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call (e.g. `/_cluster/health`)
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`params`:: the optional parameters to be sent as querystring parameters
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`entity`:: the optional request body enclosed in an
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`org.apache.http.HttpEntity` object
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`responseConsumer`:: the optional
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http://hc.apache.org/httpcomponents-core-ga/httpcore-nio/apidocs/org/apache/http/nio/protocol/HttpAsyncResponseConsumer.html[`org.apache.http.nio.protocol.HttpAsyncResponseConsumer`]
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callback. Controls how the response body gets streamed from a non-blocking
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HTTP connection on the client side. When not provided, the default
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implementation is used which buffers the whole response body in heap memory
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`responseListener`:: the listener to be notified upon request success or failure
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whenever the async `performRequest` method variants are used
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`headers`:: optional request headers
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=== Reading responses
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The `Response` object, either returned by the sync `performRequest` methods or
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received as an argument in `ResponseListener#onSucces(Response)`, wraps the
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response object returned by the http client and exposes the following information:
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`getRequestLine`:: information about the performed request
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`getHost`:: the host that returned the response
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`getStatusLine`:: the response status line
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`getHeaders`:: the response headers, which can also be retrieved by name
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though `getHeader(String)`
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`getEntity`:: the response body enclosed in an
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https://hc.apache.org/httpcomponents-core-ga/httpcore/apidocs/org/apache/http/HttpEntity.html[`org.apache.http.HttpEntity`]
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object
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When performing a request, an exception is thrown (or received as an argument
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in `ResponseListener#onSucces(Exception)` in the following scenarios:
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`IOException`:: communication problem (e.g. SocketTimeoutException etc.)
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`ResponseException`:: a response was returned, but its status code indicated
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an error (either `4xx` or `5xx`). A `ResponseException` originates from a valid
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http response, hence it exposes its corresponding `Response` object which gives
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access to the returned response.
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=== Example requests
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Here are a couple of examples:
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[source,java]
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--------------------------------------------------
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Response response = restClient.performRequest("GET", "/",
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Collections.singletonMap("pretty", "true"));
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System.out.println(EntityUtils.toString(response.getEntity()));
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//index a document
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HttpEntity entity = new NStringEntity(
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"{\n" +
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" \"user\" : \"kimchy\",\n" +
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" \"post_date\" : \"2009-11-15T14:12:12\",\n" +
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" \"message\" : \"trying out Elasticsearch\"\n" +
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"}", ContentType.APPLICATION_JSON);
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Response indexResponse = restClient.performRequest(
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"PUT",
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"/twitter/tweet/1",
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Collections.<String, String>emptyMap(),
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entity);
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--------------------------------------------------
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Note that the low-level client doesn't expose any helper for json marshalling
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and un-marshalling. Users are free to use the library that they prefer for that
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purpose.
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The underlying Apache Async Http Client ships with different
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https://hc.apache.org/httpcomponents-core-ga/httpcore/apidocs/org/apache/http/HttpEntity.html[`org.apache.http.HttpEntity`]
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implementations that allow to provide the request body in different formats
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(stream, byte array, string etc.). As for reading the response body, the
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`HttpEntity#getContent` method comes handy which returns an `InputStream`
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reading from the previously buffered response body. As an alternative, it is
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possible to provide a custom
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http://hc.apache.org/httpcomponents-core-ga/httpcore-nio/apidocs/org/apache/http/nio/protocol/HttpAsyncResponseConsumer.html[`org.apache.http.nio.protocol.HttpAsyncResponseConsumer`]
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that controls how bytes are read and buffered.
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The following is a basic example of how async requests can be sent:
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[source,java]
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--------------------------------------------------
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int numRequests = 10;
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final CountDownLatch latch = new CountDownLatch(numRequests);
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for (int i = 0; i < numRequests; i++) {
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restClient.performRequest(
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"PUT",
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"/twitter/tweet/" + i,
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Collections.<String, String>emptyMap(),
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//assume that the documents are stored in an entities array
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entities[i],
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new ResponseListener() {
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@Override
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public void onSuccess(Response response) {
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System.out.println(response);
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latch.countDown();
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}
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@Override
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public void onFailure(Exception exception) {
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latch.countDown();
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}
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}
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);
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}
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//wait for all requests to be completed
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latch.await();
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--------------------------------------------------
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=== Logging
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The Java REST client uses the same logging library that the Apache Async Http
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Client uses: https://commons.apache.org/proper/commons-logging/[Apache Commons Logging],
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which comes with support for a number of popular logging implementations. The
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java packages to enable logging for are `org.elasticsearch.client` for the
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client itself and `org.elasticsearch.client.sniffer` for the sniffer.
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The request tracer logging can also be enabled to log every request and
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corresponding response in curl format. That comes handy when debugging, for
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instance in case a request needs to be manually executed to check whether it
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still yields the same response as it did. Enable trace logging for the `tracer`
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package to have such log lines printed out. Do note that this type of logging is
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expensive and should not be enabled at all times in production environments,
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but rather temporarily used only when needed.
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