321 lines
17 KiB
Plaintext
321 lines
17 KiB
Plaintext
[[java-rest-low-usage]]
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== Getting started
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This section describes how to get started with the low-level REST client from
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getting the artifact to using it in an application.
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[[java-rest-low-javadoc]]
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=== Javadoc
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The javadoc for the low level REST client can be found at {rest-client-javadoc}/index.html.
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[[java-rest-low-usage-maven]]
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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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The low-level REST client is subject to the same release cycle as
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elasticsearch. Replace the 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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[[java-rest-low-usage-maven-maven]]
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==== Maven configuration
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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>elasticsearch-rest-client</artifactId>
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<version>{version}</version>
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</dependency>
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--------------------------------------------------
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[[java-rest-low-usage-maven-gradle]]
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==== Gradle configuration
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Here is how you can configure the dependency using gradle as a dependency manager.
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Add the following to your `build.gradle` file:
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["source","groovy",subs="attributes"]
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--------------------------------------------------
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dependencies {
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compile 'org.elasticsearch.client:elasticsearch-rest-client:{version}'
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}
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--------------------------------------------------
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[[java-rest-low-usage-dependencies]]
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=== Dependencies
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The low-level Java REST client uses several https://www.apache.org/[Apache] libraries:
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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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One of the most important is the http://hc.apache.org/httpcomponents-asyncclient-dev/[Apache Http Async Client]
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which is used to send http requests. In order to avoid version conflicts, these dependencies are shaded and
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packaged within the client in a single JAR file (sometimes called "uber jar" or "fat jar"). Shading a dependency
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consists of taking its content (resources files and Java class files), rename its packages (all package names
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that start with `org.apache` are renamed to `org.elasticsearch.client`) before putting them in the same JAR file
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as the low-level Java REST client.
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[[java-rest-low-usage-initialization]]
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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",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-init]
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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",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-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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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-init-default-headers]
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--------------------------------------------------
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<1> Set the default headers that need to be sent with each request, to
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prevent having to specify them with each single request
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-init-max-retry-timeout]
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--------------------------------------------------
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<1> Set the timeout that should be honoured in case multiple attempts are made
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for the same request. The default value is 30 seconds, same as the default
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socket timeout. In case the socket timeout is customized, the maximum retry
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timeout should be adjusted accordingly
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-init-failure-listener]
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--------------------------------------------------
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<1> Set a listener that gets notified every time a node fails, in case actions
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need to be taken. Used internally when sniffing on failure is enabled.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-init-request-config-callback]
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--------------------------------------------------
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<1> Set a callback that allows to modify the default request configuration
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(e.g. request timeouts, authentication, or anything that the `org.elasticsearch.client.http.client.config.RequestConfig.Builder`
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allows to set). For more information, see the https://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache/http/client/config/RequestConfig.Builder.html[Apache documentation]
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-init-client-config-callback]
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--------------------------------------------------
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<1> Set a callback that allows to modify the http client configuration
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(e.g. encrypted communication over ssl, or anything that the `org.elasticsearch.client.http.impl.nio.client.HttpAsyncClientBuilder`
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allows to set). For more information, see the http://hc.apache.org/httpcomponents-asyncclient-dev/httpasyncclient/apidocs/org/apache/http/impl/nio/client/HttpAsyncClientBuilder.html[Apache documentation]
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[[java-rest-low-usage-requests]]
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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` or `performRequestAsync` method variants.
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The `performRequest` methods are synchronous and return the `Response` directly,
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meaning that the client will block and wait for a response to be returned.
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The `performRequestAsync` variants return `void` and accept an extra
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`ResponseListener` as an argument instead, meaning that they are executed
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asynchronously. The provided listener will be notified upon request completion
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or failure.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-verb-endpoint]
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--------------------------------------------------
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<1> Send a request by providing only the verb and the endpoint, minimum set
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of required arguments
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-verb-endpoint-params]
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--------------------------------------------------
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<1> Send a request by providing the verb, the endpoint, and some querystring
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parameter
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-verb-endpoint-params-body]
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--------------------------------------------------
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<1> Send a request by providing the verb, the endpoint, optional querystring
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parameters and the request body enclosed in an `org.elasticsearch.client.http.HttpEntity`
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object
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IMPORTANT: The `ContentType` specified for the `HttpEntity` is important
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because it will be used to set the `Content-Type` header so that Elasticsearch
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can properly parse the content.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-response-consumer]
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--------------------------------------------------
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<1> Send a request by providing the verb, the endpoint, optional querystring
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parameters, optional request body and the optional factory that is used to
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create a `org.elasticsearch.client.http.nio.protocol.HttpAsyncResponseConsumer` (see the http://hc.apache.org/httpcomponents-core-ga/httpcore-nio/apidocs/org/apache/http/nio/protocol/HttpAsyncResponseConsumer.html[Apache documentation])
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callback instance per request attempt. Controls how the response body gets
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streamed from a non-blocking HTTP connection on the client side. When not
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provided, the default implementation is used which buffers the whole response
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body in heap memory, up to 100 MB.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-verb-endpoint-async]
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--------------------------------------------------
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<1> Define what needs to happen when the request is successfully performed
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<2> Define what needs to happen when the request fails, meaning whenever
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there's a connection error or a response with error status code is returned.
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<3> Send an async request by providing only the verb, the endpoint, and the
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response listener to be notified once the request is completed, minimum set
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of required arguments
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-verb-endpoint-params-async]
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--------------------------------------------------
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<1> Send an async request by providing the verb, the endpoint, some querystring
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parameter and the response listener to be notified once the request is completed
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-verb-endpoint-params-body-async]
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--------------------------------------------------
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<1> Send an async request by providing the verb, the endpoint, optional
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querystring parameters, the request body enclosed in an
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`org.elasticsearch.client.http.HttpEntity` object and the response listener to be
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notified once the request is completed
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-response-consumer-async]
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--------------------------------------------------
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<1> Send an async request by providing the verb, the endpoint, optional
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querystring parameters, optional request body and the optional factory that is
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used to create a `org.elasticsearch.client.http.nio.protocol.HttpAsyncResponseConsumer` (see the http://hc.apache.org/httpcomponents-core-ga/httpcore-nio/apidocs/org/apache/http/nio/protocol/HttpAsyncResponseConsumer.html[Apache documentation])
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callback instance per request attempt. Controls how the response body gets
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streamed from a non-blocking HTTP connection on the client side. When not
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provided, the default implementation is used which buffers the whole response
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body in heap memory, up to 100 MB.
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The following is a basic example of how async requests can be sent:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-async-example]
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--------------------------------------------------
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<1> Process the returned response
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<2> Handle the returned exception, due to communication error or a response
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with status code that indicates an error
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Each of the above listed method supports sending headers along with the
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request through a `Header` varargs argument as in the following examples:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-headers]
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--------------------------------------------------
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-headers-async]
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--------------------------------------------------
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[[java-rest-low-usage-responses]]
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=== Reading responses
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The `Response` object, either returned by the synchronous `performRequest` methods or
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received as an argument in `ResponseListener#onSuccess(Response)`, wraps the
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response object returned by the http client and exposes some additional information.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/RestClientDocumentation.java[rest-client-response2]
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--------------------------------------------------
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<1> Information about the performed request
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<2> The host that returned the response
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<3> The response status line, from which you can for instance retrieve the status code
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<4> The response headers, which can also be retrieved by name though `getHeader(String)`
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<5> The response body enclosed in a `org.elasticsearch.client.http.HttpEntity` object
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(see the https://hc.apache.org/httpcomponents-core-ga/httpcore/apidocs/org/apache/http/HttpEntity.html[Apache documentation]
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When performing a request, an exception is thrown (or received as an argument
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in `ResponseListener#onFailure(Exception)` in the following scenarios:
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`IOException`:: communication problem (e.g. SocketTimeoutException)
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`ResponseException`:: a response was returned, but its status code indicated
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an error (not `2xx`). 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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NOTE: A `ResponseException` is **not** thrown for `HEAD` requests that return
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a `404` status code because it is an expected `HEAD` response that simply
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denotes that the resource is not found. All other HTTP methods (e.g., `GET`)
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throw a `ResponseException` for `404` responses unless the `ignore` parameter
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contains `404`. `ignore` is a special client parameter that doesn't get sent
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to Elasticsearch and contains a comma separated list of error status codes.
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It allows to control whether some error status code should be treated as an
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expected response rather than as an exception. This is useful for instance
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with the get api as it can return `404` when the document is missing, in which
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case the response body will not contain an error but rather the usual get api
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response, just without the document as it was not found.
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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 low-level Java Rest Client ships with different `org.elasticsearch.client.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 org.elasticsearch.client.http.nio.protocol.HttpAsyncResponseConsumer`
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that controls how bytes are read and buffered.
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[[java-rest-low-usage-logging]]
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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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