OpenSearch/docs/java-rest/high-level/document/multi-get.asciidoc

[[java-rest-high-document-multi-get]]
=== Multi-Get API

The `multiGet` API executes multiple <<java-rest-high-document-get,`get`>>
requests in a single http request in parallel.

[[java-rest-high-document-mulit-get-request]]
==== Multi-Get Request

A `MultiGetRequest` is built empty and you add `MultiGetRequest.Item`s to
configure what to fetch:

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-request]
--------------------------------------------------
<1> Index
<2> Type
<3> Document id
<4> Add another item to fetch

==== Optional arguments

`multiGet` supports the same optional arguments that the
<<java-rest-high-document-get-request-optional-arguments,`get` API>> supports.
You can set most of these on the `Item`:

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-request-no-source]
--------------------------------------------------
<1> Disable source retrieval, enabled by default

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-request-source-include]
--------------------------------------------------
<1> Configure source inclusion for specific fields

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-request-source-exclude]
--------------------------------------------------
<1> Configure source exclusion for specific fields

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-request-stored]
--------------------------------------------------
<1> Configure retrieval for specific stored fields (requires fields to be
stored separately in the mappings)
<2> Retrieve the `foo` stored field (requires the field to be stored
separately in the mappings)

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-request-item-extras]
--------------------------------------------------
<1> Routing value
<2> Parent value
<3> Version
<4> Version type

{ref}/search-request-preference.html[`preference`],
{ref}/docs-get.html#realtime[`realtime`]
and
{ref}/docs-get.html#get-refresh[`refresh`] can be set on the main request but
not on any items:

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-request-top-level-extras]
--------------------------------------------------
<1> Preference value
<2> Set realtime flag to `false` (`true` by default)
<3> Perform a refresh before retrieving the document (`false` by default)

[[java-rest-high-document-multi-get-sync]]
==== Synchronous Execution

After building the `MultiGetRequest` you can execute it synchronously with
`multiGet`:

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-execute]
--------------------------------------------------

[[java-rest-high-document-multi-get-async]]
==== Asynchronous Execution

The asynchronous execution of a multi get request requires both the
`MultiGetRequest` instance and an `ActionListener` instance to be passed to
the asynchronous method:

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-execute-async]
--------------------------------------------------
<1> The `MultiGetRequest` to execute and the `ActionListener` to use when
the execution completes.

The asynchronous method does not block and returns immediately. Once the
request completed the `ActionListener` is called back using the `onResponse`
method if the execution successfully completed or using the `onFailure` method
if it failed.

A typical listener for `MultiGetResponse` looks like:

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-execute-listener]
--------------------------------------------------
<1> Called when the execution is successfully completed. The response is
provided as an argument.
<2> Called in case of failure. The raised exception is provided as an argument.

[[java-rest-high-document-multi-get-response]]
==== Multi Get Response

The returned `MultiGetResponse` contains a list of `MultiGetItemResponse`s in
`getResponses` in the same order that they were requested.
`MultiGetItemResponse` contains *either* a
<<java-rest-high-document-get-response, `GetResponse`>> if the get succeeded
or a `MultiGetResponse.Failure` if it failed. A success looks just like a
normal `GetResponse`.

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-response]
--------------------------------------------------
<1> `getFailure` returns null because there isn't a failure.
<2> `getResponse` returns the `GetResponse`.
<3> Retrieve the document as a `String`
<4> Retrieve the document as a `Map<String, Object>`
<5> Retrieve the document as a `byte[]`
<6> Handle the scenario where the document was not found. Note that although
the returned response has `404` status code, a valid `GetResponse` is
returned rather than an exception thrown. Such response does not hold any
source document and its `isExists` method returns `false`.

When one of the subrequests as performed against an index that does not exist
`getFailure` will contain an exception:

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-indexnotfound]
--------------------------------------------------
<1> `getResponse` is null.
<2> `getFailure` isn't and contains an `Exception`.
<3> That `Exception` is actually an `ElasticsearchException`
<4> and it has a status of `NOT_FOUND`. It'd have been an HTTP 404 if this
wasn't a multi get.
<5> `getMessage` explains the actual cause, `no such index`.

In case a specific document version has been requested, and the existing
document has a different version number, a version conflict is raised:

["source","java",subs="attributes,callouts,macros"]
--------------------------------------------------
include-tagged::{doc-tests}/CRUDDocumentationIT.java[multi-get-conflict]
--------------------------------------------------
<1> `getResponse` is null.
<2> `getFailure` isn't and contains an `Exception`.
<3> That `Exception` is actuall and `ElasticsearchException`
<4> and it has a status of `CONFLICT`. It'd have been an HTTP 409 if this
wasn't a multi get.
<5> `getMessage` explains the actual cause, `