342 lines
15 KiB
Plaintext
342 lines
15 KiB
Plaintext
[[java-rest-high-search]]
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=== Search API
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[[java-rest-high-document-search-request]]
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==== Search Request
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The `SearchRequest` is used for any operation that has to do with searching
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documents, aggregations, suggestions and also offers ways of requesting
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highlighting on the resulting documents.
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In its most basic form, we can add a query to the request:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-basic]
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--------------------------------------------------
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<1> Creates the `SeachRequest`. Without arguments this runs against all indices.
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<2> Most search parameters are added to the `SearchSourceBuilder`. It offers setters for everything that goes into the search request body.
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<3> Add a `match_all` query to the `SearchSourceBuilder`.
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===== Optional arguments
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Let's first look at some of the optional arguments of a `SearchRequest`:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-indices-types]
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--------------------------------------------------
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<1> Restricts the request to an index
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<2> Limits the request to a type
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There are a couple of other interesting optional parameters:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-routing]
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--------------------------------------------------
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<1> Set a routing parameter
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-indicesOptions]
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--------------------------------------------------
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<1> Setting `IndicesOptions` controls how unavailable indices are resolved and
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how wildcard expressions are expanded
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-preference]
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--------------------------------------------------
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<1> Use the preference parameter e.g. to execute the search to prefer local
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shards. The default is to randomize across shards.
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===== Using the SearchSourceBuilder
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Most options controlling the search behavior can be set on the
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`SearchSourceBuilder`,
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which contains more or less the equivalent of the options in the search request
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body of the Rest API.
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Here are a few examples of some common options:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-source-basics]
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--------------------------------------------------
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<1> Create a `SearchSourceBuilder` with default options.
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<2> Set the query. Can be any type of `QueryBuilder`
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<3> Set the `from` option that determines the result index to start searching
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from. Defaults to 0.
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<4> Set the `size` option that determines the number of search hits to return.
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Defaults to 10.
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<5> Set an optional timeout that controls how long the search is allowed to
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take.
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After this, the `SearchSourceBuilder` only needs to be added to the
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`SearchRequest`:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-source-setter]
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--------------------------------------------------
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===== Specifying Sorting
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The `SearchSourceBuilder` allows to add one or more `SortBuilder` instances. There are four special implementations (Field-, Score-, GeoDistance- and ScriptSortBuilder).
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-source-sorting]
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--------------------------------------------------
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<1> Sort descending by `_score` (the default)
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<2> Also sort ascending by `_id` field
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===== Source filtering
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By default, search requests return the contents of the document `_source` but like in the Rest API you can overwrite this behavior. For example, you can turn off `_source` retrieval completely:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-source-filtering-off]
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--------------------------------------------------
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The method also accepts an array of one or more wildcard patterns to control which fields get included or excluded in a more fine grained way:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-source-filtering-includes]
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--------------------------------------------------
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[[java-rest-high-request-highlighting]]
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===== Requesting Highlighting
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Highlighting search results can be achieved by setting a `HighlightBuilder` on the
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`SearchSourceBuilder`. Different highlighting behaviour can be defined for each
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fields by adding one or more `HighlightBuilder.Field` instances to a `HighlightBuilder`.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-highlighting]
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--------------------------------------------------
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<1> Creates a new `HighlightBuilder`
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<2> Create a field highlighter for the `title` field
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<3> Set the field highlighter type
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<4> Add the field highlighter to the highlight builder
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There are many options which are explained in detail in the Rest API documentation. The Rest
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API parameters (e.g. `pre_tags`) are usually changed by
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setters with a similar name (e.g. `#preTags(String ...)`).
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Highlighted text fragments can <<java-rest-high-retrieve-highlighting,later be retrieved>> from the `SearchResponse`.
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===== Requesting Aggregations
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Aggregations can be added to the search by first creating the appropriate
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`AggregationBuilder` and then setting it on the `SearchSourceBuilder`. In the
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following example we create a `terms` aggregation on company names with a
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sub-aggregation on the average age of employees in the company:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations]
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--------------------------------------------------
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We will later see how to <<java-rest-high-retrieve-aggs,access aggregations>> in the `SearchResponse`.
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===== Requesting Suggestions
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To add Suggestions to the search request, use one of the `SuggestionBuilder` implementations
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that are easily accessible from the `SuggestBuilders` factory class. Suggestion builders
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need to be added to the top level `SuggestBuilder`, which itself can be set on the `SearchSourceBuilder`.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-suggestion]
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--------------------------------------------------
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<1> Creates a new `TermSuggestionBuilder` for the `user` field and
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the text `kmichy`
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<2> Adds the suggestion builder and names it `suggest_user`
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We will later see how to <<java-rest-high-retrieve-suggestions,retrieve suggestions>> from the
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`SearchResponse`.
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[[java-rest-high-document-search-sync]]
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==== Synchronous Execution
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When executing a `SearchRequest` in the following manner, the client waits
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for the `SearchResponse` to be returned before continuing with code execution:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-execute]
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--------------------------------------------------
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[[java-rest-high-document-search-async]]
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==== Asynchronous Execution
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Executing a `SearchRequest` can also be done in an asynchronous fashion so that
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the client can return directly. Users need to specify how the response or
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potential failures will be handled by passing in appropriate listeners:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-execute-async]
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--------------------------------------------------
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<1> Called when the execution is successfully completed.
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<2> Called when the whole `SearchRequest` fails.
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==== SearchResponse
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The `SearchResponse` that is returned by executing the search provides details
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about the search execution itself as well as access to the documents returned.
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First, there is useful information about the request execution itself, like the
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HTTP status code, execution time or wether the request terminated early or timed
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out:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-response-1]
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--------------------------------------------------
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Second, the response also provides information about the execution on the
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shard level by offering statistics about the total number of shards that were
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affected by the search, and the successful vs. unsuccessful shards. Possible
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failures can also be handled by iterating over an array off
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`ShardSearchFailures` like in the following example:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-response-2]
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--------------------------------------------------
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[[java-rest-high-retrieve-searchHits]]
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===== Retrieving SearchHits
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To get access to the returned documents, we need to first get the `SearchHits`
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contained in the response:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-get]
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--------------------------------------------------
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The `SearchHits` provides global information about all hits, like total number
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of hits or the maximum score:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-info]
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--------------------------------------------------
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Nested inside the `SearchHits` are the individual search results that can
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be iterated over:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-singleHit]
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--------------------------------------------------
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The `SearchHit` provides access to basic information like index, type, docId and
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score of each search hit:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-singleHit-properties]
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--------------------------------------------------
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Furthermore, it lets you get back the document source, either as a simple
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JSON-String or as a map of key/value pairs. In this map, regular fields
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are keyed by the field name and contain the field value. Multi-valued fields are
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returned as lists of objects, nested objects as another key/value map. These
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cases need to be cast accordingly:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-singleHit-source]
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--------------------------------------------------
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[[java-rest-high-retrieve-highlighting]]
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===== Retrieving Highlighting
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If <<java-rest-high-request-highlighting,requested>>, highlighted text fragments can be retrieved from each `SearchHit` in the result. The hit object offers
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access to a map of field names to `HighlightField` instances, each of which contains one
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or many highlighted text fragments:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-highlighting-get]
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--------------------------------------------------
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<1> Get the highlighting for the `title` field
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<2> Get one or many fragments containing the highlighted field content
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[[java-rest-high-retrieve-aggs]]
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===== Retrieving Aggregations
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Aggregations can be retrieved from the `SearchResponse` by first getting the
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root of the aggregation tree, the `Aggregations` object, and then getting the
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aggregation by name.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-get]
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--------------------------------------------------
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<1> Get the `by_company` terms aggregation
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<2> Get the buckets that is keyed with `Elastic`
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<3> Get the `average_age` sub-aggregation from that bucket
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Note that if you access aggregations by name, you need to specify the
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aggregation interface according to the type of aggregation you requested,
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otherwise a `ClassCastException` will be thrown:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-get-wrongCast]
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--------------------------------------------------
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<1> This will throw an exception because "by_company" is a `terms` aggregation
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but we try to retrieve it as a `range` aggregation
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It is also possible to access all aggregations as a map that is keyed by the
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aggregation name. In this case, the cast to the proper aggregation interface
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needs to happen explicitly:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-asMap]
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--------------------------------------------------
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There are also getters that return all top level aggregations as a list:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-asList]
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--------------------------------------------------
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And last but not least you can iterate over all aggregations and then e.g.
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decide how to further process them based on their type:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-iterator]
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--------------------------------------------------
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[[java-rest-high-retrieve-suggestions]]
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===== Retrieving Suggestions
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To get back the suggestions from a `SearchResponse`, use the `Suggest` object as an entry point and then retrieve the nested suggestion objects:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-suggestion-get]
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--------------------------------------------------
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<1> Use the `Suggest` class to access suggestions
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<2> Suggestions can be retrieved by name. You need to assign them to the correct
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type of Suggestion class (here `TermSuggestion`), otherwise a `ClassCastException` is thrown
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<3> Iterate over the suggestion entries
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<4> Iterate over the options in one entry
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