= Using SolrJ
:solr-root-path: ../../
:example-source-dir: {solr-root-path}solrj/src/test/org/apache/solr/client/ref_guide_examples/
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{solr-javadocs}/solr-solrj/[SolrJ] is an API that makes it easy for applications written in Java (or any language based on the JVM) to talk to Solr. SolrJ hides a lot of the details of connecting to Solr and allows your application to interact with Solr with simple high-level methods.  SolrJ supports most Solr APIs, and is highly configurable.

== Building and Running SolrJ Applications

The SolrJ API ships with Solr, so you do not have to download or install anything else. But you will need to configure your build to include SolrJ and its dependencies.

=== Common Build Systems

Most mainstream build systems greatly simplify dependency management, making it easy to add SolrJ to your project.

For projects built with Ant (using http://ant.apache.org/ivy/[Ivy]), place the following in your `ivy.xml`:

[source,xml,subs="verbatim,attributes"]
----
<dependency org="org.apache.solr" name="solr-solrj" rev="{solr-docs-version}.0"/>
----

For projects built with Maven, place the following in your `pom.xml`:

[source,xml,subs="verbatim,attributes"]
----
<dependency>
  <groupId>org.apache.solr</groupId>
  <artifactId>solr-solrj</artifactId>
  <version>{solr-docs-version}.0</version>
</dependency>
----

For projects built with Gradle, place the following in your `build.gradle`:

[source,groovy,subs="attributes"]
----
compile group: 'org.apache.solr', name: 'solr-solrj', version: '{solr-docs-version}.0'
----

=== Adding SolrJ to the Classpath Manually

If you are not using one of the above build system, it's still easy to add SolrJ to your build.

At build time, all that is required is the SolrJ jar itself: `solr-solrj-{solr-docs-version}.0.jar`.  To compile code manually that uses SolrJ, use a `javac` command similar to:

[source,bash,subs="attributes"]
----
javac -cp .:$SOLR_HOME/dist/solr-solrj-{solr-docs-version}.0.jar ...
----

At runtime, you need a few of SolrJ's dependencies, in addition to SolrJ itself. For convenience, these dependencies are made available in the `dist/solrj-lib` directory.  Run your project with a classpath like:

[source,bash,subs="attributes"]
----
java -cp .:$SOLR_HOME/dist/solrj-lib/*:$SOLR_HOME/dist/solr-solrj-{solr-docs-version}.0.jar ...
----

If you are worried about the SolrJ libraries expanding the size of your client application, you can use a code obfuscator like http://proguard.sourceforge.net/[ProGuard] to remove APIs that you are not using.

== SolrJ Overview

For all its flexibility, SolrJ is built around a few simple interfaces.

All requests to Solr are sent by a {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/SolrClient.html[`SolrClient`].  SolrClient's are the main workhorses at the core of SolrJ.  They handle the work of connecting to and communicating with Solr, and are where most of the user configuration happens.

Requests are sent in the form of {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/SolrRequest.html[`SolrRequests`], and are returned as {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/SolrResponse.html[`SolrResponses`].

=== Types of SolrClients

`SolrClient` has a few concrete implementations, each geared towards a different usage-pattern or resiliency model:

- {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/impl/HttpSolrClient.html[`HttpSolrClient`] - geared towards query-centric workloads, though also a good general-purpose client.  Communicates directly with a single Solr node.
- {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/impl/Http2SolrClient.html[`Http2SolrClient`] - async, non-blocking and general-purpose client that leverage HTTP/2. This class is experimental therefore its API's might change or be removed in minor versions of SolrJ.
- {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/impl/LBHttpSolrClient.html[`LBHttpSolrClient`] - balances request load across a list of Solr nodes. Adjusts the list of "in-service" nodes based on node health.
- {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/impl/LBHttp2SolrClient.html[`LBHttp2SolrClient`] - just like `LBHttpSolrClient` but using `Http2SolrClient` instead. This class is experimental therefore its API's might change or be removed in minor versions of SolrJ.
- {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/impl/CloudSolrClient.html[`CloudSolrClient`] - geared towards communicating with SolrCloud deployments. Uses already-recorded ZooKeeper state to discover and route requests to healthy Solr nodes.
- {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/impl/ConcurrentUpdateSolrClient.html[`ConcurrentUpdateSolrClient`] - geared towards indexing-centric workloads.  Buffers documents internally before sending larger batches to Solr.
- {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj/impl/ConcurrentUpdateHttp2SolrClient.html[`ConcurrentUpdateSolrClient`] - just like `ConcurrentUpdateSolrClient` but using `Http2SolrClient` instead. This class is experimental therefore its API's might change or be removed in minor versions of SolrJ.

=== Common Configuration Options

Most SolrJ configuration happens at the `SolrClient` level.  The most common/important of these are discussed below.  For comprehensive information on how to tweak your `SolrClient`, see the Javadocs for the involved client, and its corresponding builder object.

==== Base URLs
Most `SolrClient` implementations (except for `CloudSolrClient` and `Http2SolrClient`) require users to specify one or more Solr base URLs, which the client then uses to send HTTP requests to Solr.  The path users include on the base URL they provide has an effect on the behavior of the created client from that point on.

. A URL with a path pointing to a specific core or collection (e.g., `\http://hostname:8983/solr/core1`).  When a core or collection is specified in the base URL, subsequent requests made with that client are not required to re-specify the affected collection.  However, the client is limited to sending requests to  that core/collection, and can not send requests to any others.
. A URL pointing to the root Solr path (e.g., `\http://hostname:8983/solr`).  When no core or collection is specified in the base URL, requests can be made to any core/collection, but the affected core/collection must be specified on all requests.

Generally speaking, if your `SolrClient` will only be used on a single core/collection, including that entity in the path is the most convenient.  Where more flexibility is required, the collection/core should be excluded.

==== Base URLs of Http2SolrClient
Since `Http2SolrClient` can manages connections to different nodes efficiently. `Http2SolrClient`
does not require a `baseUrl`. In case of `baseUrl` is not provided, `SolrRequest.basePath` must be set, so
`Http2SolrClient` can know which node it will request to. If not an `IllegalArgumentException` will be thrown.

==== Timeouts
All `SolrClient` implementations allow users to specify the connection and read timeouts for communicating with Solr.  These are provided at client creation time, as in the example below:

[source,java,indent=0]
----
include::{example-source-dir}UsingSolrJRefGuideExamplesTest.java[tag=solrj-solrclient-timeouts]
----

When these values are not explicitly provided, SolrJ falls back to using the defaults for the OS/environment is running on.

== Querying in SolrJ
`SolrClient` has a number of `query()` methods for fetching results from Solr.  Each of these methods takes in a `SolrParams`,an object encapsulating arbitrary query-parameters.  And each method outputs a `QueryResponse`, a wrapper which can be used to access the result documents and other related metadata.

The following snippet uses a SolrClient to query Solr's "techproducts" example collection, and iterate over the results.

[source,java,indent=0]
----
include::{example-source-dir}UsingSolrJRefGuideExamplesTest.java[tag=solrj-query-with-raw-solrparams]
----

`SolrParams` has a `SolrQuery` subclass, which provides some convenience methods that greatly simplifies query creation.  The following snippet shows how the query from the previous example can be built using some of the convenience methods in `SolrQuery`:

[source,java,indent=0]
----
include::{example-source-dir}UsingSolrJRefGuideExamplesTest.java[tag=solrj-query-with-solrquery]
----

== Indexing in SolrJ

Indexing is also simple using SolrJ.  Users build the documents they want to index as instances of `SolrInputDocument`, and provide them as arguments to one of the `add()` methods on `SolrClient`.

The following example shows how to use SolrJ to add a document to Solr's "techproducts" example collection:

[source,java,indent=0]
----
include::{example-source-dir}UsingSolrJRefGuideExamplesTest.java[tag=solrj-index-with-raw-solrinputdoc]
----

CAUTION: The indexing examples above are intended to show syntax.  For brevity, they break several Solr indexing best-practices.  Under normal circumstances, documents should be indexed in larger batches, instead of one at a time.  It is also suggested that Solr administrators commit documents using Solr's autocommit settings, and not using explicit `commit()` invocations.

== Java Object Binding
While the `UpdateResponse` and `QueryResponse` interfaces that SolrJ provides are useful, it is often more convenient to work with domain-specific objects that can more easily be understood by your application.  Thankfully, SolrJ supports this by implicitly converting documents to and from any class that has been specially marked with {solr-javadocs}/solr-solrj/org/apache/solr/client/solrj//beans/Field.html[`Field`] annotations.

Each instance variable in a Java object can be mapped to a corresponding Solr field, using the `Field` annotation.  The Solr field shares the name of the annotated variable by default, however, this can be overridden by providing the annotation with an explicit field name.

The example snippet below shows an annotated `TechProduct` class that can be used to represent results from Solr's "techproducts" example collection.

[source,java,indent=0]
----
include::{example-source-dir}UsingSolrJRefGuideExamplesTest.java[tag=solrj-techproduct-value-type]
----

Application code with access to the annotated `TechProduct` class above can index `TechProduct` objects directly without any conversion, as in the example snippet below:

[source,java,indent=0]
----
include::{example-source-dir}UsingSolrJRefGuideExamplesTest.java[tag=solrj-index-bean-value-type]
----

Similarly, search results can be converted directly into bean objects using the `getBeans()` method on `QueryResponse`:

[source,java,indent=0]
----
include::{example-source-dir}UsingSolrJRefGuideExamplesTest.java[tag=solrj-query-bean-value-type]
----

== Other APIs
SolrJ allows more than just querying and indexing.  It supports all of Solr's APIs.  Accessing Solr's other APIs is as easy as finding the appropriate request object, providing any necessary parameters, and passing it to the `request()` method of your `SolrClient`.  `request()` will return a `NamedList`: a generic object which mirrors the hierarchical structure of the JSON or XML returned by their request.

The example below shows how SolrJ users can call the CLUSTERSTATUS API of SolrCloud deployments, and manipulate the returned `NamedList`:

[source,java,indent=0]
----
include::{example-source-dir}UsingSolrJRefGuideExamplesTest.java[tag=solrj-other-apis]
----
