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<h2 class="title"><a id="java-input-plugin"></a>How to write a Java input plugin<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h2>
</div></div></div>
<div class="warning admon">
<div class="icon"></div>
<div class="admon_content">
<p>This functionality is in beta and is subject to change. The design and code is less mature than official GA features and is being provided as-is with no warranties. Beta features are not subject to the support SLA of official GA features.</p>
</div>
</div>
<p>To develop a new Java input for Logstash, you write a new Java class that
conforms to the Logstash Java Inputs API, package it, and install it with the
logstash-plugin utility. We’ll go through each of those steps.</p>
<h3><a id="_set_up_your_environment"></a>Set up your environment<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h3>
<h4><a id="_copy_the_example_repo"></a>Copy the example repo<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<p>Start by copying the <a href="https://github.com/logstash-plugins/logstash-input-java_input_example" class="ulink" target="_top">example input plugin</a>. The plugin API is currently part of the
Logstash codebase so you must have a local copy of that available. You can
obtain a copy of the Logstash codebase with the following <code class="literal">git</code> command:</p>
<div class="pre_wrapper lang-shell">
<pre class="programlisting prettyprint lang-shell">git clone --branch <branch_name> --single-branch https://github.com/elastic/logstash.git <target_folder></pre>
</div>
<p>The <code class="literal">branch_name</code> should correspond to the version of Logstash containing the
preferred revision of the Java plugin API.</p>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p>The beta version of the Java plugin API is available in the <code class="literal">6.7</code>
branch of the Logstash codebase.</p>
</div>
</div>
<p>Specify the <code class="literal">target_folder</code> for your local copy of the Logstash codebase. If you
do not specify <code class="literal">target_folder</code>, it defaults to a new folder called <code class="literal">logstash</code>
under your current folder.</p>
<h4><a id="_generate_the_jar_file"></a>Generate the .jar file<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<p>After you have obtained a copy of the appropriate revision of the Logstash
codebase, you need to compile it to generate the .jar file containing the Java
plugin API. From the root directory of your Logstash codebase ($LS_HOME), you
can compile it with <code class="literal">./gradlew assemble</code> (or <code class="literal">gradlew.bat assemble</code> if you’re
running on Windows). This should produce the
<code class="literal">$LS_HOME/logstash-core/build/libs/logstash-core-x.y.z.jar</code> where <code class="literal">x</code>, <code class="literal">y</code>, and
<code class="literal">z</code> refer to the version of Logstash.</p>
<p>After you have successfully compiled Logstash, you need to tell your Java plugin
where to find the <code class="literal">logstash-core-x.y.z.jar</code> file. Create a new file named
<code class="literal">gradle.properties</code> in the root folder of your plugin project. That file should
have a single line:</p>
<div class="pre_wrapper lang-txt">
<pre class="programlisting prettyprint lang-txt">LOGSTASH_CORE_PATH=<target_folder>/logstash-core</pre>
</div>
<p>where <code class="literal">target_folder</code> is the root folder of your local copy of the Logstash codebase.</p>
<h3><a id="_code_the_plugin"></a>Code the plugin<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h3>
<p>The example input plugin generates a configurable number of simple events before
terminating. Let’s look at the main class in the example input.</p>
<div class="pre_wrapper lang-java">
<pre class="programlisting prettyprint lang-java">@LogstashPlugin(name="java_input_example")
public class JavaInputExample implements Input {
public static final PluginConfigSpec<Long> EVENT_COUNT_CONFIG =
PluginConfigSpec.numSetting("count", 3);
public static final PluginConfigSpec<String> PREFIX_CONFIG =
PluginConfigSpec.stringSetting("prefix", "message");
private String id;
private long count;
private String prefix;
private final CountDownLatch done = new CountDownLatch(1);
private volatile boolean stopped;
public JavaInputExample(String id, Configuration config, Context context) {
this.id = id;
count = config.get(EVENT_COUNT_CONFIG);
prefix = config.get(PREFIX_CONFIG);
}
@Override
public void start(Consumer<Map<String, Object>> consumer) {
int eventCount = 0;
try {
while (!stopped && eventCount < count) {
eventCount++;
consumer.accept.push(Collections.singletonMap("message",
prefix + " " + StringUtils.center(eventCount + " of " + count, 20)));
}
} finally {
stopped = true;
done.countDown();
}
}
@Override
public void stop() {
stopped = true; // set flag to request cooperative stop of input
}
@Override
public void awaitStop() throws InterruptedException {
done.await(); // blocks until input has stopped
}
@Override
public Collection<PluginConfigSpec<?>> configSchema() {
return Arrays.asList(EVENT_COUNT_CONFIG, PREFIX_CONFIG);
}
@Override
public String getId() {
return this.id;
}
}</pre>
</div>
<p>Let’s step through and examine each part of that class.</p>
<h4><a id="_class_declaration_5"></a>Class declaration<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<div class="pre_wrapper lang-java">
<pre class="programlisting prettyprint lang-java">@LogstashPlugin(name="java_input_example")
public class JavaInputExample implements Input {</pre>
</div>
<p>Notes about the class declaration:</p>
<div class="ulist itemizedlist">
<ul class="itemizedlist">
<li class="listitem">
<p>All Java plugins must be annotated with the <code class="literal">@LogstashPlugin</code> annotation. Additionally:</p>
<div class="ulist itemizedlist">
<ul class="itemizedlist">
<li class="listitem">
The <code class="literal">name</code> property of the annotation must be supplied and defines the name of the plugin as it will be used
in the Logstash pipeline definition. For example, this input would be referenced in the input section of the
Logstash pipeline defintion as <code class="literal">input { java_input_example => { .... } }</code>
</li>
<li class="listitem">
The value of the <code class="literal">name</code> property must match the name of the class excluding casing and underscores.
</li>
</ul>
</div>
</li>
<li class="listitem">
The class must implement the <code class="literal">co.elastic.logstash.api.Input</code> interface.
</li>
</ul>
</div>
<h4><a id="_plugin_settings"></a>Plugin settings<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<p>The snippet below contains both the setting definition and the method referencing it.</p>
<div class="pre_wrapper lang-java">
<pre class="programlisting prettyprint lang-java">public static final PluginConfigSpec<Long> EVENT_COUNT_CONFIG =
PluginConfigSpec.numSetting("count", 3);
public static final PluginConfigSpec<String> PREFIX_CONFIG =
PluginConfigSpec.stringSetting("prefix", "message");
@Override
public Collection<PluginConfigSpec<?>> configSchema() {
return Arrays.asList(EVENT_COUNT_CONFIG, PREFIX_CONFIG);
}</pre>
</div>
<p>The <code class="literal">PluginConfigSpec</code> class allows developers to specify the settings that a
plugin supports complete with setting name, data type, deprecation status,
required status, and default value. In this example, the <code class="literal">count</code> setting defines
the number of events that will be generated and the <code class="literal">prefix</code> setting defines an
optional prefix to include in the event field. Neither setting is required and
if it is not explicitly set, the settings default to <code class="literal">3</code> and <code class="literal">message</code>,
respectively.</p>
<p>The <code class="literal">configSchema</code> method must return a list of all settings that the plugin
supports. In a future phase of the Java plugin project, the Logstash execution
engine will validate that all required settings are present and that no
unsupported settings are present.</p>
<h4><a id="_constructor_and_initialization"></a>Constructor and initialization<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<div class="pre_wrapper lang-java">
<pre class="programlisting prettyprint lang-java">private String id;
private long count;
private String prefix;
public JavaInputExample(String id, Configuration config, Context context) {
this.id = id;
count = config.get(EVENT_COUNT_CONFIG);
prefix = config.get(PREFIX_CONFIG);
}</pre>
</div>
<p>All Java input plugins must have a constructor taking a <code class="literal">String</code> id and
<code class="literal">Configuration</code> and <code class="literal">Context</code> argument. This is the constructor that will be
used to instantiate them at runtime. The retrieval and validation of all plugin
settings should occur in this constructor. In this example, the values of the
two plugin settings are retrieved and stored in local variables for later use in
the <code class="literal">start</code> method.</p>
<p>Any additional initialization may occur in the constructor as well. If there are
any unrecoverable errors encountered in the configuration or initialization of
the input plugin, a descriptive exception should be thrown. The exception will
be logged and will prevent Logstash from starting.</p>
<h4><a id="_start_method"></a>Start method<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<div class="pre_wrapper lang-java">
<pre class="programlisting prettyprint lang-java">@Override
public void start(Consumer<Map<String, Object>> consumer) {
int eventCount = 0;
try {
while (!stopped && eventCount < count) {
eventCount++;
consumer.accept.push(Collections.singletonMap("message",
prefix + " " + StringUtils.center(eventCount + " of " + count, 20)));
}
} finally {
stopped = true;
done.countDown();
}
}</pre>
</div>
<p>The <code class="literal">start</code> method begins the event-producing loop in an input. Inputs are flexible and may produce events through
many different mechanisms including:</p>
<div class="ulist itemizedlist">
<ul class="itemizedlist">
<li class="listitem">
a pull mechanism such as periodic queries of external database</li>
</li>
<li class="listitem">
a push mechanism such as events sent from clients to a local network port</li>
</li>
<li class="listitem">
a timed computation such as a heartbeat</li>
</li>
<li class="listitem">
any other mechanism that produces a useful stream of events. Event streams may be either finite or infinite.
If the input produces an infinite stream of events, this method should loop until a stop request is made through
the <code class="literal">stop</code> method. If the input produces a finite stream of events, this method should terminate when the last
event in the stream is produced or a stop request is made, whichever comes first.
</li>
</ul>
</div>
<p>Events should be constructed as instances of <code class="literal">Map<String, Object></code> and pushed into the event pipeline via the
<code class="literal">Consumer<Map<String, Object>>.accept()</code> method.</p>
<h4><a id="_stop_and_awaitstop_methods"></a>Stop and awaitStop methods<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<div class="pre_wrapper lang-java">
<pre class="programlisting prettyprint lang-java">private final CountDownLatch done = new CountDownLatch(1);
private volatile boolean stopped;
@Override
public void stop() {
stopped = true; // set flag to request cooperative stop of input
}
@Override
public void awaitStop() throws InterruptedException {
done.await(); // blocks until input has stopped
}</pre>
</div>
<p>The <code class="literal">stop</code> method notifies the input to stop producing events. The stop
mechanism may be implemented in any way that honors the API contract though a
<code class="literal">volatile boolean</code> flag works well for many use cases.</p>
<p>Inputs stop both asynchronously and cooperatively. Use the <code class="literal">awaitStop</code> method to
block until the input has completed the stop process. Note that this method
should <span class="strong strong"><strong>not</strong></span> signal the input to stop as the <code class="literal">stop</code> method does. The
awaitStop mechanism may be implemented in any way that honors the API contract
though a <code class="literal">CountDownLatch</code> works well for many use cases.</p>
<h4><a id="_getid_method"></a>getId method<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<div class="pre_wrapper lang-java">
<pre class="programlisting prettyprint lang-java">@Override
public String getId() {
return id;
}</pre>
</div>
<p>For input plugins, the <code class="literal">getId</code> method should always return the id that was provided to the plugin through its
constructor at instantiation time.</p>
<h4><a id="_unit_tests"></a>Unit tests<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<p>Lastly, but certainly not least importantly, unit tests are strongly encouraged.
The example input plugin includes an
<a href="https://github.com/logstash-plugins/logstash-input-java_input_example/blob/master/src/test/java/org/logstash/javaapi/JavaInputExampleTest.java" class="ulink" target="_top">example unit
test</a> that you can use as a template for your own.</p>
<h3><a id="_package_and_deploy"></a>Package and deploy<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h3>
<p>Java plugins are packaged as Ruby gems for dependency management and
interoperability with Ruby plugins.</p>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p>One of the goals for Java plugin support is to eliminate the need for any
knowledge of Ruby or its toolchain for Java plugin development. Future phases of
the Java plugin project will automate the packaging of Java plugins as Ruby gems
so no direct knowledge of or interaction with Ruby will be required. In the
current phase, Java plugins must still be manually packaged as Ruby gems
and installed with the <code class="literal">logstash-plugin</code> utility.</p>
</div>
</div>
<h4><a id="_compile_to_jar_file"></a>Compile to JAR file<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<p>The Java plugin should be compiled and assembled into a fat jar with the
<code class="literal">vendor</code> task in the Gradle build file. This will package all Java dependencies
into a single jar and write it to the correct folder for later packaging into a
Ruby gem.</p>
<h4><a id="_manually_package_as_ruby_gem"></a>Manually package as Ruby gem<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<p>Several Ruby source files are required to package the jar file as a
Ruby gem. These Ruby files are used only at Logstash startup time to identify
the Java plugin and are not used during runtime event processing.</p>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p>These Ruby source files will be automatically generated in a future release.</p>
</div>
</div>
<p><span class="strong strong"><strong><code class="literal">logstash-input-<input-name>.gemspec</code></strong></span></p>
<div class="pre_wrapper lang-txt">
<pre class="programlisting prettyprint lang-txt">Gem::Specification.new do |s|
s.name = 'logstash-input-java_input_example'
s.version = PLUGIN_VERSION
s.licenses = ['Apache-2.0']
s.summary = "Example input using Java plugin API"
s.description = ""
s.authors = ['Elasticsearch']
s.email = '[email protected]'
s.homepage = "http://www.elastic.co/guide/en/logstash/current/index.html"
s.require_paths = ['lib', 'vendor/jar-dependencies']
# Files
s.files = Dir["lib/**/*","spec/**/*","*.gemspec","*.md","CONTRIBUTORS","Gemfile","LICENSE","NOTICE.TXT", "vendor/jar-dependencies/**/*.jar", "vendor/jar-dependencies/**/*.rb", "VERSION", "docs/**/*"]
# Special flag to let us know this is actually a logstash plugin
s.metadata = { 'logstash_plugin' => 'true', 'logstash_group' => 'input'}
# Gem dependencies
s.add_runtime_dependency "logstash-core-plugin-api", ">= 1.60", "<= 2.99"
s.add_runtime_dependency 'jar-dependencies'
s.add_development_dependency 'logstash-devutils'
end</pre>
</div>
<p>You can use this file with the following modifications:</p>
<div class="ulist itemizedlist">
<ul class="itemizedlist">
<li class="listitem">
<code class="literal">s.name</code> must follow the <code class="literal">logstash-input-<input-name></code> pattern
</li>
<li class="listitem">
<code class="literal">s.version</code> must match the <code class="literal">project.version</code> specified in the <code class="literal">build.gradle</code> file.
Both versions should be set to be read from the <code class="literal">VERSION</code> file in this example.
</li>
</ul>
</div>
<p><span class="strong strong"><strong><code class="literal">lib/logstash/inputs/<input-name>.rb</code></strong></span></p>
<div class="pre_wrapper lang-ruby">
<pre class="programlisting prettyprint lang-ruby"># encoding: utf-8
require "logstash/inputs/base"
require "logstash/namespace"
require "logstash-input-java_input_example_jars"
require "java"
class LogStash::Inputs::JavaInputExample < LogStash::Inputs::Base
config_name "java_input_example"
def self.javaClass() org.logstash.javaapi.JavaInputExample.java_class; end
end</pre>
</div>
<p>Modify these items in the file above:</p>
<div class="ulist itemizedlist">
<ul class="itemizedlist">
<li class="listitem">
Change the name to correspond with the input name.
</li>
<li class="listitem">
Change <code class="literal">require "logstash-input-java_input_example_jars"</code> to reference the appropriate "jars" file
as described below.
</li>
<li class="listitem">
Change <code class="literal">class LogStash::Inputs::JavaInputExample < LogStash::Inputs::Base</code> to provide a unique and
descriptive Ruby class name.
</li>
<li class="listitem">
Change <code class="literal">config_name "java_input_example"</code> to match the name of the plugin as specified in the <code class="literal">name</code> property of
the <code class="literal">@LogstashPlugin</code> annotation.
</li>
<li class="listitem">
Change <code class="literal">def self.javaClass() org.logstash.javaapi.JavaInputExample.java_class; end</code> to return the
class of the Java input.
</li>
</ul>
</div>
<p><span class="strong strong"><strong><code class="literal">lib/logstash-input-<input-name>_jars.rb</code></strong></span></p>
<div class="pre_wrapper lang-txt">
<pre class="programlisting prettyprint lang-txt">require 'jar_dependencies'
require_jar('org.logstash.javaapi', 'logstash-input-java_input_example', '0.0.1')</pre>
</div>
<p>In the file above:</p>
<div class="ulist itemizedlist">
<ul class="itemizedlist">
<li class="listitem">
Rename the file to correspond to the input name.
</li>
<li class="listitem">
Change the <code class="literal">require_jar</code> directive to correspond to the <code class="literal">group</code> specified in the
Gradle build file, the name of the input JAR file, and the version as
specified in both the gemspec and Gradle build file.
</li>
</ul>
</div>
<p>After you have created the previous files and the plugin JAR file, build the gem using the
following command:</p>
<div class="pre_wrapper lang-shell">
<pre class="programlisting prettyprint lang-shell">gem build logstash-input-<input-name>.gemspec</pre>
</div>
<h4><a id="_installing_the_java_plugin_in_logstash"></a>Installing the Java plugin in Logstash<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h4>
<p>After you have packaged your Java plugin as a Ruby gem, you can install it in
Logstash with this command:</p>
<div class="pre_wrapper lang-shell">
<pre class="programlisting prettyprint lang-shell">bin/logstash-plugin install --no-verify --local /path/to/javaPlugin.gem</pre>
</div>
<p>For Windows platforms: Substitute backslashes for forward slashes as appropriate in the command.</p>
<h3><a id="_running_logstash_with_the_java_input_plugin"></a>Running Logstash with the Java input plugin<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h3>
<p>The following is a minimal Logstash configuration that can be used to test that
the Java input plugin is correctly installed and functioning.</p>
<div class="pre_wrapper lang-java">
<pre class="programlisting prettyprint lang-java">input {
java_input_example {}
}
output {
stdout { codec => rubydebug }
}</pre>
</div>
<p>Copy the above Logstash configuration to a file such as <code class="literal">java_input.conf</code>.
Start Logstash with:</p>
<div class="pre_wrapper lang-shell">
<pre class="programlisting prettyprint lang-shell">bin/logstash --java-execution -f /path/to/java_input.conf</pre>
</div>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p>The <code class="literal">--java-execution</code> flag to enable the Java execution engine is
required as Java plugins are not supported in the Ruby execution engine.</p>
</div>
</div>
<p>The expected Logstash output (excluding initialization) with the configuration above is:</p>
<div class="pre_wrapper lang-txt">
<pre class="programlisting prettyprint lang-txt">{
"@version" => "1",
"message" => "message 1 of 3 ",
"@timestamp" => yyyy-MM-ddThh:mm:ss.SSSZ
}
{
"@version" => "1",
"message" => "message 2 of 3 ",
"@timestamp" => yyyy-MM-ddThh:mm:ss.SSSZ
}
{
"@version" => "1",
"message" => "message 3 of 3 ",
"@timestamp" => yyyy-MM-ddThh:mm:ss.SSSZ
}</pre>
</div>
<h3><a id="_feedback"></a>Feedback<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/logstash/edit/6.8/docs/static/contributing-java-plugin.asciidoc">edit</a></h3>
<p>If you have any feedback on Java plugin support in Logstash, please comment on our
<a href="https://github.com/elastic/logstash/issues/9215" class="ulink" target="_top">main Github issue</a> or post in the
<a href="https://discuss.elastic.co/c/logstash" class="ulink" target="_top">Logstash forum</a>.</p>
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