How to generate a logstash event within a custom java filter plugin after timeout?

I want to correlate messages sending to logstash within a filter and send them to the next filter of logstash inside the pipeline.

However I have successfully setup a custom logstash filter plugin according to elastic documentation.

My code of the filter plugin looks like this:

package org.logstashplugins;

import co.elastic.logstash.api.Configuration;
import co.elastic.logstash.api.Context;
import co.elastic.logstash.api.Event;
import co.elastic.logstash.api.Filter;
import co.elastic.logstash.api.FilterMatchListener;
import co.elastic.logstash.api.LogstashPlugin;
import co.elastic.logstash.api.PluginConfigSpec;
import org.apache.commons.lang3.StringUtils;

import java.util.Collection;
import java.util.Collections;
import java.util.*;

// class name must match plugin name
@LogstashPlugin(name = "java_filter_example")
public class JavaFilterExample implements Filter {

    public static final PluginConfigSpec<String> SOURCE_CONFIG =
            PluginConfigSpec.stringSetting("source", "message");

    private String id;
    private String sourceField;
    private List<String> buffer;
    

    public JavaFilterExample(String id, Configuration config, Context context)
    {
        // constructors should validate configuration options
        this.id = id;
        this.sourceField = config.get(SOURCE_CONFIG);
        this.buffer = new ArrayList<String>();
    }

    @Override
    public Collection<Event> filter(Collection<Event> events, FilterMatchListener matchListener)
    {
        for (Event e : events)
        {
            Object f = e.getField(sourceField);
            if (f instanceof String)
            {
                buffer.add((String) f);
                matchListener.filterMatched(e);
            }
        }
        return events;
    }

    @Override
    public Collection<PluginConfigSpec<?>> configSchema()
    {
        // should return a list of all configuration options for this plugin
        return Collections.singletonList(SOURCE_CONFIG);
    }

    @Override
    public String getId() 
    {
        return this.id;
    }
}

Now I want to add a Thread which is being executed in the background which runs over the buffer containing the messages and sends a correlated event after a timeout occurs or if a new event arrives containing a "finish" message.

My question is now, how can I trigger a new event and send it to the next filters in the logstash pipeline? What is the java API or class to this?

I know there is an Aggregate Filter Plugin which meet partially my requirements, but I have to implement different parsers for the messages so it is better to implement a custom plugin by my own. But it is not clear accoding to documentations how to send a new event without returning an collection of modified events inside the filter method. Can you help me to achieve this?

I need something like this (in pseudo code):

public void anotherFunctionInsideAnotherJavaClass(...)
{
    Logstash.sendEvent(new Event(...));
}

I need to generate and send an event inside an other context than inside the filter method. Is this possible to do?

Hopefully it is clear what my problem is.

Thanks.