Java code to search haystack with a large amount of substrings efficiently

NeedleTree.java

import java.util.HashMap;
import java.util.Map;

class NeedleTree{
	private int codePoint;
	private boolean selfSet = false;
	private Map<Integer, NeedleTree> children = new HashMap<>();
	
	public NeedleTree(int codePoint){
		this.codePoint = codePoint;
	}
	
	public NeedleTree childOrNull(int codePoint){
		return children.get(codePoint);
	}
	
	public NeedleTree child(int codePoint){
		NeedleTree child = children.get(codePoint);
		if(child == null){
			children.put(codePoint, child = new NeedleTree(codePoint));
		}
		return child;
	}

	public boolean isSelfSet(){
		return selfSet;
	}

	public void markSelfSet(){
		selfSet = true;
	}
}

StringSearcher.java

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.HashMap;

class StringSearcher{
	private NeedleTree needles = new NeedleTree(-1);
	private boolean caseSensitive;
	private List<Integer> lengths = new ArrayList<>();
	private int maxLength;

	public StringSearcher(List<String> inputs, boolean caseSensitive){
		this.caseSensitive = caseSensitive;
		for(String input : inputs){
			if(!lengths.contains(input.length())){
				lengths.add(input.length());
			}
			NeedleTree tree = needles;
			for(int i = 0; i < input.length(); i++){
				tree = tree.child(caseSensitive ? input.codePointAt(i) : Character.toLowerCase(input.codePointAt(i)));
			}
			tree.markSelfSet();
		}
		maxLength = Collections.max(lengths);
	}

	public boolean matches(String haystack){
		if(!caseSensitive){
			haystack = haystack.toLowerCase();
		}
		for(int i = 0; i < haystack.length(); i++){
			String substring = haystack.substring(i, Math.min(i + maxLength, haystack.length())); // maybe we can even skip this and use from haystack directly?
			NeedleTree tree = needles;
			for(int j = 0; j < substring.length(); j++){
				tree = tree.childOrNull(substring.codePointAt(j));
				if(tree == null){
					break;
				}
				if(tree.isSelfSet()){
					return true;
				}
			}
		}
		return false;
	}
}