Jackson is "the Java JSON library" or "the best JSON parser for Java". Or simply as "JSON for Java".

Jackson Databind Source Code files are provided in the source packge (jackson-databind-2.14.0-sources.jar). You can download it at Jackson Maven Website.

You can also browse Jackson Databind Source Code below:

⏎ com/fasterxml/jackson/databind/introspect/AnnotationMap.java

package com.fasterxml.jackson.databind.introspect;

import java.lang.annotation.Annotation;
import java.util.*;

import com.fasterxml.jackson.databind.util.Annotations;

/**
 * Simple helper class used to keep track of collection of
 * Jackson Annotations associated with annotatable things
 * (methods, constructors, classes).
 * Note that only Jackson-owned annotations are tracked (for now?).
 */
public final class AnnotationMap implements Annotations
{
    protected HashMap<Class<?>,Annotation> _annotations;

    public AnnotationMap() { }

    public static AnnotationMap of(Class<?> type, Annotation value) {
        HashMap<Class<?>,Annotation> ann = new HashMap<>(4);
        ann.put(type, value);
        return new AnnotationMap(ann);
    }

    AnnotationMap(HashMap<Class<?>,Annotation> a) {
        _annotations = a;
    }

    /*
    /**********************************************************
    /* Annotations impl
    /**********************************************************
     */
    
    @SuppressWarnings("unchecked")
    @Override
    public <A extends Annotation> A get(Class<A> cls)
    {
        if (_annotations == null) {
            return null;
        }
        return (A) _annotations.get(cls);
    }

    @Override
    public boolean has(Class<?> cls)
    {
        if (_annotations == null) {
            return false;
        }
        return _annotations.containsKey(cls);
    }

    /**
     * Helper method that can be used for a "bulk" check to see if at least
     * one of given annotation types is included within this map.
     *
     * @since 2.7
     */
    @Override
    public boolean hasOneOf(Class<? extends Annotation>[] annoClasses) {
        if (_annotations != null) {
            for (int i = 0, end = annoClasses.length; i < end; ++i) {
                if (_annotations.containsKey(annoClasses[i])) {
                    return true;
                }
            }
        }
        return false;
    }

    /*
    /**********************************************************
    /* Other API
    /**********************************************************
     */
    
    /**
     * @since 2.3
     */
    public Iterable<Annotation> annotations() {
        if (_annotations == null || _annotations.size() == 0) {
            return Collections.emptyList();
        }
        return _annotations.values();
    }
    
    public static AnnotationMap merge(AnnotationMap primary, AnnotationMap secondary)
    {
        if (primary == null || primary._annotations == null || primary._annotations.isEmpty()) {
            return secondary;
        }
        if (secondary == null || secondary._annotations == null || secondary._annotations.isEmpty()) {
            return primary;
        }
        HashMap<Class<?>,Annotation> annotations = new HashMap<Class<?>,Annotation>();
        // add secondary ones first
        for (Annotation ann : secondary._annotations.values()) {
            annotations.put(ann.annotationType(), ann);
        }
        // to be overridden by primary ones
        for (Annotation ann : primary._annotations.values()) {
            annotations.put(ann.annotationType(), ann);
        }
        return new AnnotationMap(annotations);
    }
    
    @Override
    public int size() {
        return (_annotations == null) ? 0 : _annotations.size();
    }

    /**
     * Method called to add specified annotation in the Map, but
     * only if it didn't yet exist.
     */
    public boolean addIfNotPresent(Annotation ann)
    {
        if (_annotations == null || !_annotations.containsKey(ann.annotationType())) {
            _add(ann);
            return true;
        }
        return false;
    }

    /**
     * Method called to add specified annotation in the Map.
     * 
     * @return True if the addition changed the contents, that is, this map did not
     *   already have specified annotation
     */
    public boolean add(Annotation ann) {
        return _add(ann);
    }

    @Override
    public String toString() {
        if (_annotations == null) {
            return "[null]";
        }
        return _annotations.toString();
    }

    /*
    /**********************************************************
    /* Helper methods
    /**********************************************************
     */

    protected final boolean _add(Annotation ann) {
        if (_annotations == null) {
            _annotations = new HashMap<Class<?>,Annotation>();
        }
        Annotation previous = _annotations.put(ann.annotationType(), ann);
        return (previous == null) || !previous.equals(ann);
    }
}

⏎ com/fasterxml/jackson/databind/introspect/AnnotationMap.java

Or download all of them as a single archive file:

File name: jackson-databind-2.14.0-sources.jar
File size: 1187952 bytes
Release date: 2022-11-05
Download 

⇒ Jackson Annotations Source Code

⇐ Download and Install Jackson Binary Package

⇑ Downloading and Reviewing jackson-*.jar

⇑⇑ Jackson - Java JSON library