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/jsontype/impl/StdSubtypeResolver.java

package com.fasterxml.jackson.databind.jsontype.impl;

import java.lang.reflect.Modifier;
import java.util.*;

import com.fasterxml.jackson.databind.AnnotationIntrospector;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.cfg.MapperConfig;
import com.fasterxml.jackson.databind.introspect.*;
import com.fasterxml.jackson.databind.jsontype.NamedType;
import com.fasterxml.jackson.databind.jsontype.SubtypeResolver;

/**
 * Standard {@link SubtypeResolver} implementation.
 */
public class StdSubtypeResolver
    extends SubtypeResolver
    implements java.io.Serializable
{
    private static final long serialVersionUID = 1L;

    protected LinkedHashSet<NamedType> _registeredSubtypes;

    public StdSubtypeResolver() { }

    // @since 2.12
    protected StdSubtypeResolver(StdSubtypeResolver src) {
        LinkedHashSet<NamedType> reg = src._registeredSubtypes;
        _registeredSubtypes = (reg == null) ? null
                : new LinkedHashSet<>(reg);
    }

    // @since 2.12
    @Override
    public SubtypeResolver copy() {
        return new StdSubtypeResolver(this);
    }

    /*
    /**********************************************************
    /* Subtype registration
    /**********************************************************
     */

    @Override    
    public void registerSubtypes(NamedType... types) {
        if (_registeredSubtypes == null) {
            _registeredSubtypes = new LinkedHashSet<NamedType>();
        }
        for (NamedType type : types) {
            _registeredSubtypes.add(type);
        }
    }

    @Override
    public void registerSubtypes(Class<?>... classes) {
        NamedType[] types = new NamedType[classes.length];
        for (int i = 0, len = classes.length; i < len; ++i) {
            types[i] = new NamedType(classes[i]);
        }
        registerSubtypes(types);
    }

    @Override // since 2.9
    public void registerSubtypes(Collection<Class<?>> subtypes) {
        int len = subtypes.size();
        NamedType[] types = new NamedType[len];
        int i = 0;
        for (Class<?> subtype : subtypes) {
            types[i++] = new NamedType(subtype);
        }
        registerSubtypes(types);
    }

    /*
    /**********************************************************
    /* Resolution by class (serialization)
    /**********************************************************
     */

    @Override
    public Collection<NamedType> collectAndResolveSubtypesByClass(MapperConfig<?> config, 
            AnnotatedMember property, JavaType baseType)
    {
        final AnnotationIntrospector ai = config.getAnnotationIntrospector();

        // for backwards compatibility, must allow null here:
        final Class<?> rawBase;
        if (baseType != null) {
            rawBase = baseType.getRawClass();
        } else if (property != null) {
            rawBase = property.getRawType();
        } else {
            throw new IllegalArgumentException("Both property and base type are nulls");
        }
        
        HashMap<NamedType, NamedType> collected = new HashMap<NamedType, NamedType>();
        // start with registered subtypes (which have precedence)
        if (_registeredSubtypes != null) {
            for (NamedType subtype : _registeredSubtypes) {
                // is it a subtype of root type?
                if (rawBase.isAssignableFrom(subtype.getType())) { // yes
                    AnnotatedClass curr = AnnotatedClassResolver.resolveWithoutSuperTypes(config,
                            subtype.getType());
                    _collectAndResolve(curr, subtype, config, ai, collected);
                }
            }
        }
        
        // then annotated types for property itself
        if (property != null) {
            Collection<NamedType> st = ai.findSubtypes(property);
            if (st != null) {
                for (NamedType nt : st) {
                    AnnotatedClass ac = AnnotatedClassResolver.resolveWithoutSuperTypes(config,
                            nt.getType());
                    _collectAndResolve(ac, nt, config, ai, collected);
                }            
            }
        }

        NamedType rootType = new NamedType(rawBase, null);
        AnnotatedClass ac = AnnotatedClassResolver.resolveWithoutSuperTypes(config, rawBase);
            
        // and finally subtypes via annotations from base type (recursively)
        _collectAndResolve(ac, rootType, config, ai, collected);

        return new ArrayList<NamedType>(collected.values());
    }

    @Override
    public Collection<NamedType> collectAndResolveSubtypesByClass(MapperConfig<?> config,
            AnnotatedClass type)
    {
        final AnnotationIntrospector ai = config.getAnnotationIntrospector();
        HashMap<NamedType, NamedType> subtypes = new HashMap<>();

        // then consider registered subtypes (which have precedence over annotations)
        if (_registeredSubtypes != null) {
            Class<?> rawBase = type.getRawType();
            for (NamedType subtype : _registeredSubtypes) {
                // is it a subtype of root type?
                if (rawBase.isAssignableFrom(subtype.getType())) { // yes
                    AnnotatedClass curr = AnnotatedClassResolver.resolveWithoutSuperTypes(config,
                            subtype.getType());
                    _collectAndResolve(curr, subtype, config, ai, subtypes);
                }
            }
        }
        // and then check subtypes via annotations from base type (recursively)
        NamedType rootType = new NamedType(type.getRawType(), null);
        _collectAndResolve(type, rootType, config, ai, subtypes);
        return new ArrayList<NamedType>(subtypes.values());
    }

    /*
    /**********************************************************
    /* Resolution by class (deserialization)
    /**********************************************************
     */

    @Override
    public Collection<NamedType> collectAndResolveSubtypesByTypeId(MapperConfig<?> config, 
            AnnotatedMember property, JavaType baseType)
    {
        final AnnotationIntrospector ai = config.getAnnotationIntrospector();
        Class<?> rawBase = baseType.getRawClass();

        // Need to keep track of classes that have been handled already 
        Set<Class<?>> typesHandled = new HashSet<Class<?>>();
        Map<String,NamedType> byName = new LinkedHashMap<String,NamedType>();

        // start with lowest-precedence, which is from type hierarchy
        NamedType rootType = new NamedType(rawBase, null);
        AnnotatedClass ac = AnnotatedClassResolver.resolveWithoutSuperTypes(config,
                rawBase);
        _collectAndResolveByTypeId(ac, rootType, config, typesHandled, byName);
        
        // then with definitions from property
        if (property != null) {
            Collection<NamedType> st = ai.findSubtypes(property);
            if (st != null) {
                for (NamedType nt : st) {
                    ac = AnnotatedClassResolver.resolveWithoutSuperTypes(config, nt.getType());
                    _collectAndResolveByTypeId(ac, nt, config, typesHandled, byName);
                }            
            }
        }
        // and finally explicit type registrations (highest precedence)
        if (_registeredSubtypes != null) {
            for (NamedType subtype : _registeredSubtypes) {
                // is it a subtype of root type?
                if (rawBase.isAssignableFrom(subtype.getType())) { // yes
                    AnnotatedClass curr = AnnotatedClassResolver.resolveWithoutSuperTypes(config,
                            subtype.getType());
                    _collectAndResolveByTypeId(curr, subtype, config, typesHandled, byName);
                }
            }
        }
        return _combineNamedAndUnnamed(rawBase, typesHandled, byName);
    }

    @Override
    public Collection<NamedType> collectAndResolveSubtypesByTypeId(MapperConfig<?> config,
            AnnotatedClass baseType)
    {
        final Class<?> rawBase = baseType.getRawType();
        Set<Class<?>> typesHandled = new HashSet<Class<?>>();
        Map<String,NamedType> byName = new LinkedHashMap<String,NamedType>();

        NamedType rootType = new NamedType(rawBase, null);
        _collectAndResolveByTypeId(baseType, rootType, config, typesHandled, byName);
        
        if (_registeredSubtypes != null) {
            for (NamedType subtype : _registeredSubtypes) {
                // is it a subtype of root type?
                if (rawBase.isAssignableFrom(subtype.getType())) { // yes
                    AnnotatedClass curr = AnnotatedClassResolver.resolveWithoutSuperTypes(config,
                            subtype.getType());
                    _collectAndResolveByTypeId(curr, subtype, config, typesHandled, byName);
                }
            }
        }
        return _combineNamedAndUnnamed(rawBase, typesHandled, byName);
    }

    /*
    /**********************************************************
    /* Internal methods
    /**********************************************************
     */

    /**
     * Method called to find subtypes for a specific type (class), using
     * type (class) as the unique key (in case of conflicts).
     */
    protected void _collectAndResolve(AnnotatedClass annotatedType, NamedType namedType,
            MapperConfig<?> config, AnnotationIntrospector ai,
            HashMap<NamedType, NamedType> collectedSubtypes)
    {
        if (!namedType.hasName()) {
            String name = ai.findTypeName(annotatedType);
            if (name != null) {
                namedType = new NamedType(namedType.getType(), name);
            }
        }

        //For Serialization we only want to return a single NamedType per class so it's
        //unambiguous what name we use.
        NamedType typeOnlyNamedType = new NamedType(namedType.getType());

        // First things first: is base type itself included?
        if (collectedSubtypes.containsKey(typeOnlyNamedType)) {
            // if so, no recursion; however, may need to update name?
            if (namedType.hasName()) {
                NamedType prev = collectedSubtypes.get(typeOnlyNamedType);
                if (!prev.hasName()) {
                    collectedSubtypes.put(typeOnlyNamedType, namedType);
                }
            }
            return;
        }
        // if it wasn't, add and check subtypes recursively
        collectedSubtypes.put(typeOnlyNamedType, namedType);
        Collection<NamedType> st = ai.findSubtypes(annotatedType);
        if (st != null && !st.isEmpty()) {
            for (NamedType subtype : st) {
                AnnotatedClass subtypeClass = AnnotatedClassResolver.resolveWithoutSuperTypes(config,
                        subtype.getType());
                _collectAndResolve(subtypeClass, subtype, config, ai, collectedSubtypes);
            }
        }
    }

    /**
     * Method called to find subtypes for a specific type (class), using
     * type id as the unique key (in case of conflicts).
     */
    protected void _collectAndResolveByTypeId(AnnotatedClass annotatedType, NamedType namedType,
            MapperConfig<?> config,
            Set<Class<?>> typesHandled, Map<String,NamedType> byName)
    {
        final AnnotationIntrospector ai = config.getAnnotationIntrospector();
        if (!namedType.hasName()) {
            String name = ai.findTypeName(annotatedType);
            if (name != null) {
                namedType = new NamedType(namedType.getType(), name);
            }
        }
        if (namedType.hasName()) {
            byName.put(namedType.getName(), namedType);
        }

        // only check subtypes if this type hadn't yet been handled
        if (typesHandled.add(namedType.getType())) {
            Collection<NamedType> st = ai.findSubtypes(annotatedType);
            if (st != null && !st.isEmpty()) {
                for (NamedType subtype : st) {
                    AnnotatedClass subtypeClass = AnnotatedClassResolver.resolveWithoutSuperTypes(config,
                            subtype.getType());
                    _collectAndResolveByTypeId(subtypeClass, subtype, config, typesHandled, byName);
                }
            }
        }
    }

    /**
     * Helper method used for merging explicitly named types and handled classes
     * without explicit names.
     */
    protected Collection<NamedType> _combineNamedAndUnnamed(Class<?> rawBase,
            Set<Class<?>> typesHandled, Map<String,NamedType> byName)
    {
        ArrayList<NamedType> result = new ArrayList<NamedType>(byName.values());

        // Ok, so... we will figure out which classes have no explicitly assigned name,
        // by removing Classes from Set. And for remaining classes, add an anonymous
        // marker
        for (NamedType t : byName.values()) {
            typesHandled.remove(t.getType());
        }
        for (Class<?> cls : typesHandled) {
            // 27-Apr-2017, tatu: [databind#1616] Do not add base type itself unless
            //     it is concrete (or has explicit type name)
            if ((cls == rawBase) && Modifier.isAbstract(cls.getModifiers())) {
                continue;
            }
            result.add(new NamedType(cls));
        }
        return result;
    }
}

⏎ com/fasterxml/jackson/databind/jsontype/impl/StdSubtypeResolver.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
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