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-2.12.4-sources.jar). You can download it at Jackson Maven Website.

You can also browse Jackson Databind Source Code below:

⏎ com/fasterxml/jackson/databind/jdk14/JDK14Util.java

package com.fasterxml.jackson.databind.jdk14;

import java.lang.reflect.Method;
import java.util.Collections;
import java.util.List;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonCreator.Mode;
import com.fasterxml.jackson.databind.AnnotationIntrospector;
import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.introspect.AnnotatedConstructor;
import com.fasterxml.jackson.databind.util.ClassUtil;

/**
 * Helper class to support some of JDK 14 (and later) features
 * without Jackson itself being run on (or even built with) Java 14.
 * In particular allows better support of {@code java.lang.Record}
 * types (see <a href="https://openjdk.java.net/jeps/359">JEP 359</a>).
 *
 * @since 2.12
 */
public class JDK14Util
{
    public static String[] getRecordFieldNames(Class<?> recordType) {
        return RecordAccessor.instance().getRecordFieldNames(recordType);
    }

    public static AnnotatedConstructor findRecordConstructor(DeserializationContext ctxt,
            BeanDescription beanDesc, List<String> names) {
        return new CreatorLocator(ctxt, beanDesc)
            .locate(names);
    }

    static class RecordAccessor {
        private final Method RECORD_GET_RECORD_COMPONENTS;
        private final Method RECORD_COMPONENT_GET_NAME;
        private final Method RECORD_COMPONENT_GET_TYPE;

        private final static RecordAccessor INSTANCE;
        private final static RuntimeException PROBLEM;

        static {
            RuntimeException prob = null;
            RecordAccessor inst = null;
            try {
                inst = new RecordAccessor();
            } catch (RuntimeException e) {
                prob = e;
            }
            INSTANCE = inst;
            PROBLEM = prob;
        }

        private RecordAccessor() throws RuntimeException {
            try {
                RECORD_GET_RECORD_COMPONENTS = Class.class.getMethod("getRecordComponents");
                Class<?> c = Class.forName("java.lang.reflect.RecordComponent");
                RECORD_COMPONENT_GET_NAME = c.getMethod("getName");
                RECORD_COMPONENT_GET_TYPE = c.getMethod("getType");
            } catch (Exception e) {
                throw new RuntimeException(String.format(
"Failed to access Methods needed to support `java.lang.Record`: (%s) %s",
e.getClass().getName(), e.getMessage()), e);
            }
        }

        public static RecordAccessor instance() {
            if (PROBLEM != null) {
                throw PROBLEM;
            }
            return INSTANCE;
        }

        public String[] getRecordFieldNames(Class<?> recordType) throws IllegalArgumentException
        {
            final Object[] components = recordComponents(recordType);
            final String[] names = new String[components.length];
            for (int i = 0; i < components.length; i++) {
                try {
                    names[i] = (String) RECORD_COMPONENT_GET_NAME.invoke(components[i]);
                } catch (Exception e) {
                    throw new IllegalArgumentException(String.format(
"Failed to access name of field #%d (of %d) of Record type %s",
i, components.length, ClassUtil.nameOf(recordType)), e);
                }
            }
            return names;
        }

        public RawTypeName[] getRecordFields(Class<?> recordType) throws IllegalArgumentException
        {
            final Object[] components = recordComponents(recordType);
            final RawTypeName[] results = new RawTypeName[components.length];
            for (int i = 0; i < components.length; i++) {
                String name;
                try {
                    name = (String) RECORD_COMPONENT_GET_NAME.invoke(components[i]);
                } catch (Exception e) {
                    throw new IllegalArgumentException(String.format(
"Failed to access name of field #%d (of %d) of Record type %s",
i, components.length, ClassUtil.nameOf(recordType)), e);
                }
                Class<?> type;
                try {
                    type = (Class<?>) RECORD_COMPONENT_GET_TYPE.invoke(components[i]);
                } catch (Exception e) {
                    throw new IllegalArgumentException(String.format(
"Failed to access type of field #%d (of %d) of Record type %s",
i, components.length, ClassUtil.nameOf(recordType)), e);
                }
                results[i] = new RawTypeName(type, name);
            }
            return results;
        }

        protected Object[] recordComponents(Class<?> recordType) throws IllegalArgumentException
        {
            try {
                return (Object[]) RECORD_GET_RECORD_COMPONENTS.invoke(recordType);
            } catch (Exception e) {
                throw new IllegalArgumentException("Failed to access RecordComponents of type "
                        +ClassUtil.nameOf(recordType));
            }
        }
    }

    static class RawTypeName {
        public final Class<?> rawType;
        public final String name;

        public RawTypeName(Class<?> rt, String n) {
            rawType = rt;
            name = n;
        }
    }

    static class CreatorLocator {
        protected final BeanDescription _beanDesc;
        protected final DeserializationConfig _config;
        protected final AnnotationIntrospector _intr;

        protected final List<AnnotatedConstructor> _constructors;
        protected final AnnotatedConstructor _primaryConstructor;
        protected final RawTypeName[] _recordFields;

        CreatorLocator(DeserializationContext ctxt, BeanDescription beanDesc)
        {
            _beanDesc = beanDesc;

            _intr = ctxt.getAnnotationIntrospector();
            _config = ctxt.getConfig();

            _recordFields = RecordAccessor.instance().getRecordFields(beanDesc.getBeanClass());
            final int argCount = _recordFields.length;

            // And then locate the canonical constructor; must be found, if not, fail
            // altogether (so we can figure out what went wrong)
            AnnotatedConstructor primary = null;

            // One special case: empty Records, empty constructor is separate case
            if (argCount == 0) {
                primary = beanDesc.findDefaultConstructor();
                _constructors = Collections.singletonList(primary);
            } else {
                _constructors = beanDesc.getConstructors();
                main_loop:
                for (AnnotatedConstructor ctor : _constructors) {
                    if (ctor.getParameterCount() != argCount) {
                        continue;
                    }
                    for (int i = 0; i < argCount; ++i) {
                        if (!ctor.getRawParameterType(i).equals(_recordFields[i].rawType)) {
                            continue main_loop;
                        }
                    }
                    primary = ctor;
                    break;
                }
            }
            if (primary == null) {
                throw new IllegalArgumentException("Failed to find the canonical Record constructor of type "
                        +ClassUtil.getTypeDescription(_beanDesc.getType()));
            }
            _primaryConstructor = primary;
        }

        public AnnotatedConstructor locate(List<String> names)
        {
            // First things first: ensure that either there are no explicit marked constructors
            // or that there is just one and it is the canonical one and it is not
            // declared as "delegating" constructor
            for (AnnotatedConstructor ctor : _constructors) {
                JsonCreator.Mode creatorMode = _intr.findCreatorAnnotation(_config, ctor);
                if ((null == creatorMode) || (Mode.DISABLED == creatorMode)) {
                    continue;
                }
                // If there's a delegating Creator let caller figure out
                if (Mode.DELEGATING == creatorMode) {
                    return null;
                }
                if (ctor != _primaryConstructor) {
                    return null;
                }
            }

            // By now we have established that the canonical constructor is the one to use
            // and just need to gather implicit names to return
            for (RawTypeName field : _recordFields) {
                names.add(field.name);
            }
            return _primaryConstructor;
        }
    }
}

⏎ com/fasterxml/jackson/databind/jdk14/JDK14Util.java

 

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