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

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

You can also browse Jackson Core Source Code below:

⏎ com/fasterxml/jackson/core/TreeCodec.java

package com.fasterxml.jackson.core;

import java.io.IOException;

/**
 * Interface that defines objects that can read and write
 * {@link TreeNode} instances using Streaming API.
 * 
 * @since 2.3
 */
public abstract class TreeCodec
{
    public abstract <T extends TreeNode> T readTree(JsonParser p) throws IOException, JsonProcessingException;
    public abstract void writeTree(JsonGenerator g, TreeNode tree) throws IOException, JsonProcessingException;

    /**
     * @return Node that represents "missing" node during traversal: something
     *   referenced but that does not exist in content model
     * 
     * @since 2.10
     */
    public TreeNode missingNode() {
        return null;
    }

    /**
     * @return Node that represents explict {@code null} value in content
     * 
     * @since 2.10
     */
    public TreeNode nullNode() {
        return null;
    }

    public abstract TreeNode createArrayNode();
    public abstract TreeNode createObjectNode();
    public abstract JsonParser treeAsTokens(TreeNode node);
}

⏎ com/fasterxml/jackson/core/TreeCodec.java

Or download all of them as a single archive file:

File name: jackson-core-2.14.0-sources.jar
File size: 497693 bytes
Release date: 2022-11-05
Download 

⇒ Download and Install Jackson Binary Package

⇐ What Is Jackson

⇑ Downloading and Reviewing jackson-*.jar

⇑⇑ Jackson - Java JSON library