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/util/VersionUtil.java

package com.fasterxml.jackson.core.util;

import java.io.*;
import java.util.Properties;
import java.util.regex.Pattern;

import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.core.Versioned;

/**
 * Functionality for supporting exposing of component {@link Version}s.
 * Also contains other misc methods that have no other place to live in.
 *<p>
 * Note that this class can be used in two roles: first, as a static
 * utility class for loading purposes, and second, as a singleton
 * loader of per-module version information.
 *<p>
 * Note that method for accessing version information changed between versions
 * 2.1 and 2.2; earlier code used file named "VERSION.txt"; but this has serious
 * performance issues on some platforms (Android), so a replacement system
 * was implemented to use class generation and dynamic class loading.
 *<p>
 * Note that functionality for reading "VERSION.txt" was removed completely
 * from Jackson 2.6.
 */
public class VersionUtil
{
    private final static Pattern V_SEP = Pattern.compile("[-_./;:]");

    /*
    /**********************************************************************
    /* Instance life-cycle
    /**********************************************************************
     */

    protected VersionUtil() { }

    @Deprecated // since 2.9
    public Version version() { return Version.unknownVersion(); }

    /*
    /**********************************************************************
    /* Static load methods
    /**********************************************************************
     */
    
    /**
     * Loads version information by introspecting a class named
     * "PackageVersion" in the same package as the given class.
     *<p>
     * If the class could not be found or does not have a public
     * static Version field named "VERSION", returns "empty" {@link Version}
     * returned by {@link Version#unknownVersion()}.
     *
     * @param cls Class for which to look version information
     *
     * @return Version information discovered if any; 
     *  {@link Version#unknownVersion()} if none
     */
    public static Version versionFor(Class<?> cls)
    {
        Version v = null;
        try {
            String versionInfoClassName = cls.getPackage().getName() + ".PackageVersion";
            Class<?> vClass = Class.forName(versionInfoClassName, true, cls.getClassLoader());
            // However, if class exists, it better work correctly, no swallowing exceptions
            try {
                v = ((Versioned) vClass.getDeclaredConstructor().newInstance()).version();
            } catch (Exception e) {
                throw new IllegalArgumentException("Failed to get Versioned out of "+vClass);
            }
        } catch (Exception e) { // ok to be missing (not good but acceptable)
            ;
        }
        return (v == null) ? Version.unknownVersion() : v;
    }

    /**
     * Alias of {@link #versionFor(Class)}.
     *
     * @param cls Class for which to look version information
     *
     * @return Version information discovered if any; 
     *  {@link Version#unknownVersion()} if none
     *
     * @deprecated Since 2.12 simply use {@link #versionFor(Class)} instead
     */
    @Deprecated
    public static Version packageVersionFor(Class<?> cls) {
        return versionFor(cls);
    }

    /**
     * Will attempt to load the maven version for the given groupId and
     * artifactId.  Maven puts a pom.properties file in
     * META-INF/maven/groupId/artifactId, containing the groupId,
     * artifactId and version of the library.
     *
     * @param cl the ClassLoader to load the pom.properties file from
     * @param groupId the groupId of the library
     * @param artifactId the artifactId of the library
     * @return The version
     * 
     * @deprecated Since 2.6: functionality not used by any official Jackson component, should be
     *   moved out if anyone needs it
     */
    @SuppressWarnings("resource")
    @Deprecated // since 2.6
    public static Version mavenVersionFor(ClassLoader cl, String groupId, String artifactId)
    {
        InputStream pomProperties = cl.getResourceAsStream("META-INF/maven/"
                + groupId.replaceAll("\\.", "/")+ "/" + artifactId + "/pom.properties");
        if (pomProperties != null) {
            try {
                Properties props = new Properties();
                props.load(pomProperties);
                String versionStr = props.getProperty("version");
                String pomPropertiesArtifactId = props.getProperty("artifactId");
                String pomPropertiesGroupId = props.getProperty("groupId");
                return parseVersion(versionStr, pomPropertiesGroupId, pomPropertiesArtifactId);
            } catch (IOException e) {
                // Ignore
            } finally {
                _close(pomProperties);
            }
        }
        return Version.unknownVersion();
    }

    /**
     * Method used by <code>PackageVersion</code> classes to decode version injected by Maven build.
     *
     * @param s Version String to parse
     * @param groupId Maven group id to include with version
     * @param artifactId Maven artifact id to include with version
     *
     * @return Version instance constructed from parsed components, if successful;
     *    {@link Version#unknownVersion()} if parsing of components fail
     */
    public static Version parseVersion(String s, String groupId, String artifactId)
    {
        if (s != null && (s = s.trim()).length() > 0) {
            String[] parts = V_SEP.split(s);
            return new Version(parseVersionPart(parts[0]),
                    (parts.length > 1) ? parseVersionPart(parts[1]) : 0,
                    (parts.length > 2) ? parseVersionPart(parts[2]) : 0,
                    (parts.length > 3) ? parts[3] : null,
                    groupId, artifactId);
        }
        return Version.unknownVersion();
    }

    protected static int parseVersionPart(String s) {
        int number = 0;
        for (int i = 0, len = s.length(); i < len; ++i) {
            char c = s.charAt(i);
            if (c > '9' || c < '0') break;
            number = (number * 10) + (c - '0');
        }
        return number;
    }

    private final static void _close(Closeable c) {
        try {
            c.close();
        } catch (IOException e) { }
    }

    /*
    /**********************************************************************
    /* Orphan utility methods
    /**********************************************************************
     */

    public final static void throwInternal() {
        throw new RuntimeException("Internal error: this code path should never get executed");
    }
}

⏎ com/fasterxml/jackson/core/util/VersionUtil.java

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