protected void loadDetachedPlugins()

in core/src/main/java/hudson/PluginManager.java [749:823]
58 lines of code
14 McCabe index (conditional complexity)

    protected void loadDetachedPlugins() {
        VersionNumber lastExecVersion = new VersionNumber(InstallUtil.getLastExecVersion());
        if (lastExecVersion.isNewerThan(InstallUtil.NEW_INSTALL_VERSION) && lastExecVersion.isOlderThan(Jenkins.getVersion())) {

            LOGGER.log(INFO, "Upgrading Jenkins. The last running version was {0}. This Jenkins is version {1}.",
                    new Object[] {lastExecVersion, Jenkins.VERSION});

            final List<DetachedPluginsUtil.DetachedPlugin> detachedPlugins = DetachedPluginsUtil.getDetachedPlugins(lastExecVersion);

            Set<String> loadedDetached = loadPluginsFromWar("/WEB-INF/detached-plugins", new FilenameFilter() {
                @Override
                public boolean accept(File dir, String name) {
                    name = normalisePluginName(name);

                    // If this was a plugin that was detached some time in the past i.e. not just one of the
                    // plugins that was bundled "for fun".
                    if (DetachedPluginsUtil.isDetachedPlugin(name)) {
                        VersionNumber installedVersion = getPluginVersion(rootDir, name);
                        VersionNumber bundledVersion = getPluginVersion(dir, name);
                        // If the plugin is already installed, we need to decide whether to replace it with the bundled version.
                        if (installedVersion != null && bundledVersion != null) {
                            // If the installed version is older than the bundled version, then it MUST be upgraded.
                            // If the installed version is newer than the bundled version, then it MUST NOT be upgraded.
                            // If the versions are equal we just keep the installed version.
                            return installedVersion.isOlderThan(bundledVersion);
                        }
                    }

                    // If it's a plugin that was detached since the last running version.
                    for (DetachedPluginsUtil.DetachedPlugin detachedPlugin : detachedPlugins) {
                        if (detachedPlugin.getShortName().equals(name)) {
                            return true;
                        }
                    }

                    // Otherwise skip this and do not install.
                    return false;
                }
            });

            LOGGER.log(INFO, "Upgraded Jenkins from version {0} to version {1}. Loaded detached plugins (and dependencies): {2}",
                    new Object[] {lastExecVersion, Jenkins.VERSION, loadedDetached});

            InstallUtil.saveLastExecVersion();
        } else {
            final Set<DetachedPluginsUtil.DetachedPlugin> forceUpgrade = new HashSet<>();
            // TODO using getDetachedPlugins here seems wrong; should be forcing an upgrade when the installed version is older than that in WEB-INF/detached-plugins/
            for (DetachedPluginsUtil.DetachedPlugin p : DetachedPluginsUtil.getDetachedPlugins()) {
                VersionNumber installedVersion = getPluginVersion(rootDir, p.getShortName());
                VersionNumber requiredVersion = p.getRequiredVersion();
                if (installedVersion != null && installedVersion.isOlderThan(requiredVersion)) {
                    LOGGER.log(Level.WARNING,
                            "Detached plugin {0} found at version {1}, required minimum version is {2}",
                            new Object[]{p.getShortName(), installedVersion, requiredVersion});
                    forceUpgrade.add(p);
                }
            }
            if (!forceUpgrade.isEmpty()) {
                Set<String> loadedDetached = loadPluginsFromWar("/WEB-INF/detached-plugins", new FilenameFilter() {
                    @Override
                    public boolean accept(File dir, String name) {
                        name = normalisePluginName(name);
                        for (DetachedPluginsUtil.DetachedPlugin detachedPlugin : forceUpgrade) {
                            if (detachedPlugin.getShortName().equals(name)) {
                                return true;
                            }
                        }
                        return false;
                    }
                });
                LOGGER.log(INFO, "Upgraded detached plugins (and dependencies): {0}",
                        new Object[]{loadedDetached});
            }
        }
    }