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Hutool 扩展工具类（提供其它类库的封装）
There is a newer version: 5.8.33
package cn.hutool.extra.template.engine.freemarker;

import cn.hutool.core.io.FileUtil;
import cn.hutool.core.io.IORuntimeException;
import cn.hutool.core.util.ClassUtil;
import cn.hutool.extra.template.Template;
import cn.hutool.extra.template.TemplateConfig;
import cn.hutool.extra.template.TemplateEngine;
import cn.hutool.extra.template.TemplateException;
import freemarker.cache.ClassTemplateLoader;
import freemarker.cache.FileTemplateLoader;
import freemarker.template.Configuration;

import java.io.IOException;

/**
 * FreeMarker模板引擎封装

 * 见：https://freemarker.apache.org/
 *
 * @author looly
 */
public class FreemarkerEngine implements TemplateEngine {

	private Configuration cfg;

	// --------------------------------------------------------------------------------- Constructor start

	/**
	 * 默认构造
	 */
	public FreemarkerEngine() {
	}

	/**
	 * 构造
	 *
	 * @param config 模板配置
	 */
	public FreemarkerEngine(TemplateConfig config) {
		init(config);
	}

	/**
	 * 构造
	 *
	 * @param freemarkerCfg {@link Configuration}
	 */
	public FreemarkerEngine(Configuration freemarkerCfg) {
		init(freemarkerCfg);
	}
	// --------------------------------------------------------------------------------- Constructor end

	@Override
	public TemplateEngine init(TemplateConfig config) {
		if (null == config) {
			config = TemplateConfig.DEFAULT;
		}
		init(createCfg(config));
		return this;
	}

	/**
	 * 初始化引擎
	 *
	 * @param freemarkerCfg Configuration
	 */
	private void init(Configuration freemarkerCfg) {
		this.cfg = freemarkerCfg;
	}

	@Override
	public Template getTemplate(String resource) {
		if (null == this.cfg) {
			init(TemplateConfig.DEFAULT);
		}
		try {
			return FreemarkerTemplate.wrap(this.cfg.getTemplate(resource));
		} catch (IOException e) {
			throw new IORuntimeException(e);
		} catch (Exception e) {
			throw new TemplateException(e);
		}
	}

	/**
	 * 获取原始引擎的钩子方法，用于自定义特殊属性，如插件等
	 *
	 * @return {@link Configuration}
	 * @since 5.8.7
	 */
	public Configuration getConfiguration() {
		return this.cfg;
	}

	/**
	 * 创建配置项
	 *
	 * @param config 模板配置
	 * @return {@link Configuration }
	 */
	private static Configuration createCfg(TemplateConfig config) {
		if (null == config) {
			config = new TemplateConfig();
		}

		final Configuration cfg = new Configuration(Configuration.DEFAULT_INCOMPATIBLE_IMPROVEMENTS);
		cfg.setLocalizedLookup(false);
		cfg.setDefaultEncoding(config.getCharset().toString());

		switch (config.getResourceMode()) {
			case CLASSPATH:
				cfg.setTemplateLoader(new ClassTemplateLoader(ClassUtil.getClassLoader(), config.getPath()));
				break;
			case FILE:
				try {
					cfg.setTemplateLoader(new FileTemplateLoader(FileUtil.file(config.getPath())));
				} catch (IOException e) {
					throw new IORuntimeException(e);
				}
				break;
			case WEB_ROOT:
				try {
					cfg.setTemplateLoader(new FileTemplateLoader(FileUtil.file(FileUtil.getWebRoot(), config.getPath())));
				} catch (IOException e) {
					throw new IORuntimeException(e);
				}
				break;
			case STRING:
				cfg.setTemplateLoader(new SimpleStringTemplateLoader());
				break;
			default:
				break;
		}

		return cfg;
	}
}