模板渲染 - Freemarker

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模板引擎除了去做后端应用的页面渲染，很多时候也可以用来生成一些代码，例如利用sql生成pojo对象，生成模板页面等
这里简单记录一下FreeMarker渲染模板时最基本的代码

  1. 引入FreeMarker Maven信息

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    <dependency>
        <groupId>org.freemarker</groupId>
        <artifactId>freemarker</artifactId>
        <version>2.3.26-incubating</version>
    </dependency>

  2. 实现代码

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    import com.google.common.base.Charsets;
    import com.github.pdf.tools.exception.FreeMarkerException;
    import freemarker.cache.FileTemplateLoader;
    import freemarker.template.Configuration;
    import freemarker.template.Template;
    import freemarker.template.TemplateExceptionHandler;

    import java.io.File;
    import java.io.IOException;
    import java.io.StringWriter;
    import java.util.Map;
    import java.util.concurrent.ConcurrentHashMap;

    /**
     * @author wangdongbo
     * @since 2019/7/3.
     */
    public class FreeMarkerTemplate extends AbstractTemplate {

        private static Map<String, FileTemplateLoader> FILE_TEMPLATE_LOADER_CACHE = new ConcurrentHashMap<>(16);

        private static Map<String, Configuration> CONFIGURATION_CACHE = new ConcurrentHashMap<>(16);

        private static Configuration getConfiguration(String templatePath) {
            if (CONFIGURATION_CACHE.get(templatePath) != null) {
                return CONFIGURATION_CACHE.get(templatePath);
            }
            Configuration config = new Configuration(Configuration.VERSION_2_3_25);
            config.setDefaultEncoding(Charsets.UTF_8.toString());
            config.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);
            config.setLogTemplateExceptions(false);
            FileTemplateLoader fileTemplateLoader;
            try {
                if (FILE_TEMPLATE_LOADER_CACHE.containsKey(templatePath)) {
                    fileTemplateLoader = FILE_TEMPLATE_LOADER_CACHE.get(templatePath);
                } else {
                    fileTemplateLoader = new FileTemplateLoader(new File(templatePath));
                }
            } catch (IOException e) {
                throw new FreeMarkerException("fileTemplateLoader init error!", e);
            }
            config.setTemplateLoader(fileTemplateLoader);
            CONFIGURATION_CACHE.put(templatePath, config);
            return config;
        }

        @Override
        protected String getContent(String templatePath, String templateName, Object data) {
            try {
                Template template = getConfiguration(templatePath).getTemplate(templateName);
                StringWriter writer = new StringWriter();
                template.process(data, writer);
                writer.flush();
                return writer.toString();
            } catch (Exception ex) {
                throw new FreeMarkerException("FreeMarkerUtil process fail", ex);
            }
        }

    }