Spring-Boot with JSP Tag Libs in embedded Tomcat

Question

I am currently migrating a Spring MVC Webapp (xml-config to java-config, tomcat to embedded tomcat via spring-boot).

The webapp uses freemarker as templating engine

Answer 1

This really should be built-in.

First, disable the built in FreeMarkerAutoConfiguration on your Application:

@SpringBootApplication
@EnableAutoConfiguration(exclude = {FreeMarkerAutoConfiguration.class})
public class Application extends WebMvcConfigurerAdapter {
    ...
]

Then add this custom configuration:

(adapted from https://github.com/isopov/fan/blob/master/fan-web/src/main/java/com/sopovs/moradanen/fan/WebApplicationConfiguration.java; Added an ObjectWrapper to the TaglibFactory and removed the addResourceHandlers() override)

import freemarker.cache.ClassTemplateLoader;
import freemarker.ext.jsp.TaglibFactory;
import freemarker.template.TemplateException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.ReloadableResourceBundleMessageSource;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
import org.springframework.web.servlet.i18n.LocaleChangeInterceptor;
import org.springframework.web.servlet.i18n.SessionLocaleResolver;
import org.springframework.web.servlet.view.freemarker.FreeMarkerConfig;
import org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer;
import org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver;

import javax.servlet.ServletContext;
import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Locale;
import java.util.Properties;

@Configuration
public class CustomFreemarkerConfiguration extends WebMvcConfigurerAdapter {


    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        LocaleChangeInterceptor localeChangeInterceptor = new LocaleChangeInterceptor();
        localeChangeInterceptor.setParamName("lang");
        registry.addInterceptor(localeChangeInterceptor);
    }

    @Bean
    public ReloadableResourceBundleMessageSource messageSource() {
        ReloadableResourceBundleMessageSource messageSource = new ReloadableResourceBundleMessageSource();
        messageSource.setBasename("classpath:messages");
        messageSource.setFallbackToSystemLocale(false);
        messageSource.setDefaultEncoding("UTF-8");
        return messageSource;
    }

    @Bean
    public SessionLocaleResolver localeResolver() {
        SessionLocaleResolver localeResolver = new SessionLocaleResolver();
        localeResolver.setDefaultLocale(Locale.ENGLISH);
        return localeResolver;
    }

    @Bean
    @Autowired
    public freemarker.template.Configuration freeMarkerConfig(ServletContext servletContext) throws IOException,
            TemplateException {
        FreeMarkerConfigurer freemarkerConfig = configFreeMarkerConfigurer(servletContext);
        return freemarkerConfig.getConfiguration();
    }

    @Bean
    @Autowired
    public TaglibFactory taglibFactory(ServletContext servletContext) throws IOException, TemplateException {
        FreeMarkerConfigurer freemarkerConfig = configFreeMarkerConfigurer(servletContext);
        TaglibFactory taglibFactory = freemarkerConfig.getTaglibFactory();
        taglibFactory.setObjectWrapper(freemarker.template.Configuration.getDefaultObjectWrapper(freemarker.template.Configuration.getVersion()));
        return taglibFactory;
    }

    @Autowired
    @Bean
    public FreeMarkerConfig springFreeMarkerConfig(ServletContext servletContext) throws IOException, TemplateException {
        return new MyFreeMarkerConfig(freeMarkerConfig(servletContext), taglibFactory(servletContext));
    }

    private static FreeMarkerConfigurer configFreeMarkerConfigurer(ServletContext servletContext) throws IOException,
            TemplateException {
        FreeMarkerConfigurer freemarkerConfig = new FreeMarkerConfigurer();
        freemarkerConfig
                .setPreTemplateLoaders(new ClassTemplateLoader(CustomFreemarkerConfiguration.class, "/templates/"));
        ServletContext servletContextProxy = (ServletContext) Proxy.newProxyInstance(
                ServletContextResourceHandler.class.getClassLoader(),
                new Class[] { ServletContext.class },
                new ServletContextResourceHandler(servletContext));
        freemarkerConfig.setServletContext(servletContextProxy);
        Properties settings = new Properties();
        settings.put("default_encoding", "UTF-8");
        freemarkerConfig.setFreemarkerSettings(settings);
        freemarkerConfig.afterPropertiesSet();
        return freemarkerConfig;
    }

    @Bean
    public FreeMarkerViewResolver viewResolver() {
        FreeMarkerViewResolver viewResolver = new FreeMarkerViewResolver();
        viewResolver.setCache(false);
        viewResolver.setSuffix(".ftl");
        viewResolver.setContentType("text/html;charset=UTF-8");
        return viewResolver;
    }


    private static class ServletContextResourceHandler implements InvocationHandler
    {

        private final ServletContext target;

        private ServletContextResourceHandler(ServletContext target) {
            this.target = target;
        }

        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            if ("getResourceAsStream".equals(method.getName())) {
                Object result = method.invoke(target, args);
                if (result == null) {
                    result = CustomFreemarkerConfiguration.class.getResourceAsStream((String) args[0]);
                }
                return result;
            } else if ("getResource".equals(method.getName())) {
                Object result = method.invoke(target, args);
                if (result == null) {
                    result = CustomFreemarkerConfiguration.class.getResource((String) args[0]);
                }
                return result;
            }

            return method.invoke(target, args);
        }
    }

    private static class MyFreeMarkerConfig implements FreeMarkerConfig {

        private final freemarker.template.Configuration configuration;
        private final TaglibFactory taglibFactory;

        private MyFreeMarkerConfig(freemarker.template.Configuration configuration, TaglibFactory taglibFactory) {
            this.configuration = configuration;
            this.taglibFactory = taglibFactory;
        }

        @Override
        public freemarker.template.Configuration getConfiguration() {
            return configuration;
        }

        @Override
        public TaglibFactory getTaglibFactory() {
            return taglibFactory;
        }
    }
}

Add the following to your pom.xml:

    
        org.springframework
        spring-webmvc
    
    
        javax.servlet.jsp
        jsp-api
        2.0
    

Then you can load in your template:

<#assign s=JspTaglibs["/META-INF/spring.tld"] />

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