Spring boot and Thymeleaf - Hot swap templates and resources once again

Question

I tried all tips and tricks that I found here and in docs, but still no luck. I have Spring webapp with Thymeleaf. Resources and templates are not reloaded when I call update in IDEA (it says nothing to reload). I can then press ctrl+f5 in a browser like crazy, changes are just not there.

Everything is configured in one Java class like this:

@EnableWebMvc
public class MvcConfig extends WebMvcConfigurerAdapter implements ApplicationContextAware {

My folder structure now looks like this, but I also tried to put the resources without "static" folder or to webapp/resources.

ResourceHandlerRegistry:

@Override
public void addResourceHandlers(final ResourceHandlerRegistry registry) {
    super.addResourceHandlers(registry);
    registry.addResourceHandler("/img/**").addResourceLocations("classpath:/static/img/");
    registry.addResourceHandler("/css/**").addResourceLocations("classpath:/static/css/");
    registry.addResourceHandler("/js/**").addResourceLocations("classpath:/static/js/");
}

I specified cache=false in both application.properties:

spring.thymeleaf.cache=false

and in mentioned MvcConfig class:

@Bean
public SpringResourceTemplateResolver templateResolver() {
    SpringResourceTemplateResolver templateResolver = new SpringResourceTemplateResolver();
    templateResolver.setApplicationContext(this.applicationContext);
    templateResolver.setPrefix("/WEB-INF/templates/");
    templateResolver.setSuffix(".html");
    templateResolver.setTemplateMode(TemplateMode.HTML);
    templateResolver.setCacheable(false);
    return templateResolver;
}

According to some answers on SO i added dependency for devtools:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <version>1.4.1.RELEASE</version>
    <optional>true</optional>
</dependency>

Still not working. Some said to add maven boot plugin with addResources=true, so I did:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <version>1.4.1.RELEASE</version>
    <configuration>
        <addResources>true</addResources>
    </configuration>
</plugin>

My Idea is set properly I guess, because when I call update, my Java classes are reloaded immediately. Only resources and html files are not, I must restart server for it. Actualy *.html files are not so big a deal, but to restart server after every small css and js change is slowing me down a lot, and as I lost almost 15 hours figuring out what is wrong, it started to be really frustrating.

Any help will be greatly appreciated.

Answer 1

The simplest solution is to configure Spring's Thymeleaf template source to load from the filesystem, rather than the classpath.

This is a super-simple -- esentially a one-liner in config -- but seems little-known on the Internet. Credit to @JianrongChen's for posting it in his comment.

application.properties

# Thymeleaf templates from filesystem, not cached
#
spring.thymeleaf.cache=false
spring.thymeleaf.prefix=file:src/main/resources/templates/

# static content from filesystem first, too
#
spring.web.resources.static-locations[0]=file:src/main/resources/static/
spring.web.resources.static-locations[1]=classpath:/static

References:

• https://docs.spring.io/spring-boot/docs/current/reference/html/application-properties.html#application-properties.templating.spring.thymeleaf.prefix

Answer 2

@Luke my solution was quite simple:

To have HTML / CSS / JS reloading automatically in Spring Thymeleaf can be simple and bug free, have only tested in IntelliJ.

Add this to maven, use ${spring.version} var or replace by your version:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <version>${spring.version}</version>
    <optional>true</optional>
    <scope>runtime</scope>
</dependency>

Add to the header of the html:

<script src="http://localhost:35729/livereload.js"></script>

When using IntelliJ:

Answer 3

Here are my settings with IntelliJ IDEA (2018.3), it's reload HTML after the changes are saved:

1. In application.properties:

   spring.resources.static-locations = classpath:/resources/static
   spring.resources.cache.period = 0
   

2. In pom.xml, set <addResources>true</addResources>

   <plugin>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-maven-plugin</artifactId>
       <configuration>
           <addResources>true</addResources>
       </configuration>
   </plugin>
   

3. Menu Run => Edit Configurations (IntelliJ IDEA)

On frame deactivation: Update resources

Answer 4

I have spent some time on it and finally here I'll explain how I got it working. Googling around you may find several info:

• Spring Boot hot swap
• SO - Spring Boot + Jetty & hot deployment
• SO - Netbeans 8 won't reload static Thymeleaf files

My inital approach was to disable caching and add Spring dev tools:

Spring boot application.properties

spring.thymeleaf.cache=false
spring.thymeleaf.mode=LEGACYHTML5
spring.thymeleaf.prefix=/templates/

pom.xml

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-devtools</artifactId>
        <optional>true</optional>
    </dependency>

Using the snippet above however is not enough since the hot swap is done only when making the project (CTRL + F9 in Intellij Idea). This is due to the fact that the default template resolver is classpath based and that's the reason a recompilation is necessary.

---

A working solution is to override the defaultTemplateResolver by using a file system based resolver:

application.properties

spring.thymeleaf.cache=false
spring.thymeleaf.mode=LEGACYHTML5
spring.thymeleaf.templates_root=src/main/resources/templates/

Application class

@SpringBootApplication
public class MyApplication {

    @Autowired
    private ThymeleafProperties properties;

    @Value("${spring.thymeleaf.templates_root:}")
    private String templatesRoot;

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

    @Bean
    public ITemplateResolver defaultTemplateResolver() {
        FileTemplateResolver resolver = new FileTemplateResolver();
        resolver.setSuffix(properties.getSuffix());
        resolver.setPrefix(templatesRoot);
        resolver.setTemplateMode(properties.getMode());
        resolver.setCacheable(properties.isCache());
        return resolver;
    }
}

I find this solution optimal since it allow you to externalize the configuration and use different profiles (dev, prod, etc..) while having the benefit of reloading the changes by just pressing F5 :)

Answer 5

Okay, so I found answer to my specific case. Problem was not at all in my app or it's config (well.. probably). Instead of using Tomcat 8.5.5 I switched back to Tomcat 7. Everything now works properly. Does somebody know why?