Thymeleaf at syntax: "#{/}" returns empty if I include ResourceUrlEncodingFilter - spring-mvc

Question

I'm using Thymeleaf.
This template:
<a th:href="#{/}">a</a>
produces this html:
a
This is what I'm expected.
I put ResourceUrlEncodingFilter bean to try ContentVersionStrategy in my WebMvcConfigurerAdapter extended class.
#Bean
public ResourceUrlEncodingFilter resourceUrlEncodingFilter() {
return new ResourceUrlEncodingFilter();
}
The produced html turned to:
a
The value of href is empty.
I hope href is "/" even if I put ResourceUrlEncodingFilter bean.
th:href="#{/a}" turns to href="/a" in both cases.
Did I do something wrong?
Thank you very much.
UPDATE:
This is my build.gradle
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'io.spring.gradle:dependency-management-plugin:0.5.1.RELEASE'
classpath("org.springframework.boot:spring-boot-gradle-plugin:1.2.3.RELEASE")
}
}
apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'spring-boot'
apply plugin: 'io.spring.dependency-management'
version = '1.0'
jar {
manifest {
attributes 'Implementation-Title': 'Gradle Quickstart', 'Implementation-Version': version
}
}
repositories {
mavenCentral()
}
dependencyManagement {
imports {
mavenBom 'io.spring.platform:platform-bom:1.1.2.RELEASE'
}
}
dependencies {
compile('org.webjars:bootstrap:3.3.1')
compile('org.webjars:knockout:3.2.0')
compile('org.webjars:momentjs:2.9.0')
compile('org.webjars:numeral-js:1.5.3-1')
compile('org.webjars:underscorejs:1.7.0-1')
compile('org.webjars:sugar:1.4.1')
compile('org.webjars:jqplot:1.0.8r1250')
compile('org.webjars:jquery-cookie:1.4.1-1')
compile("org.springframework.boot:spring-boot-starter-actuator")
compile("org.springframework.boot:spring-boot-starter-batch")
compile("org.springframework.boot:spring-boot-starter-data-jpa")
compile("org.springframework.boot:spring-boot-starter-security")
compile("org.springframework.boot:spring-boot-starter-web")
compile("org.springframework.boot:spring-boot-starter-tomcat")
compile("org.springframework.boot:spring-boot-starter-thymeleaf")
compile("org.springframework.boot:spring-boot-starter-test")
compile("org.springframework:spring-context-support") // this is for mail
compile('commons-codec:commons-codec')
compile("commons-io:commons-io")
compile('com.google.guava:guava')
compile('org.hibernate:hibernate-validator')
compile("com.sun.mail:javax.mail")
compile('mysql:mysql-connector-java')
compile("org.yaml:snakeyaml")
compile("org.apache.commons:commons-lang3:3.2")
compile('com.amazonaws:aws-java-sdk:1.9.4')
compile('net.sf.supercsv:super-csv:2.2.0')
compile('edu.vt.middleware:vt-password:3.1.2')
}
test {
//systemProperties 'property': 'value'
systemProperties 'spring.profiles.active': 'unittest'
systemProperties 'MAIL_PROP': 'mail.properties'
systemProperties 'user.timezone': 'UTC'
}
uploadArchives {
repositories {
flatDir {
dirs 'repos'
}
}
}

Answer 1

Thanks for this detailed explanation and the repro project!
This is actually a bug: see SPR-13241, to be fixed in Spring 4.1.8 and 4.2.0.

Answer 2

Spring Boot adds "/**" matcher for automatic configurations of static web resources locations.
The locations are /META-INF/resources/, /resources/, /static/ and /public/.
When you put below html in Thymeleaf template,
<a th:href="#{/}">a</a>
Below method in ResourceUrlProvider.java is called because of the matcher and get into for loop:
public final String getForLookupPath(String lookupPath) {
// -- omission --
for(String pattern : matchingPatterns) {
// -- omission --
String pathWithinMapping = getPathMatcher().extractPathWithinPattern(pattern, lookupPath);
String pathMapping = lookupPath.substring(0, lookupPath.indexOf(pathWithinMapping));
// -- omission --
String resolved = chain.resolveUrlPath(pathWithinMapping, handler.getLocations());
if (resolved == null) {
continue;
}
// -- omission --
return pathMapping + resolved;
}
// -- omission --
}
The argument, lookupPath is "/" by the "#{/}", Then:
The pathWithinMapping will be "".
The pathMapping will be "".
The resolved will be "".
So this method returns "" and the value is set to href="".
This is in my opinion, if the pathWithinMapping is "", to continue the for loop seems good. Calling chain.resolveUrlPath seems not good.
Thanks,