Why doesnt work a backslash in front of a reference - junit

Question

I wrote a simple junit test. I want to test if I can write a java escaped backslash in front of a reference. This test fails and I dont know why.
Error Message: org.junit.ComparisonFailure: expected:<[\London]> but was:<[$branch]>
public class VelocityBackslashTest {
#Test
public void testVelocityBackslash() {
String inString = "\\$branch";
Velocity.init();
VelocityContext context = new VelocityContext();
context.put("branch", "London");
StringWriter writer = new StringWriter();
Velocity.evaluate(context, writer, "test_1", inString);
assertEquals("\\London", writer.toString());
}
}
If I do the same test but reading the template from a file. The result is positiv.
public class VelocityBackslashFileTest {
#Test
public void testVelocityBackslash() {
Properties p = new Properties();
p.setProperty("resource.loader", "classpath");
p.setProperty("classpath.resource.loader.class",
ClasspathResourceLoader.class.getName());
Velocity.init(p);
Template template =
Velocity.getTemplate("velocity/test_template.vm");
VelocityContext context = new VelocityContext();
context.put("branch", "London");
StringWriter writer = new StringWriter();
template.merge(context, writer);
assertEquals("\\London", writer.toString());
}
}
test_template.vm:
\\$branch

Answer 1

This is happening because of java.lang.String's use of \ as an escape character.
When you write
String inString = "\\$branch";
Java interprets the String literal \\ as an escaped backslash, so what is actually getting passed to Velocity is a single \ followed by $branch.
Velocity also uses \ as the escape character, so it interprets its input (\$branch) as a directive to escape the $ symbol. In other words, don't use it as Velocity markup simply print the literal $. Once this has happened then of course there is no attempt to resolve branch as a reference hence it is output as a literal.
To print \\ in front of a resolved Velocity reference, the Java String would need to pass 2 \ characters to Velocity, which would be done like this:
String inString = "\\\\$branch";