Thymeleaf Tutorial: Chapter 7. Conditional Execution

Table of contents

7 Conditional execution

7.1 Simple conditions: “if” (if) and “unless” (if not)

Sometimes you need a template fragment to appear only as a result of a certain condition.

For example, imagine that we want to show in the product table a column with the number of comments that exist for each product, and if there are any comments, a link to the comment page.

To do this, use attribute th: the if :

NAME
PRICE
IN STOCK
COMMENTS
Onions
2.41
yes
2 comment/s
      view

There are so many things here, so let's focus on the important line:

view

This code will create a link to the comments page (with URL / product / comments) with the prodId parameter set to the product identifier, but only if the product has any comments.

Let's look at the resulting markup:

NAME
PRICE
IN STOCK
COMMENTS
Fresh Sweet Basil
4.99
yes
0 comment/s
    
Italian Tomato
1.25
no
2 comment/s
      view
Yellow Bell Pepper
2.50
yes
0 comment/s
    
Old Cheddar
18.75
yes
1 comment/s
      view

Excellent! This is exactly what we wanted.

Note that the th: if attribute will not only evaluate logical conditions. Its capabilities are slightly higher than this, and it will evaluate the specified expression as true, following these rules:

If the value is not null :

• If the value is boolean and true
• If the value is a number and nonzero
• If the value is a character and non-zero
• If the value is String and is not false, off or no
• If the value is not a boolean, number, character or String

If the value is null , th: if will be set to false .

In addition, th: if has an inverse attribute, th: unless, which we could use in the previous example instead of using not (negation) inside the OGNL expression:

view

7.2 Switch statements

There is also a way to conditionally display content using the equivalent switch structure in Java: the th: switch / th: case attribute set .

User is an administrator
User is a manager

Note that as soon as one th: case attribute evaluates to true, every other th: case attribute evaluates to false in the same switch context.

The default parameter is specified as: th: case = "*" :

User is an administrator
User is a manager
User is some other thing