Create a data-model

In simple cases you can build data-models using java.lang and java.util classes and custom JavaBeans:

• Use java.lang.String for strings.

• Use java.lang.Number subclasses for numbers.

• Use java.lang.Boolean for boolean values.

• Use java.util.Date and its subclasses for date/time values

• Use java.util.List or Java arrays for sequences.

• Use java.util.Map with String keys for hashes.

• Use your custom bean class for hashes where the items correspond to the bean properties. For example the price property (getPrice()) of product can be get as product.price. (The actions of the beans can be exposed as well; see much later here)

For example, let's build the data-model of the first example of the Template Author's Guide. For convenience, here it is again:

(root)
  |
  +- user = "Big Joe"
  |
  +- latestProduct
      |
      +- url = "projects.html"
      |
      +- name = "green mouse"

This Java code fragment that builds this data-model:

// Create the root hash. We use a Map here, but it could be a JavaBean too.
Map<String, Object> root = new HashMap<>();

// Put string "user" into the root
root.put("user", "Big Joe");

// Create the "latestProduct" hash. We use a JavaBean here, but it could be a Map too.
Product latest = new Product();
latest.setUrl("projects.html");
latest.setName("green mouse");
// and put it into the root
root.put("latestProduct", latest);

As demonstrated above, for hashes (something that stores other named items) you can use either a Map or any kind of public class that has public getXxx/isXxx methods as prescribed by the JavaBeans specification. Like the above Product class could be something like:

/**
 * Product bean; note that it must be a public class!
 */
public class Product {

    private String url;
    private String name;

    // As per the JavaBeans spec., this defines the "url" bean property
    // It must be public!
    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    // As per the JavaBean spec., this defines the "name" bean property
    // It must be public!
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

Regardless if latestProduct is a Map that contains the "name" and "url" keys, or it's a JavaBean as shown above, in the template you can use ${latestProduct.name}. The root itself need not be a Map either; it could be an object with getUser() and getLastestProduct() methods too.