Small Talks/2015/May/New Features of ZK 8.0.0

Author
Timothy Clare, Potix Corporation

Date
May, 2015

Version
ZK 8.0.0 RC

Introduction

The ZK team is proud to announce the release of ZK 8!

ZK 8's main focus was on improving

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Support Expression Language 3 (EL3)

introduce the new generation expression language of Java EE 7 – Expression Language 3 (EL 3) into ZK 8 so we can do more complicated and more powerful things with the newer expression language. There are many new features in EL 3 such as new operators, lambda expressions and collection operations. For more information on EL3 please take a look at the specification, JSR-341.

MENTION WORKS FOR JDK5

Lambda Expressions

Each converter is implemented with the capability to interpret lambda expressions defined in zul. The following shows an example of a textbox who's value and onOK command are both driven by lambdas.

<textbox value="@load((x -> (x * 100) / 2.54)(vm.value))" 
    onOK="@command('click', key=((x -> (x * 2.54) / 100)(self.value)))" />

The syntax used is same as ones in Java SE 8 and behaves like an anonymous function which is discarded after evaluated. We can name a lambda and evaluate indirectly.

Let us take the lambda expression (x -> (x * 100) / 2.54). In this case it will create an anonymous function which takes a value, multiplies it by 100 and divides the result by 2.54. This function is then applied to vm.value, where vm stands for our viewmodel.

To simplify this let us write some psuedo code for demonstration purposes.

myFunction = x -> (x * 100) / 2.54 //assign a lambda to myFunction temporarily
myFunction(vm.value) //execute myFunction passing vm.value as the parameter

While the above is just pseudo code to better help you understand the functionality it does demonstrate naming of lambdas, which is also possible. The following section outlines how to do this using two new operators.

New Operators

String Concatenation

String concatenation has been introduced to make it easy to construct strings within EL expressions. The following code snippet demonstrates how to do so.

<label value="@load(('Hi, ' += vm.firstname += ' ' += vm.lastname))" />

Assignment and Semicolons

Both assignment and semicolon operators are now implemented. Below shows an example of both being used.

<label value="@load((incr = x -> x + 1; incr(5)))" />

The assignment operator in this instance assigns a lambda function to incr which takes x, increments by 1 and then returns it.

incr = x -> x + 1

By using the ';' operator it evaluates the left hand side first, thus creating a lambda function incr, as previously discussed. Then evaluates and returns the right hand side. So in the following case:

<label value="@load((incr = x -> x + 1; incr(5)))" />

The value assigned to the label would be 6, as the lambda function is first evaluated and assigned to incr, then the incr(5) call is evaluated leading to a return value of 6.

Collection Operations

In ZK 8 it is now possible to use collection chain operations directly. In the example below we turn vm.names into stream() and then can create a pipeline of commands.

<listbox model="@load((vm.names.stream()
                               .filter(x -> x.contains(vm.filter))
                               .toList()))">

In addition to pipelines ZK 8's EL 3 supports easy collection construction using brackets ([ ]). The following example demonstrates this.

<label value="@load(([1, 2, 3, 4].stream().sum()))" />

Static Field and Method References

A static field or static method of a Java class can be referenced with the syntax Classname.Field, such as

	
<label value="@load((Math.sqrt(16)))" />

Please note that java.lang.* is imported by default.

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