Velocity Simple to use

I. Velocity SCRIPT Syntax Summary

1. Variables

(1) Definition of variable:

#set ($name = "Hello") Description: The variable in velocity is weakly typed.

When using the #set instruction, the literal string enclosed in double quotation marks is parsed and re-interpreted as follows: #set ($directoryRoot = "www")

#set ($templateName = "INDEX.VM")

#set ($template = "$directoryRoot/$templateName")

$template

The output will be: WWW/INDEX.VM

Note: It is not a problem to use a currency identifier such as $2.5 in velocity, because the variables in velocity always start with a letter in uppercase or lowercase.

(2) The wording of the variable specification

${name} can also be written as: $name. Promote the use of the preceding wording.

For example, you want to dynamically organize a string by using a variable $vice.

Jack is a $vicemaniac.

The original variable is $vice now becomes $vicemaniac, so veloctiy don't know what you want. Therefore, it should be written in a canonical format: Jack is a ${vice}maniac

Velocity now knows that the variable is $vice rather than $vicemaniac.

Note: You cannot add {} When referencing a property

(3) Assignment of variables:

$name = "Hello"

The left side of the assignment must be a variable or a property reference. The right side can be one of the following six types:

Variable references, literal strings, property references, method references, literal numbers, array lists.

The following example shows each of these types:

#set ($monkey = $bill) # variable reference

#set ($monkey. Friend = "Monica") # # String

#set ($monkey. Blame = $whitehouse. Leak) # # Property Reference

#set ($monkey. Plan = $spindoctor. Weave ($web)) # # Method Reference

#set ($monkey. Number = 123) # #number

#set ($monkey. Say = ["not", $my, "Fault"]) # # ArrayList

Note: ① if the right value in the above example is null, then the lvalue is not assigned, which means that the previous value is preserved. Variables that are not defined in the ②velocity template are considered to be a string. For example:

#set ($foo = "gibbous")

$moon = $foo

The output is:

$moon = gibbous

Reference is not interpreted as an instance variable of an object in the ③velocity template. For example: $foo. Name will be interpreted as the GetName () method of the Foo object, not the name instance variable of the Foo object. For example: $foo. Getbar () is equivalent to $foo. Bar;

$data. GetUser ("Jon") is equivalent to $data. User ("Jon");

Data.getrequest (). getServerName () is equivalent to

$data. Request.servername is equivalent to ${data. Request.servername}

2. Cycle

#foreach ($element in $list)

This is $element.

$velocityCount

#end

Example:

#set ($list = ["Pine", "oak", "maple"])

#foreach ($element in $list)

$velocityCount

This is $element .<br>

#end

The result of the output is:

1 This is pine.

2 This is oak.

3 This is maple.

A value in the $list of each loop is assigned to the $element variable.

$list can be a vector, Hashtable, or array. The value assigned to $element is a Java object and can be referenced by a variable. For example: if $element T is a Java product class, and the name of the product can be obtained by calling his GetName () method.

#foreach ($key in $list. KeySet ())

Key: $key, Value: $list. Get ($key) <br>

#end

Tip: Velocity is case sensitive.

Velocity also provides a way to get the number of cycles, $velocityCount the name of the variable is the default name of velocity.

Example:

First example:

#foreach ($foo in [1..5])

$foo

#end

Second Example:

#foreach ($bar in [2..-2])

$bar

#end

Third example:

#set ($arr = [0..1])

#foreach ($i in $arr)

$i #end

The output of the above three examples is:

First example:

1 2 3) 4 5

Second Example:

2 1 0-1-2

Third example:

0 1

3. Conditional statements

#if (condition)

#elseif (condition)

#else

#end 4. Nesting of statements

#foreach ($element in $list) # # inner foreach inner loop #foreach ($element in $list) the is $element. $velocityCount <br>inner<br> #end # # inner foreach Inner Loop End # # outer foreach this is $element. $velocityCount <br>outer<br> #end

Statements can also be nested in other statements, such as the # if "#else" #end等.

5. Notes

(1) Single-line comment:

# # This is a single line comment.

(2) Multi-line Comment:

#*

Thus begins a multi-line comment. Online visitors won ' t see this text because the Velocity templating Engine would ignore it.

*#

(3) Document format:

#**

This is a VTL comment block and

May is used to store such information

As the document author and Versioning

Information:

@version 1.1

@author Xiao

*#

6. Relational and logical operators

Velocity also has a logical and, or, and not operator.

Such as

# # Example for and

#if ($foo && $bar)

<strong> this and that</strong>

#end

Examples where the # if () directive is true only when the $foo and $bar are true. If $foo is false, the expression is also false, and $bar will not be evaluated. If the $foo is true, the Velocity template engine will continue to check the value of $bar, and if the $bar is true, the entire expression is true. and output this and that. If the $bar is false, there will be no output because the entire expression is false.

Macros in 7.Velocity

A macro in velocity can be understood as a function.

① Definition of macros

#macro (macro name $ parameter 1 $ parameter 2 ...)

Statement body (i.e. function body)

#end

② calls to macros

#宏的名称 ($ parameter 1 $ parameter 2 ...)

Description: The parameters are separated by a space.

8. #stop

It is helpful to stop executing the template engine and return it and apply it to debug.

9. #include与 #parse

#include和 #parse's role is to introduce local files, for security reasons, the local files that are introduced can only be in the Template_root directory.

Difference:

(1) Unlike # include, #parse只能指定单个对象. And # include can have multiple

If you need to introduce multiple files, you can separate the lines with commas:

#include ("One.gif", "Two.txt", "three.htm")

The file name can be in parentheses, but more often it uses variables:

#include ("Greetings.txt", $seasonalstock)

(2) #include被引入文件的内容将不会通过模板引擎解析;

The #parse introduction of the file content velocity will parse the velocity syntax and hand it over to the template, meaning quite similar to copy the introduced file into the file. #parse是可以递归调用的, for example: If DOFOO.VM contains the following line:

Count down.<br>

#set ($count = 8)

#parse ("PARSEFOO.VM") <br>all done with dofoo.vm!

So in the PARSEFOO.VM template, you can include the following vtl:

$count

#set ($count = $count-1)

#if ($count > 0) <br>

#parse ("PARSEFOO.VM")

#else

<br>all Done with parsefoo.vm!

#end的显示结果为:

Count down.

8

7

6

5

4

3

2

1

All do with parsefoo.vm!

All do with dofoo.vm!

Note: variable sharing issues when using #parse in a VM to nest another VM. Such as:

->A.VM nested in B.VM;

The variable $param is defined in->A.VM;

->B.VM can be used directly in the $param without any restrictions.