velocity的基础语法

简介

velocity可以动态创建并保存静态页面，这样的话可以避免与数据库交互，实现页面的静态化，所以执行效率要比jsp高很多

其和jsp以及freemark都是作为前台的显示层其各自优缺点如下：

jsp是大家最熟悉的技术 
优点： 
1、功能强大，可以写java代码 
2、支持jsp标签（jsp tag） 
3、支持表达式语言（el） 
4、官方标准，用户群广，丰富的第三方jsp标签库 
5、性能良好。jsp编译成class文件执行，有很好的性能表现 
缺点： 
jsp没有明显缺点，非要挑点骨头那就是，由于可以编写java代码，如使用不当容易破坏mvc结构。 

velocity是较早出现的用于代替jsp的模板语言 
优点： 
1、不能编写java代码，可以实现严格的mvc分离 
2、性能良好，据说比jsp性能还要好些 
3、使用表达式语言，据说jsp的表达式语言就是学velocity的 
缺点： 
1、不是官方标准 
2、用户群体和第三方标签库没有jsp多。 
3、对jsp标签支持不够好 

freemarker 
优点： 
1、不能编写java代码，可以实现严格的mvc分离 
2、性能非常不错 
3、对jsp标签支持良好 
4、内置大量常用功能，使用非常方便 
5、宏定义（类似jsp标签）非常方便 
6、使用表达式语言 
缺点： 
1、不是官方标准 
2、用户群体和第三方标签库没有jsp多 

使用过程图

使用velocity

try {

			Velocity.init("src/velocity.perties");//velocity的配置属性文件
			VelocityContext context = new VelocityContext();
			context.put("person", new Person());//将变量放入velocity容器
			context.put("dataTool", new DateTool());//扩展veloctiy功能，因为velocity模版可以调用对象的方法
			Template template = Velocity.getTemplate("temp.html");//读取velocity模板也可以是.vm文件
			File saveFile = new File("html/temp.html");//输出并存放静态文件
			if (!saveFile.getParentFile().exists()) {
				saveFile.getParentFile().mkdirs();
			}
			FileOutputStream outputStream = new FileOutputStream(saveFile);
			OutputStreamWriter oWriter = new OutputStreamWriter(outputStream,
					"UTF-8");
			template.merge(context, oWriter);
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}

velocity的属性文件

位于org.apache.velocity.runtime.default包下面的velocity.properties属性文件里

# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.    

# ----------------------------------------------------------------------------
# R U N T I M E  L O G
# ----------------------------------------------------------------------------

# ----------------------------------------------------------------------------
#  default LogChute to use: default: AvalonLogChute, Log4JLogChute, CommonsLogLogChute, ServletLogChute, JdkLogChute
# ----------------------------------------------------------------------------

runtime.log.logsystem.class = org.apache.velocity.runtime.log.AvalonLogChute,org.apache.velocity.runtime.log.Log4JLogChute,org.apache.velocity.runtime.log.CommonsLogLogChute,org.apache.velocity.runtime.log.ServletLogChute,org.apache.velocity.runtime.log.JdkLogChute

# ---------------------------------------------------------------------------
# This is the location of the Velocity Runtime log.
# ----------------------------------------------------------------------------

runtime.log = velocity.log

# ----------------------------------------------------------------------------
# This controls whether invalid references are logged.
# ----------------------------------------------------------------------------

runtime.log.invalid.references = true

# ----------------------------------------------------------------------------
# T E M P L A T E  E N C O D I N G
# ----------------------------------------------------------------------------

input.encoding=ISO-8859-1
output.encoding=ISO-8859-1

# ----------------------------------------------------------------------------
# F O R E A C H  P R O P E R T I E S
# ----------------------------------------------------------------------------
# These properties control how the counter is accessed in the #foreach
# directive. By default the reference $velocityCount and $velocityHasNext
# will be available in the body of the #foreach directive.
# The default starting value for $velocityCount is 1.
# ----------------------------------------------------------------------------

directive.foreach.counter.name = velocityCount
directive.foreach.counter.initial.value = 1
directive.foreach.maxloops = -1

directive.foreach.iterator.name = velocityHasNext

# ----------------------------------------------------------------------------
# S E T  P R O P E R T I E S
# ----------------------------------------------------------------------------
# These properties control the behavior of #set.
# For compatibility, the default behavior is to disallow setting a reference
# to null.  This default may be changed in a future version.
# ----------------------------------------------------------------------------

directive.set.null.allowed = false

# ----------------------------------------------------------------------------
# I F  P R O P E R T I E S
# ----------------------------------------------------------------------------
# These properties control the behavior of #if
# Default behavior is to check return value of toString() and treat an object
# with toString() that returns null as null. If all objects have toString()
# methods that never return null, this check is unnecessary and can be disabled
# to gain performance. In Velocity 1.5, no such null check was performed.
directive.if.tostring.nullcheck = true

# ----------------------------------------------------------------------------
# I N C L U D E  P R O P E R T I E S
# ----------------------------------------------------------------------------
# These are the properties that governed the way #include'd content
# is governed.
# ----------------------------------------------------------------------------

directive.include.output.errormsg.start = 

# ----------------------------------------------------------------------------
# P A R S E  P R O P E R T I E S
# ----------------------------------------------------------------------------

directive.parse.max.depth = 10

# ----------------------------------------------------------------------------
# S C O P E  P R O P E R T I E S
# ----------------------------------------------------------------------------
# These are the properties that govern whether or not a Scope object
# is automatically provided for each of the given scopes to serve as a
# scope-safe reference namespace and "label" for #break calls. The default
# for most of these is false.  Note that  should be replaced by
# name of macros that take bodies for which you want to suppress the scope.
# ----------------------------------------------------------------------------
# template.provide.scope.control = false
# evaluate.provide.scope.control = false
foreach.provide.scope.control = true
# macro.provide.scope.control = false
# define.provide.scope.control = false
# .provide.scope.control = false

# ----------------------------------------------------------------------------
# T E M P L A T E  L O A D E R S
# ----------------------------------------------------------------------------
#
#
# ----------------------------------------------------------------------------

resource.loader = file

file.resource.loader.description = Velocity File Resource Loader
file.resource.loader.class = org.apache.velocity.runtime.resource.loader.FileResourceLoader
file.resource.loader.path = .
file.resource.loader.cache = false
file.resource.loader.modificationCheckInterval = 2

string.resource.loader.description = Velocity String Resource Loader
string.resource.loader.class = org.apache.velocity.runtime.resource.loader.StringResourceLoader

# ----------------------------------------------------------------------------
# VELOCIMACRO PROPERTIES
# ----------------------------------------------------------------------------
# global : name of default global library.  It is expected to be in the regular
# template path.  You may remove it (either the file or this property) if
# you wish with no harm.
# ----------------------------------------------------------------------------
# velocimacro.library = VM_global_library.vm

velocimacro.permissions.allow.inline = true
velocimacro.permissions.allow.inline.to.replace.global = false
velocimacro.permissions.allow.inline.local.scope = false

velocimacro.context.localscope = false
velocimacro.max.depth = 20

# ----------------------------------------------------------------------------
# VELOCIMACRO STRICT MODE
# ----------------------------------------------------------------------------
# if true, will throw an exception for incorrect number 
# of arguments.  false by default (for backwards compatibility)
# but this option will eventually be removed and will always
# act as if true
# ----------------------------------------------------------------------------
velocimacro.arguments.strict = false

# ----------------------------------------------------------------------------
# VELOCIMACRO BODY REFERENCE 
# ----------------------------------------------------------------------------
# Defines name of the reference that can be used to render the AST block passed to
# block macro call as an argument inside a macro.
# ----------------------------------------------------------------------------
velocimacro.body.reference=bodyContent

# ----------------------------------------------------------------------------
# STRICT REFERENCE MODE
# ----------------------------------------------------------------------------
# if true, will throw a MethodInvocationException for references
# that are not defined in the context, or have not been defined
# with a #set directive. This setting will also throw an exception
# if an attempt is made to call a non-existing property on an object
# or if the object is null.  When this property is true then property
# 'directive.set.null.allowed' is also set to true.
# ----------------------------------------------------------------------------
runtime.references.strict = false

# ----------------------------------------------------------------------------
# INTERPOLATION
# ----------------------------------------------------------------------------
# turn off and on interpolation of references and directives in string
# literals.  ON by default :)
# ----------------------------------------------------------------------------
runtime.interpolate.string.literals = true


# ----------------------------------------------------------------------------
# RESOURCE MANAGEMENT
# ----------------------------------------------------------------------------
# Allows alternative ResourceManager and ResourceCache implementations
# to be plugged in.
# ----------------------------------------------------------------------------
resource.manager.class = org.apache.velocity.runtime.resource.ResourceManagerImpl
resource.manager.cache.class = org.apache.velocity.runtime.resource.ResourceCacheImpl

# ----------------------------------------------------------------------------
# PARSER POOL
# ----------------------------------------------------------------------------
# Selects a custom factory class for the parser pool.  Must implement
# ParserPool.  parser.pool.size is used by the default implementation
# ParserPoolImpl
# ----------------------------------------------------------------------------

parser.pool.class = org.apache.velocity.runtime.ParserPoolImpl
parser.pool.size = 20


# ----------------------------------------------------------------------------
# EVENT HANDLER
# ----------------------------------------------------------------------------
# Allows alternative event handlers to be plugged in.  Note that each
# class property is actually a comma-separated list of classes (which will
# be called in order).
# ----------------------------------------------------------------------------
# eventhandler.referenceinsertion.class =
# eventhandler.nullset.class =
# eventhandler.methodexception.class =
# eventhandler.include.class =


# ----------------------------------------------------------------------------
# EVALUATE
# ----------------------------------------------------------------------------
# Evaluate VTL dynamically in template.  Select a class for the Context, if
# you want all #set calls within it to be locally scoped.  This feature is
# deprecated; please use $evaluate to hold local references instead.
# ----------------------------------------------------------------------------

#directive.evaluate.context.class = org.apache.velocity.VelocityContext


# ----------------------------------------------------------------------------
# PLUGGABLE INTROSPECTOR
# ----------------------------------------------------------------------------
# Allows alternative introspection and all that can of worms brings.
# ----------------------------------------------------------------------------

runtime.introspector.uberspect = org.apache.velocity.util.introspection.UberspectImpl


# ----------------------------------------------------------------------------
# SECURE INTROSPECTOR
# ----------------------------------------------------------------------------
# If selected, prohibits methods in certain classes and packages from being 
# accessed.
# ----------------------------------------------------------------------------

introspector.restrict.packages = java.lang.reflect

# The two most dangerous classes

introspector.restrict.classes = java.lang.Class
introspector.restrict.classes = java.lang.ClassLoader
                
# Restrict these for extra safety

introspector.restrict.classes = java.lang.Compiler
introspector.restrict.classes = java.lang.InheritableThreadLocal
introspector.restrict.classes = java.lang.Package
introspector.restrict.classes = java.lang.Process
introspector.restrict.classes = java.lang.Runtime
introspector.restrict.classes = java.lang.RuntimePermission
introspector.restrict.classes = java.lang.SecurityManager
introspector.restrict.classes = java.lang.System
introspector.restrict.classes = java.lang.Thread
introspector.restrict.classes = java.lang.ThreadGroup
introspector.restrict.classes = java.lang.ThreadLocal

语法demo

 

 
##1. 单行注释
 
#*2. 多行注释
 
多行注释*#
 
##3. 变量赋值
 
#set($var="Velocity")
 
##4. 变量 第一个字符必须为字母
 
 4.The var is: $var
 
##5.字符串拼接
 
#set ( $size="Big" )
 
#set ( $name="Ben" )
 
#set ( $clock="$size$name")
 
5.字符串拼接: $clock 
 
##6. 单双引号
 
 6. 双引号时： 
 
#set ( $clock="$size$name")
 
$clock
 
 单引号时： 
 
#set ($clock='$size$name')
 
$clock
 
##7. {}
 
7. 没用{}:this is a $varfile.
 
用{}: this is a ${var}file.
 
##8. ! ?
 
#set($var=$null)
 
8. 没用!: $null
 
 用!: $!null 
 
##9. \ 转义
 
#set( $var = "Velocity" )
 
9. \$var变为: $var
 
\\\$var变为: \$var
 
\\\\\$var变为: \\$var
 
\\\\\\\$var变为: \\\$var
 
##10. if else
 
10. if else例子：
 
#if( $var )
 
run if!
 
#else
 
run else!
 
#end
 
#*11. #set( LHS = RHS )
 
LHS可以是变量引用或属性引用
 
RHS可以是引用、字符串、数字、ArrayList或Map *#
 
##set($var.list=["Not", "wrong", "fault"])
 
##set($var.Map=["banana": "good", "roast beef":"bad"])
 
##12. #foreach
 
##arraylist table...
 
12. foreach列表:
 
#set($criteria=["java", "c", "php"])
 
#foreach($lang in $criteria)
 
$velocityCount
 
$lang
 
#end
 
## num scope
 
数字范围：
 
#foreach( $num in [1..5] )
 
$num
 
#end
 
##13. #macro宏命令
 
13. macro 无参数：
 
#macro( macroo )
 
$var
 
#end
 
##调用
 

 
#macroo()
 
#macroo()
 

 
13. macro 有参数：
 
##参数为：$color 和$somelist
 
#macro( macroname $color $somelist )
 
#foreach( $something in $somelist )
 
$something
 
#end
 
#end
 
##调用
 
#set( $greatlakes = ["Superior","Michigan","Huron","Erie","Ontario"] )
 
#set( $color = "blue" )
 

 
#macroname( $color $greatlakes ) ##调用模板tablerows
 

 
13. macro嵌套 参数以by name形式传递
 
##声明
 
#macro( inner $foo )
 
inner : $foo
 
#end
 
#macro( outer $foo )
 
#set($bar = "outerlala")
 
outer : $foo
 
#end
 
##调用
 
#set($bar = 'calltimelala')
 
#outer( "#inner($bar)" )
 
## include 导入的文件内容不会被模板引擎解析。
 
## parse 许导入一个包含VTL的本地文件，并由模板引擎进行解析。
 
## #stop 停止模板引擎的执行并返回。这在Debug时很有用。