通过压缩组件，可以显著减少HTTP请求和响应事件。这也是减小页面大小最简单的技术，但也是效果最明显的。
压缩JS，CSS代码有几种常用插件，YUI Compressor是个不错的选择。通过maven的YUI Compressor plugin可以方便的压缩项目中的前端代码。最简单便是将所有的文件一一压缩，看下pom.xml的配置：
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>KUI_demo</groupId>
<artifactId>KUI_demo</artifactId>
<version>1.0</version>
<packaging>jar</packaging>
<build>
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>yuicompressor-maven-plugin</artifactId>
<version>1.3.0</version>
<executions>
<execution>
<!-- YUI Compressor has two goals: compress and jslint -->
<goals>
<goal>compress</goal>
</goals>
</execution>
</executions>
<configuration>
<failOnWarning>false</failOnWarning>
<!-- Break contiguous output at this column number. -->
<!-- If this is zero, you will get line breaks after every line in the aggregated file. -->
<linebreakpos>-1</linebreakpos>
<!-- Set your own suffix. [default: "-min"]-->
<nosuffix>true</nosuffix>
</configuration>
</plugin>
</plugins>
<resources>
<resource>
<directory>${basedir}/webapp</directory>
<includes>
<include>**/*.js</include>
<include>**/*.css</include>
</includes>
</resource>
</resources>
</build>
</project>
更进一步，将所有文件合并到同一个文件，可以减少HTTP请求。由于项目开发阶段并不会压缩所有代码，因此，可以采取通过一个JS引进所有其他文件。后期压缩的时候，将所有代码压缩进该文件。
看看复杂一点的需求：
- 先压缩文件，并排除部分已压缩的文件。
- 合并已压缩文件，并排除部分不需要合并的文件。
- 将压缩好的文件放到指定文件夹。
先看看合并的基本配置：
<project>
...
<build>
<plugins>
...
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>yuicompressor-maven-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>compress</goal>
</goals>
</execution>
</executions>
<configuration>
<nosuffix>true</nosuffix>
<aggregations>
<aggregation>
<!-- remove files after aggregation (default: false)
<removeIncluded>true</removeIncluded>
-->
<!-- insert new line after each concatenation (default: false) -->
<insertNewLine>true</insertNewLine>
<output>${project.build.directory}/${project.build.finalName}/static/all.js</output>
<!-- files to include, path relative to output's directory or absolute path-->
<!--inputDir>base directory for non absolute includes, default to parent dir of output</inputDir-->
<includes>
<include>${basedir}/src/licenses/license.js</include>
<include>**/*.js</include>
</includes>
<!-- files to exclude, path relative to output's directory
<excludes>
<exclude>**/*.pack.js</exclude>
<exclude>**/compressed.css</exclude>
</excludes>
-->
</aggregation>
</aggregations>
</configuration>
</plugin>
...
</plugins>
</build>
...
</project>
注意aggregation的inputDir非常重要，它默认为outputDir的上一层。并且aggregation的动作是在yuicompression之后的。因此，上面的配置实际上是先将代码压缩到${project.build.directory}/${project.build.finalName}目录下再进行aggregation。
<configuration>
<!-- exclude file witch not need to compress -->
<excludes>
<exclude>**/*.min.js</exclude>
<exclude>**/KUI.js</exclude>
</excludes>
<includes>
<include>**/*.js</include>
<include>**/*.css</include>
</includes>
<linebreakpos>-1</linebreakpos>
<nosuffix>false</nosuffix>
<suffix>.min</suffix>
<preProcessAggregates>false</preProcessAggregates>
<preserveAllSemicolons>true</preserveAllSemicolons>
<failOnWarning>false</failOnWarning>
<aggregations>
<!-- JS concatenation -->
<aggregation>
<inputDir>${project.build.directory}</inputDir>
<!-- Insert a new line after each concatenation. -->
<insertNewLine>true</insertNewLine>
<removeIncluded>false</removeIncluded>
<!-- Pathname of final output. -->
<output>${basedir}/webapp/KUI.min.js</output>
<!-- Files to include, path relative to output directory OR absolute path -->
<includes>
<inlcude>**/*.min.js</inlcude>
</includes>
<excludes>
<exclude>**/KUI.js</exclude>
<exclude>**/KUI.min.js</exclude>
</excludes>
</aggregation>
<!-- CSS concatenation -->
<aggregation>
<inputDir>${project.build.directory}</inputDir>
<!-- Pathname of final output. -->
<output>${basedir}/webapp/content.min.css</output>
<!-- Files to include, path relative to output directory OR absolute path -->
<includes>
<include>**/*.min.css</include>
</includes>
</aggregation>
<excludes>
<exclude>**/content.min.css</exclude>
</excludes>
</aggregations>
</configuration>
还有一点要注意，如果对象的属性名为Javascript的保留字，并且没有用引号引住属性名，那么在压缩的时候会抛出错误。
var test = {
long : “test” // throw error when compress
}
var test = {
“long” : “test” // correct.
}