使用xsl来动态生成java代码

xsl本身就是一个构型良好的xml，它能够把一个xml文档转换成另外一个xml文档，或者转换成文本文件、html文件等等。这里就是利用xsl来动态的生成我们想要的java文件（从某种角度看，java代码其实也就是一个文本文件），希望能够通过这篇文章，看到xml以及相关的技术所具有的强大能力！

这里首先给一个xml例子，我们将通过一个xsl从该xml文件中抽取有用的信息来生成java代码（实际上是一个javabean）：
以下内容为程序代码:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<bean>
<name>Product</name>
<comments>This bean represents a product that the company
offers to its customers</comments>
<property>
<name>code</name>
<type>int</type>
<comments>the product inventory code</comments>
</property>
<property>
<name>name</name>
<type>String</type>
<comments>the product name</comments>
</property>
<property>
<name>testedOnAnimals</name>
<type>boolean</type>
<comments>the flag that indicates if the product was
tested on animals</comments>
</property>
<property>
<name>availableSince</name>
<type>java.util.Date</type>
<comments>the date when the company started offering this
product to its customers</comments>
</property>
</bean>


下面我就直接给出转换的xsl，如果大家对xsl不是很了解的话，可以先看一些资料，了解之后就会明白了。我在里面稍微做了些注释：
以下内容为程序代码:

<?xml version="1.0"?>
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0"
xmlns:java="http://xml.apache.org/xslt/java"
exclude-result-prefixes="java">

<!--这里就是指定通过这个xsl所转换的结果的类型，是text格式-->
<xsl:output method = "text"/>

<!--xslt使用模版来处理xml中的节点-->
<xsl:template match="bean">

/**
* <xsl:value-of select="comments"/>//这里是获取xml文档中的节点值
* This class has been generated by the XSLT processor from the
metadata
*/
public class <xsl:value-of select="name"/> {

/**
* Creates a new instance of the <xsl:value-of
select="name"/> bean
*/
public <xsl:value-of select="name"/>() {}

<xsl:apply-templates select="property"/>
}
</xsl:template>

<xsl:template match="property">
private <xsl:value-of select="type"/>
<xsl:text> </xsl:text>//输出文本，这里是输出一个空格
<xsl:value-of select="name"/>;
<xsl:variable name="name" select="name"/>//定义xsl中要使用的变量
<xsl:variable name="cname" select="java:Capitalizer.capitalize($name)"/>//这里使用了xslt extensions，它可以允许在xslt中直接引用java中方法，非常方便。
/**
* Sets <xsl:value-of select="comments"/>
* @param <xsl:value-of select="name"/> is <xsl:value-of
select="comments"/>
*/
public void set<xsl:value-of select="$cname"/>(<xsl:value-
of select="type"/> <xsl:text> </xsl:text><xsl:value-
of select="name"/>) {
this.<xsl:value-of select="name"/> = <xsl:value-of
select="name"/>;
}

/**
* Returns <xsl:value-of select="comments"/>
* @return <xsl:value-of select="comments"/>
*/
public <xsl:value-of select="type"/><xsl:text></xsl:text>
<xsl:apply-templates select="type"/><xsl:value-of
select="$cname"/>() {
return <xsl:value-of select="name"/>;
}
</xsl:template>

<xsl:template match="type">
<xsl:variable name="type" select="."/>
<xsl:choose>
<xsl:when test="$type='boolean'">is</xsl:when>
<xsl:otherwise>get</xsl:otherwise>
</xsl:choose>
</xsl:template>

</xsl:stylesheet>


好了，完成以上工作之后，只要在cmd中，输入如下的命令行，就可以获得我们想要的结果了：
java org.apache.xalan.xslt.Process -in xmlSource-xsl stylesheet -out outputfile

这里列出结果：
以下内容为程序代码:

/**
* This bean represents a product that the company offers to its
customers
* This class has been generated by the XSLT processor from the
metadata
*/
public class Product {

/**
* Creates a new instance of the Product bean
*/
public Product() {}


private int code;

/**
* Sets the product inventory code
* @param code is the product inventory code
*/
public void setCode(int code) {
this.code = code;
}

/**
* Returns the product inventory code
* @return the product inventory code
*/
public int getCode() {
return code;
}

private String name;

/**
* Sets the product name
* @param name is the product name
*/
public void setName(String name) {
this.name = name;
}

/**
* Returns the product name
* @return the product name
*/
public String getName() {
return name;
}

private boolean testedOnAnimals;

/**
* Sets the flag that indicates if the product was tested on animals
* @param testedOnAnimals is the flag that indicates if the product
was tested on animals
*/
public void setTestedOnAnimals(boolean testedOnAnimals) {
this.testedOnAnimals = testedOnAnimals;
}

/**
* Returns the flag that indicates if the product was tested on
animals
* @return the flag that indicates if the product was tested on
animals
*/
public boolean isTestedOnAnimals() {
return testedOnAnimals;
}

private java.util.Date availableSince;

/**
* Sets the date when the company started offering this product to
its customers
* @param availableSince is the date when the company started
offering this product to its customers
*/
public void setAvailableSince(java.util.Date availableSince) {
this.availableSince = availableSince;
}

/**
* Returns the date when the company started offering this product
to its customers
* @return the date when the company started offering this product
to its customers
*/
public java.util.Date getAvailableSince() {
return availableSince;
}

}


总结：
1. 在熟悉了xsl的基本使用之后，理解以上的内容并不是困难；
2. 这样做是比较适合预先知道了某些逻辑功能，但由于某种原因，需要动态生成，或者是为了节省不必要的重复工作，可以通过它自动生成代码；
3. 修改这个xsl比较方便。