使用xsl来动态生成java代码

使用xsl来动态生成java代码

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--- 使用xsl来动态生成java代码 (http://www.webasp.net/article/7/6960.htm)

-- 作者：未知
-- 发布日期： 2003-07-26

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）：
[code]
<?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>
[/code]

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：
[code]
<?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">


<xsl:output method = "text"/>


<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>
[/code]

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：
[code]
/**
* 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;
    }

}
[/code]

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。

sjoy

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