Apache Digester应用实例

一直想把它写下来,可是总有点懒

这次介绍一下digester的常用法,其他更高级的使用方法请参阅digester doc(由于比较忙,下次有时间写一篇关于cglib的常用法,呵呵)
Apache Digester应用实例 [原创]
--------------利用 apache commons-digester 自动根据xml文件创建java 对象
<day day up>
author: binker
email: binker_cao@163.com
date: 2006/12/16
note: 本文可以任意转载,但请保持其完整性并注明来源,谢谢.

一.序
Digester是apache的一个组件 apache commons-digester.jar,通过它可以很方便的从xml文件生成java对象.你不用再象以前通过jdom或者Xerces去读取一个document对象.(jdom和Xerces仍然有它们的用武之地及强大之处,在其它应用里你也少不了它们)
我只是用一个例子展示一下如何把xml文件生成一个java object.
首先你必须把jar加入到你的项目classpath.
(一)准备:
1.环境: Eclipse, jdk1.4+
2.需求说明：学院包含学生和老师，学生可以选修课程，老师有不同的资格认证。
3.Java Class的定义，简洁起见，略去import内容。
4.使用Digester生成java对象 必须要定义一个xml文件，此xml文件必须符合digester-rules.dtd的规则。
5.所有的xml文件必须在classpath路径中，这样可以通过Class.getClassLoader().getInputStream()读取xml文件。

(二)提要:
本示例所需的java class 和 xml文件分成四类:
1.基础xml文件: [academy.xml]: 你将要解析的xml文件.
2.基础java class: [Academy.java, Teacher.java, Student.java, Cousre.java]: 生成的对象的类定义
3.digesterRules.xml: [academyRules.xml]: 定义了基础xml文件到基础java class的匹配(映射)关系
4.Digester class: [DigestXMLJavaAcademy.java]: 根据digesterRules.xml去解析基础xml文件,并生成java 对象

(三)参考资料
1.English ebook: Pro Jakarta Commons by Harshad Oak Apress 2004

二.基础Java Class
1.学院 class Academy.java

代码

public class Academy {

private Vector students;

private Vector teachers;

private String name;

public Academy() {

students = new Vector();

teachers = new Vector();

}

public void addStudent(Student student) {

students.addElement(student);

}

public void addTeacher(Teacher teacher) {

teachers.addElement(teacher);

}

public Vector getStudents() {

return students;

}

public void setStudents(Vector newStudents) {

students = newStudents;

}

public Vector getTeachers() {

return teachers;

}

public void setTeachers(Vector newTeachers) {

teachers = newTeachers;

}

public String getName() {

return name;

}

public void setName(String newName) {

name = newName;

}

}

render_code();

============================================================
2.学生 Student.java

代码

public class Student {

private Vector courses;

private String name;

private String division;

public Student() {

courses = new Vector();

}

public void addCourse(Course course) {

courses.addElement(course);

}

public String getName() {

return name;

}

public void setName(String newName) {

name = newName;

}

public String getDivision() {

return division;

}

public void setDivision(String newDivision) {

division = newDivision;

}

public void setCourses(Vector courses) {

this.courses = courses;

}

public Vector getCourses() {

return courses;

}

}

render_code();

============================================================
3.老师 Teacher.java

代码

public class Teacher {

private String name;

private Vector certifications;

public Teacher() {

certifications = new Vector();

}

public void addCertification(String certification) {

certifications.addElement(certification);

}

public String getName() {

return name;

}

public void setName(String newName) {

name = newName;

}

public void setCertifications(Vector certifications) {

this.certifications = certifications;

}

public Vector getCertifications() {

return certifications;

}

}

render_code();

============================================================
4.课程 Course.java

代码

public class Course {

private String id;

private String name;

public Course() {

}

public String getId() {

return id;

}

public void setId(String newId) {

id = newId;

}

public String getName() {

return name;

}

public void setName(String newName) {

name = newName;

}

}

render_code();

三.基础XML文件
============================================================
学院 academy.xml,包含了学生(包含了课程),老师

代码

<?xml version="1.0"?>

<academy name="JAcademy" >

<student name="JavaBoy" division="A">

<course>

<id>C1</id>

<name>JSP</name>

</course>

<course>

<id>C2</id>

<name>Servlets</name>

</course>

</student>

<student name="JavaGirl" division="B">

<course>

<id>C3</id>

<name>EJB</name>

</course>

</student>

<teacher name="JavaGuru">

<certification>SCJP</certification>

<certification>SCWCD</certification>

</teacher>

<teacher name="JavaMaster">

<certification>OCP</certification>

<certification>SCJP</certification>

<certification>SCEA</certification>

</teacher>

</academy>

render_code();

============================================================

四.Digester Class
DigestXMLJavaAcademy.java 和academyRules.xml
其中academyRules.xml用来定义xml文件和java对象的匹配(映射)关系,格式要符合digester-rules.dtd格式约束
DigestXMLJavaAcademy.java 根据academyRules.xml解析academy.xml文件并生成 Academy对象.
============================================================

代码

1. academyRules.xml

<?xml version="1.0"?>

<digester-rules>

<pattern value="academy">

<object-create-rule classname="com.commonsbook.chap7.academy.Academy" />

<set-properties-rule />

<pattern value="student">

<object-create-rule classname="com.commonsbook.chap7.academy.Student" />

<set-properties-rule />

<pattern value="course">

<object-create-rule classname="com.commonsbook.chap7.academy.Course" />

<bean-property-setter-rule pattern="id"/>

<bean-property-setter-rule pattern="name"/>

<set-next-rule methodname="addCourse" />

</pattern>

<set-next-rule methodname="addStudent" />

</pattern>

<pattern value="teacher">

<object-create-rule classname="com.commonsbook.chap7.academy.Teacher" />

<set-properties-rule />

<call-method-rule pattern="certification" methodname="addCertification"

paramcount="1" />

<call-param-rule pattern="certification" paramnumber="0"/>

<set-next-rule methodname="addTeacher" />

</pattern>

</pattern>

</digester-rules>

render_code();

============================================================
2. DigestXMLJavaAcademy.java

代码

public class DigestXMLJavaAcademy {

public void digest(){

try {

//Create Digester using rules defined in academyRules.xml

Digester digester = DigesterLoader.createDigester(

this.getClass().getClassLoader().getResource("academyRules.xml"));

//Parse academy.xml using the Digester to get an instance of Academy

Academy a = (Academy)digester.parse(

this.getClass().getClassLoader().getResourceAsStream("academy.xml"));

Vector vStud=a.getStudents();

Vector vTeach=a.getTeachers();

for (int i = 0; i < vStud.size(); i++) {

System.out.println("Student>> "+PropertyUtils.describe(vStud.get(i)));

}

for (int i = 0; i < vTeach.size(); i++) {

System.out.println("Teacher>> "+ PropertyUtils.describe(vTeach.get(i)));

}

} catch(Exception e) {

e.printStackTrace();

}

}

public static void main(String[] args) {

DigestXMLJavaAcademy xmlDigest= new DigestXMLJavaAcademy();

xmlDigest.digest();

}

}

render_code();

五.运行结果
自己运行吧,呵呵

六.后记
写下来还真得花点时间呢,不过这也是对自己以前思路的一个整理.
写出来与大家共同分享也是一种乐趣.呵呵.
下次有时间写一篇关于cglib的常用法.