Digester解析XML文件
TOMCAT底层解析server.xml使用。
Dom4j是把一个xml文件全部读取到内存中,构建成一个DOM树来解析,所以Dom4j适合读取比较小的xml文件。
SAX是基于文件流来解析xml文件的,在读取xml文件流时,SAX会通过节点来触发相应的操作,也可以说SAX是基于文件流的事情触发机制来解析xml文件的。
Digeter是apache的common项目,作用是将XML转化成对象,使用者直接从对象中获取xml的节点信息。Digester是对SAX的包装,它也是基于文件流来解析xml文件,只不过这些解析操作对用户是透明的。Tomcat的配置文件conf/server.xml就是用Digester来读取的。
一般用来读取xml文件的工具包有DOM、SAX和JDOM等,但用过的人都知道,它们属于比较底层的API,写起来代码量很大,而且如果修改了xml文件的格式,代码也要做大幅度的改动。而使用Apache Jakarta的Digester,解析XML文件非常方便且不需要过多的关心底层的具体解析过程。Digester本来仅仅是Jakarta Struts中的一个工具,用于处理struts-config.xml配置文件。显然,将XML文件转换成相应的Java对象是一项很通用的功能,这个工具理应具有更广泛的用途,所以很快它就在Jakarta Commons项目(用于提供可重用的Java组件库)中有了一席之地。Digester由"事件"驱动,通过调用预定义的规则操作对象栈,将XML文件转换为Java对象。
工作原理如下:
Digester底层采用SAX(Simple API for XML)析XML文件,所以很自然的,对象转换由"事件"驱动,在遍历每个节点时,检查是否有匹配模式,如果有,则执行规则定义的操作,比如创建特定的Java对象,或调用特定对象的方法等。此处的XML元素根据匹配模式(matching pattern)识别,而相关操作由规则(rule)定义。
如下xml代码,右边是左边元素对应的匹配模式:
<datasources> 'datasources' <datasource> 'datasources/datasource' <name/> 'datasources/datasource/name' <driver/> 'datasources/datasource/driver' </datasource> <datasource> 'datasources/datasource' <name/> 'datasources/datasource/name' <driver/> 'datasources/datasource/driver' </datasource> </datasources>
Tomcat与Digester的关系(注意该博客,很多资源)
Tomcat源码的catalina中利用Digester解析conf/server.xml
Digester处理多层的XML(仔细分析)
==============================================================================
<?xml version="1.0" encoding="UTF-8?> <database> <user userName="guest" password="guest"> </user> </database>
1.addObjectCreate(String rule,Class class)
设置节点与Java对象的映射规则,rule指定节点的筛选规则,class设置映射对象。SAX解析时,遇到rule指定的节节点,会创建一个class实例放入堆栈中。
比如:digester.addObectCreate("database/user","com.model.UserBean").解析遇到user节点时,会创建一个UserBean实例并放入堆栈中。
2.addSetProperties(String rule)
设置节点的属性设置规则。当解析遇到符合rule的节点时,根据属性列表中的属性值对,使用Java反射机制使用标准的JavaBean方法设置栈顶对象实例;
比如:digester.addSetProperties("database/user"),解析遇到user节点时,会获取键值对 userName=guest,password=guest,获得栈顶的UserBean对象,设置实例的userName、password属性;
解析元素上的属性
3.addBeanPropertySetter(String rule)
该方法的作用及使用方法类似于addSetProperties,只不过它是用rule所指定的标签来调用对象的setter。
该方法在tomcat6中貌似没有。
tomcat6中Digester类路径为:import org.apache.tomcat.util.digester.Digester;
不为:import org.apache.commons.digester.Digester;
4.addSetNext(String rule,String methodName)
设置当前rule节点与父节点的调用规则,当遇到rule节点时,调用堆栈中的次栈顶元素调用methodName方法。将栈顶元素作为次顶元素指定方法的输入参数。
比如:digester.addSetNext("database/user","addUser"),调用database实例的addUser,user为参数
5.addCallMethod(String rule,String methodName,int paraNumber)
该方法同样设置对象的属性,但更加灵活,不需要对象具有setter
根据rule规则指定的属性,调用对象的methodName方法,paraNumber参数是表示方法需要的参数个数,当paraNumber=0时,可以单独使用,不然需要配合addCallParam方法
比如:digester.addCallMethod("database/user/uerName","setUserName",0);
6.addCallParam(String rule,int paraIndex,String attributeName)
该方法与addCallMethod配合使用,根据rule指定的标签属性来调用方法
paraIndex表明需要填充的方法形参序号,从0开始,方法由addCallMethdo指定,attributeName指定标签属性名;
使用注意事项:
1.Digester类调用的顺序,必须与XML数据文件绝对一致;
2.Digester类依赖于JavaBean规范,类必须符合规范;
3.XML文件中标签/属性的名称必须与Bean中的一致(包括大小写);
==================================================================
关键方法说明
(1) serverDigester.addObjectCreate("Server","com.test.server.digester.Server")
当解析xml文件时,遇到“Server”就初始化一个“com.test.server.digester.Server”对象,并且把该对象压入栈顶
(2) serverDigester.addSetProperties("Server", "port", "port")
给Server对象注册port属性,当解析到Server节点的port属性时调用Server的setPort方法
(3) serverDigester.addSetNext("Server/Listener", "addListener","com.test.server.digester.Listener")
当解析Server节点下的Listener节点的时候,调用Server对象的addListener方法,把当前Listener对象写入到Server对象中。无论Server节点下有多少个Listener节点,都会调用addListener方法
(4) serverDigester.addCallMethod("Server/Service/Engine", "setEngine", 0)
Service中添加Engine,调用当前top object的setEngine函数,参数个数为0
addCallMethod与addBeanPropertySetter方法等价
Example1:
<?xml version="1.0" encoding="ISO-8859-1"?> <student name="llin" age="16" grade="3"> <subject name="math" teacher="yu" /> </student>
package digester;
import java.util.ArrayList;
public class Student {
private String name;
private int age;
private int grade;
private ArrayList<Subject> list = new ArrayList();
public Student (){
System.out.println("A student go to school");
}
public void add ( Subject subjects ){
System.out.println("add Subjects " + subjects.getName() + " to the Student: "+ this.getName());
list.add( subjects );
}
/////////////////////////////////////////////////
public int getAge() {
return age;
}
public void setAge(int age) {
System.out.println( " set age of Student:" + name);
this.age = age;
}
public int getGrade() {
return grade;
}
public void setGrade(int grade) {
System.out.println( " set score of Student:" + name );
this.grade = grade;
}
public String getName() {
return name;
}
public void setName(String name) {
System.out.println(" set name pf Student" );
this.name = name;
}
public ArrayList<Subject> getList (){
return this.list;
}
}
package digester;
public class Subject {
private String name;
private String teacher;
public Subject() {
System.out.println("One subjects waiting scheduling!");
}
public void print() {
System.out.println("Subjects :" + name + "of " + teacher + "in schedule");
}
/////////////////////////////////////////////////////
public String getName() {
return name;
}
public void setName(String name) {
System.out.println(" set name of Subjects:" + name);
this.name = name;
}
public String getTeacher() {
return teacher;
}
public void setTeacher(String teacher) {
System.out.println(" set teacher of Subjects :" + teacher);
this.teacher = teacher;
}
}
package digester;
import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import org.apache.tomcat.util.digester.Digester;
import org.xml.sax.SAXException;
public class StudentDigesterTest {
public static void main ( String [] args ) throws IOException{
unUseRule();
//useRule();
}
public static void unUseRule(){
File xml = new File( "../apache-tomcat-6.0.41-src/test/student.xml");
Digester digester = new Digester();
digester.addObjectCreate( "student" , "digester.Student" );
digester.addSetProperties("student");
digester.addObjectCreate("student/subject" , "digester.Subject");
digester.addSetProperties("student/subject");
//上面该句可用这句代替digester.addSetProperties("student/subject","subject","subject");
/**
* public void addSetProperties(String pattern,String attributeName,String propertyName)
*/
digester.addSetNext("student/subject" , "add" );
Student student = null;
try {
student = (Student)digester.parse(xml);
}catch ( SAXException e ){
System.out.println("parse with mistakes!");
} catch (IOException e) {
e.printStackTrace();
}
Iterator it = student.getList().iterator();
while ( it.hasNext()) {
}
}
public static void useRule(){
File xml = new File( "../apache-tomcat-6.0.41-src/test/student.xml");
Digester digester = new Digester();
digester.addRuleSet(new MyRuleSet());
Student student = null;
try {
student = (Student)digester.parse(xml);
}catch ( SAXException e ){
System.out.println("parse with mistakes!");
} catch (IOException e) {
e.printStackTrace();
}
Iterator it = student.getList().iterator();
while ( it.hasNext()) {
}
}
}
package digester;
import org.apache.tomcat.util.digester.Digester;
import org.apache.tomcat.util.digester.RuleSetBase;
public class MyRuleSet extends RuleSetBase{
@Override
public void addRuleInstances(Digester digester) {
digester.addObjectCreate( "student" , "digester.Student" );
digester.addSetProperties("student");
digester.addObjectCreate("student/subject" , "digester.Subject");
digester.addSetProperties("student/subject");
digester.addSetNext("student/subject" , "add" );
}
}
两种方法结果都为:
Example2:
viewcache2.xml:
<?xml version="1.0" encoding="UTF-8" ?> <viewcache> <areas> <area id="1098" parentId="1001" areaType="province" name="上海" ordering="1867" phoneArea="111"/> <area id="1099" parentId="1098" areaType="capital" name="北京" ordering="1868" phoneArea="010"/> </areas> </viewcache>
package digester;
import java.util.ArrayList;
import java.util.List;
public class ViewCache {
private ArrayList<Area> areaList = new ArrayList<Area>();
public ArrayList getAreaList() {
return areaList;
}
public void setAreaList(ArrayList areaList) {
this.areaList = areaList;
}
// 供Digester调用的方法
public void addArea(Area area) {
System.out.println("addArea..");
this.areaList.add(area);
}
}
package digester;
public class Area {
private int id;
private String name;
private String areaType;
private int parentId;
private int ordering;
// private String zip;
private String phoneArea;
public Area(){
System.out.println("Area constructor..");
}
public int getId() {
return id;
}
public void setId(int id) {
System.out.println( " set id of Area:" + id);
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
System.out.println( " set name of Area:" + name);
this.name = name;
}
public String getAreaType() {
return areaType;
}
public void setAreaType(String areaType) {
System.out.println( " set areaType of Area:" + areaType);
this.areaType = areaType;
}
public int getParentId() {
return parentId;
}
public void setParentId(int parentId) {
System.out.println( " set parentId of Area:" + parentId);
this.parentId = parentId;
}
public int getOrdering() {
return ordering;
}
public void setOrdering(int ordering) {
System.out.println( " set ordering of Area:" + ordering);
this.ordering = ordering;
}
/*public String getZip() {
return zip;
}
public void setZip(String zip) {
this.zip = zip;
}*/
public String getPhoneArea() {
return phoneArea;
}
public void setPhoneArea(String phoneArea) {
System.out.println( " set phoneArea of Area:" + phoneArea);
this.phoneArea = phoneArea;
}
}
package digester;
import java.io.IOException;
import org.apache.tomcat.util.digester.Digester;
import org.xml.sax.SAXException;
public class AreaDigester {
public ViewCache digester() throws Exception {
Digester digester = new Digester();
digester.setValidating(false);
digester.addObjectCreate("viewcache/areas", ViewCache.class);
// 指明匹配模式和要创建的类
digester.addObjectCreate("viewcache/areas/area", Area.class);
//使用这句可以打印出Area字段set值时的syso语句,下面的打印不出,没搞清楚。。。
digester.addSetProperties("viewcache/areas/area");
// digester.addSetProperties("viewcache/areas/area/id");
// digester.addSetProperties("viewcache/areas/area/parentId", "parentId", "parentId");
// digester.addSetProperties("viewcache/areas/area/name", "name", "name");
// digester.addSetProperties("viewcache/areas/area/areaType", "areaType", "areaType");
// digester.addSetProperties("viewcache/areas/area/ordering", "ordering", "ordering");
// //digester.addSetProperties("viewcache/areas/area/zip", "zip", "zip");
// digester.addSetProperties("viewcache/areas/area/phoneArea", "phoneArea", "phoneArea");
// 当移动到下一个标签中时的动作
digester.addSetNext("viewcache/areas/area", "addArea");
ViewCache vc = null;
try {
vc = (ViewCache) digester.parse("../apache-tomcat-6.0.41-src/test/viewcache2.xml");
} catch (IOException e) {
throw new Exception(e);
} catch (SAXException e) {
throw new Exception(e);
}
return vc;
}
public static void main(String[] args) {
AreaDigester m = new AreaDigester();
ViewCache vc = null;
try {
vc = m.digester();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
结果: