Tomcat源码的catalina中利用Digester解析conf/server.xml

http://blog.youkuaiyun.com/wgw335363240/article/details/5869660

最近在学习Tomcat的源码，在catalina. createStartDigester方法中，Tomcat开发人员采用了Digester来读取conf/server.xml文件，以前读取xml文件一般采用Dom4j和SAX。由于对Digester比较陌生，所以今天抽时间研究了一下Digester是如何解析xml文件的。先简单阐述下Dom4j和SAX解析XML的却别：

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、    下载Digester的jar

(1)      Digester的jar下载地址（版本：2.0）
http://commons.apache.org/digester/

(2)      Digester依赖的Logging的jar下载地址（版本：1.1.1）

http://commons.apache.org/logging/

(3)      Digester依赖的BeanUtils的jar下载地址（版本：1.8.3）

http://commons.apache.org/beanutils/

 

只需要按照以上步骤下载jar包后，导入到eclipse工程即可。为了大家省去jar包下载的麻烦，我在博客资源中上传了“Digester_jar”资源，这里面包含了所有需要的jar包和源码。

对应的对象的源码参考我博客资源中的“Digester_object”资源，这里包含了测试代码中需要的Java对象代码。

二、    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

三、    注意事项

Xml中定义的属性要与对象中set和get方法一致，比如xml中定义了一个节点属性“engineType”，那么在java对象的set方法必须为setEngineType，除了首字母外，其他字母必须一致，不然在解析的时候会解析不到对应的属性值。不知道是否还有其他规则，没有摸清楚。

四、    XML解析代码

<?xml version="1.0" encoding="UTF-8" ?> <!--          Attribute must be lower case.          For example:                   attribute :engineType                   Method in Service must be setEngineType(All attribute character but one must be the same with method in PO!)   --> <Server port="9996" debug="0">   <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener"             debug="0"/>   <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener"             debug="1"/>   <Service name="Catalina">     <Engine engineType="12">I am a Engine</Engine>   </Service> </Server>

 

五、    Java对象代码（也可以见博客资源“Digester_object”）

(1)    Server.java代码

/**  *  */ package com.test.server.digester;   import java.util.Vector;   /**  * 模仿解析Tomcat的conf/server.xml中的节点serve类  *  * @author rey  *  */ public class Server {            /**           *构造函数           */          public Server() {                   super();          }            // 成员变量===============================          private int m_nPort = 0;          private int m_nIsDebug = 0;          private Service m_Service = null;          private Vector m_listenerVector = new Vector();            // 公有方法=================================          /**           * @return the m_nPort           */          public int getPort() {                   return m_nPort;          }            /**           * @param mNPort           *            the m_nPort to set           */          public void setPort(int mNPort) {                   m_nPort = mNPort;          }            /**           * @return the m_nIsDebug           */          public int getIsDebug() {                   return m_nIsDebug;          }            /**           * @param mNIsDebug           *            the m_nIsDebug to set           */          public void setIsDebug(int mNIsDebug) {                   m_nIsDebug = mNIsDebug;          }            /**           * @return the m_service           */          public Service getService() {                   return m_Service;          }            /**           * @param mService the m_service to set           */          public void setService(Service mService) {                   m_Service = mService;          }            public void addListener(Listener _listener) {                   m_listenerVector.add(_listener);          }            public Vector getListeners() {                   return m_listenerVector;          } }

 

(2)    Service.java代码

/**  *  */ package com.test.server.digester;   /**  * 模仿解析Tomcat的conf/server.xml中的节点Service类  *  * @author rey  *  */ public class Service {            /**           *           */          public Service() {                   super();          }            // 成员变量===============================          private String m_sName = null;          private String m_sEngine =null;          private String m_sEngineType=null;              // 公有方法=================================            /**           * @return the m_sEngineType           */          public String getEngineType() {                   return m_sEngineType;          }            /**只能有第一个字母大写，如果还有其他的大写，则解析不出来           * @param mSEngineType the m_sEngineType to set           */          public void setEngineType(String mSEngineType) {                   m_sEngineType = mSEngineType;          }            /**           * @return the m_sEngine           */          public String getEngine() {                   return m_sEngine;          }            /**           * @param mSEngine the m_sEngine to set           */          public void setEngine(String mSEngine) {                   m_sEngine = mSEngine;          }                   /**           * @return the m_sName           */          public String getName() {                   return m_sName;          }              /**           * @param mSName           *            the m_sName to set           */          public void setName(String mSName) {                   m_sName = mSName;          } }

(3)    Listener代码

/**  *  */ package com.test.server.digester;   /**  * 模仿解析Tomcat的conf/server.xml中的节点Listener类  *  * @author rey  *  */ public class Listener {            /**           *           */          public Listener() {                   super();          }            // 成员变量===============================            private String m_sClassName = null;          private int m_nIsDebug = 0;            // 公有方法=================================          /**           * @return the m_nIsDebug           */          public int getDebug() {                   return m_nIsDebug;          }            /**           * @param mNIsDebug           *            the m_nIsDebug to set           */          public void setDebug(int mNIsDebug) {                   m_nIsDebug = mNIsDebug;          }            /**           * @return the m_sClassName           */          public String getClassName() {                   return m_sClassName;          }            /**           * @param mSClassName           *            the m_sClassName to set           */          public void setClassName(String mSClassName) {                   m_sClassName = mSClassName;          } }

 

(4)    Engine代码

/**  *  */ package com.test.server.digester;   /**  * 模仿解析Tomcat的conf/server.xml中的节点Engine类  * @author rey  *  */ public class Engine {            /**           *           */          public Engine() {                   super();          }                   // 成员变量===============================          private String m_sName = null;          private int m_nIsDebug = 0;                   // 公有方法=================================          /**           * @return the m_sName           */          public String getName() {                   return m_sName;          }            /**           * @param mSName           *            the m_sName to set           */          public void setName(String mSName) {                   m_sName = mSName;          }          /**           * @return the m_nIsDebug           */          public int getIsDebug() {                   return m_nIsDebug;          }            /**           * @param mNIsDebug           *            the m_nIsDebug to set           */          public void setIsDebug(int mNIsDebug) {                   m_nIsDebug = mNIsDebug;          } }

 

六、    Java解析xml代码

DigesterServer代码：

/**  *  */ package com.test.server.digester;   import java.io.FileInputStream; import java.io.IOException; import java.util.Vector;   import org.apache.commons.digester.Digester; import org.xml.sax.SAXException;   /**  * 用于解析Tomcat的conf/server.xml的Diagester  *  * @author rey  *  */ public class DigesterServer {            /**           * @param args           * @throws SAXException           * @throws IOException           */          public static void main(String[] args) throws IOException, SAXException {                   String sXMLFile = "D://temp//test_diagester.xml";                   Digester serverDigester = new Digester();                   FileInputStream inputXMLStream = new FileInputStream(sXMLFile);                     // 解析Server.xml                   serverDigester.setValidating(false);                     // 注册Server规则,解析XML时，遇到Server，就实例化一个com.test.server.digester.Server对象，并且压栈                   serverDigester.addObjectCreate("Server",                                    "com.test.server.digester.Server");                                     //给Server对象设置一个属性，可以调用setPort进行设置                   serverDigester.addSetProperties("Server", "port", "port");                   serverDigester.addSetProperties("Server", "debug", "debug");                     // 注册Listener规则,这里的斜线是根据xml的path来计算的                   serverDigester.addObjectCreate("Server/Listener",                                    "com.test.server.digester.Listener");                   serverDigester.addSetProperties("Server/Listener", "className",                                    "className");                   serverDigester.addSetProperties("Server/Listener", "debug", "debug");                     // Server对象添加一个Listener对象（无论Server节点下有几个Listener对象，都会添加到Vector中)                   serverDigester.addSetNext("Server/Listener", "addListener",                                    "com.test.server.digester.Listener");                     // 注册Service对象                   serverDigester.addObjectCreate("Server/Service",                                    "com.test.server.digester.Service");                   serverDigester.addSetProperties("Server/Service", "name", "name");                     // server中添加Service                   serverDigester.addSetNext("Server/Service", "setService",                                    "com.test.server.digester.Service");                     // Service中添加Engine,调用当前top object的setEngine函数，参数个数为0                   serverDigester.addCallMethod("Server/Service/Engine", "setEngine", 0);                   serverDigester.addSetProperties("Server/Service/Engine","enginetype","enginetype");                     // 开始解析XML文件                   Server currServer = (Server) serverDigester.parse(inputXMLStream);                   if (currServer == null) {                           System.out.println("currServer==null");                           return;                   }                   Vector listenerVector = currServer.getListeners();                   System.out.println(listenerVector.size());   <span style="font-size