Tomcat 8（八）Tomcat解析server.xml的工具—Digester

Tomcat是利用Digester解析server.xml。Digester是Apache下的开源项目

Digester官网：http://commons.apache.org/proper/commons-digester/

使用Digester，需要依赖一些jar包。Digester依赖的jar包可以从网上下载，也可以使用Tomcat提供的jar包

方案一：从网上下载jar包

commons-beanutils.jar

commons-digester.jar

commons-logging.jar

commons-collections.jar(下载commons-collections-3。commons-collections-4将commons-collections的package命名由org.apache.commons.collections改为org.apache.commons.collections4，而Digester内部仍按org.apache.commons.collections使用的)

方案二：使用Tomcat目录下的jar包

tomcat-juli.jar($CATALINA_HOME\bin)

tomcat-util.jar($CATALINA_HOME\lib)

tomcat-util-scan.jar($CATALINA_HOME\lib)

本文采用方案一

下面来看看Digester如何解析School.xml

<?xml version='1.0' encoding='utf-8'?><School name="CSDN"><Grade name="1"><Class name="1" number="31"/><Class name="2" number="32"/></Grade><Grade name="2"><Class name="1" number="41"/><Class name="2" number="42"/></Grade></School>

School是School.xml的最顶层节点，School节点下包含Grade节点，Grade节点下包含Class节点。(学校下有两个年级，每个年级下有两个班级，班级下的number表示人数)

首先要创建与School.xml中各个节点对应的实体类School.java、Grade.java、Class.java(这些类都放在digester包下)

School.java

package digester;public class School {private String name;private Grade grades[] = new Grade[0];private final Object servicesLock = new Object();public void addGrade(Grade g){synchronized (servicesLock) {Grade results[] = new Grade[grades.length + 1];            System.arraycopy(grades, 0, results, 0, grades.length);            results[grades.length] = g;            grades = results;        }}public Grade[] getGrades() {return grades;}public String getName() {return name;}public void setName(String name) {this.name = name;}}

School里的Grade数组用来存放School包含的Grade。调用School. addGrade(Grade g)，可以往Grade数组添加Grade

Grade.java

package digester;public class Grade {private String name;private Class classes[] = new Class[0];private final Object servicesLock = new Object();public void addClass(Class c){synchronized (servicesLock) {Class results[] = new Class[classes.length + 1];            System.arraycopy(classes, 0, results, 0, classes.length);            results[classes.length] = c;            classes = results;        }}public Class[] getClasses() {return classes;}public String getName() {return name;}public void setName(String name) {this.name = name;}}

Class.java

package digester;public class Class {private String name;private int number;public String getName() {return name;}public void setName(String name) {this.name = name;}public int getNumber() {return number;}public void setNumber(int number) {this.number = number;}}

然后创建测试类DigesterTest.java。DigesterTest.java的digester方法用来读取School.xml、创建Digester并设置规则、解析School.xml；print方法用来打印School的信息

package digester;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import org.apache.tomcat.util.digester.Digester;import org.xml.sax.InputSource;import org.xml.sax.SAXException;public class DigesterTest {private School school;public School getSchool() {return school;}public void setSchool(School s) {this.school = s;}public void digester() throws IOException, SAXException{//读取School.xmlFile file = new File("D:\\School.xml");InputStream inputStream = new FileInputStream(file);InputSource inputSource = new InputSource(file.toURI().toURL().toString());;inputSource.setByteStream(inputStream);//创建Digester    Digester digester = new Digester();    //是否需要用DTD验证XML文档的合法性    digester.setValidating(false);    //将当前对象放到对象堆的最顶层    digester.push(this);        /* 下面开始为Digester创建匹配规则     * 在Digester内School、School/Grade、School/Grade/Class     * 分别对应School.xml的School、Grade、Class节点     */        //为School创建规则    /*     * Digester.addObjectCreate(String pattern, String className, String attributeName)     * pattern--匹配的节点     * className--该节点对应的默认实体类     * attributeName--如果该节点有className属性,用className的值替换默认实体类     * Digester匹配到School节点，如果School节点没有className属性，将创建digester.School对象；如果School节点有className属性，将创建指定的(className属性的值)对象    */    digester.addObjectCreate("School",                "digester.School",                "className");    //将指定节点的属性映射到对象，即将School节点的name的属性映射到School.java    digester.addSetProperties("School");    /*     * Digester.addSetNext(String pattern, String methodName, String paramType)     * pattern--匹配的节点     * methodName--调用父节点的方法     * paramType--父节点的方法接收的参数类型     * Digester匹配到School节点，将调用DigesterTest(School的父节点)的setSchool方法，参数为School对象     */    digester.addSetNext("School",           "setSchool",           "digester.School");        //为School/Grade创建规则    digester.addObjectCreate("School/Grade",                "digester.Grade",                "className");    digester.addSetProperties("School/Grade");    //Grade的父节点为School    digester.addSetNext("School/Grade",           "addGrade",           "digester.Grade");        //为School/Grade/Class创建规则    digester.addObjectCreate("School/Grade/Class",                "digester.Class",                "className");    digester.addSetProperties("School/Grade/Class");    digester.addSetNext("School/Grade/Class",           "addClass",           "digester.Class");    digester.parse(inputSource);}//打印School信息public void print(School s){if(s!=null){System.out.println(s.getName() + "有" + s.getGrades().length + "个年级");for(int i=0;i<s.getGrades().length;i++){if(s.getGrades()[i] !=null){Grade g = s.getGrades()[i];System.out.println(g.getName() + "年级 有 " + g.getClasses().length + "个班：");for(int j=0;j<g.getClasses().length;j++){if(g.getClasses()[j] !=null){Class c = g.getClasses()[j];System.out.println(c.getName() + "班有" + c.getNumber() + "人");}}}}}}public static void main(String[] args) throws IOException, SAXException {DigesterTest digesterTest = new DigesterTest();digesterTest.digester();digesterTest.print(digesterTest.school);}}

DigesterTest的输出：

CSDN有2个年级1年级 有 2个班：1班有31人2班有32人2年级 有 2个班：1班有41人2班有42人

Tomcat解析server.xml是在Catalina的load方法内进行的。load方法可以划分成三步：

1. 创建Digester并设置规则

load方法内通过Digester digester = createStartDigester()创建Digester 并设置规则。createStartDigester也是Catalina内的方法

createStartDigester方法的内容(为了简介，每种创建规则的方式各列一个)

protected Digester createStartDigester() {        Digester digester = new Digester();        digester.setValidating(false);        digester.setRulesValidation(true);        HashMap<Class<?>, List<String>> fakeAttributes = new HashMap<>();        ArrayList<String> attrs = new ArrayList<>();        attrs.add("className");        fakeAttributes.put(Object.class, attrs);        digester.setFakeAttributes(fakeAttributes);        digester.setUseContextClassLoader(true);        digester.addObjectCreate("Server",                                 "org.apache.catalina.core.StandardServer",                                 "className");        digester.addSetProperties("Server");        //父节点为Catalinadigester.addSetNext("Server",                            "setServer",                            "org.apache.catalina.Server");        digester.addObjectCreate("Server/Service",                                 "org.apache.catalina.core.StandardService",                                 "className");        digester.addSetProperties("Server/Service");//父节点为Server        digester.addSetNext("Server/Service",                            "addService",                            "org.apache.catalina.Service");//为Connector节点创建规则        digester.addRule("Server/Service/Connector",                         new ConnectorCreateRule());        /* * 如果某个节点包含的规则比较多，可以为该节点创建一个规则类 * 执行digester.addRuleSet(new EngineRuleSet("Server/Service/"))  * 可以将EngineRuleSet内包含的规则，添加到当前digester中 */        digester.addRuleSet(new EngineRuleSet("Server/Service/"));//为Cluster节点创建规则        addClusterRuleSet(digester, "Server/Service/Engine/Host/Cluster/");    }

2. 读取server.xml文件

InputSource inputSource = null;        InputStream inputStream = null;        File file = null;        try {            file = configFile();            inputStream = new FileInputStream(file);            inputSource = new InputSource(file.toURI().toURL().toString());        } catch (Exception e) {            if (log.isDebugEnabled()) {                log.debug(sm.getString("catalina.configFail", file), e);            }        }

3. 利用Digester解析xml文件

try {            inputSource.setByteStream(inputStream);            digester.push(this);            digester.parse(inputSource);        } catch (SAXParseException spe) {            log.warn("Catalina.start using " + getConfigFile() + ": " +                    spe.getMessage());            return;        } catch (Exception e) {            log.warn("Catalina.start using " + getConfigFile() + ": " , e);            return;        } finally {            try {                inputStream.close();            } catch (IOException e) {                // Ignore            }        }

参考文章：

http://blog.csdn.net/caihaijiang/article/details/5944955

http://www.cnblogs.com/bjzhanghao/archive/2005/03/25/125747.html