digester解析xml文件

￡神魔★判官ぃ 2022-02-15 12:43 234阅读 0赞

**正文**

在我们的项目中或多或少会采用xml来做配置文件，你可以采用Java原生支持的sax、DOM或者第三方的dom4j等。虽然提供了各式各样的解析方式，但是解析一个复杂的xml所编写的Java代码是非常麻烦的，尤其是当xml做了修改，你会发现你又要修改Java代码。

Apache的commons项目中Digester项目解决了这个问题，它可以很轻易地将xml文件解析成Java对象，让你直接去使用，而你仅仅需要去预定义一份解析规则。

而对于解析规则，你可以采用Java的方式定义、xml的方式定义亦或者annotation的方式定义。

要使用digester需要引入依赖：

<dependency>
                <groupId>org.apache.commons</groupId>
                <artifactId>commons-digester3</artifactId>
                <version>3.2</version>
            </dependency>

假设我们要解析如下school.xml文件

![复制代码][copycode.gif]

<?xml version="1.0" encoding="utf-8" ?>
    <school>
        <classes>
            <class className="classOne">
                <student>
                    <no>1</no>
                    <name>小张</name>
                    <age>24</age>
                </student>
                <student>
                    <no>2</no>
                    <name>小李</name>
                    <age>24</age>
                </student>
                <student>
                    <no>1</no>
                    <name>小王</name>
                    <age>24</age>
                </student>
            </class>
        </classes>
    </school>

![复制代码][copycode.gif]

我们需要预定义Student、Class、School节点的Java类与之对应

![复制代码][copycode.gif]

package cn.lay.demo.digester.definition;
    
    /**
     * 学生节点
     * @author lay
     * @date 2018/10/16 23:35
     */
    public class StudentDefinition {
    
        private Integer no;
    
        private String name;
    
        private Integer age;
    
        public Integer getNo() {
            return no;
        }
    
        public void setNo(Integer no) {
            this.no = no;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "StudentDefinition{" +
                    "no=" + no +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
    
    package cn.lay.demo.digester.definition;
    
    import java.util.ArrayList;
    import java.util.List;
    
    /**
     * 班级节点
     * @author lay
     * @date 2018/10/16 23:36
     */
    public class ClassDefinition {
    
        private String className;
    
        private List<StudentDefinition> studentDefinitionList = new ArrayList<>();
    
        public String getClassName() {
            return className;
        }
    
        public void setClassName(String className) {
            this.className = className;
        }
    
        public List<StudentDefinition> getStudentDefinitionList() {
            return studentDefinitionList;
        }
    
        public void setStudentDefinitionList(List<StudentDefinition> studentDefinitionList) {
            this.studentDefinitionList = studentDefinitionList;
        }
    
        public void addStudent(StudentDefinition studentDefinition) {
            studentDefinitionList.add(studentDefinition);
        }
    
        @Override
        public String toString() {
            return "ClassDefinition{" +
                    "className='" + className + '\'' +
                    ", studentDefinitionList=" + studentDefinitionList +
                    '}';
        }
    }
    
    package cn.lay.demo.digester.definition;
    
    import java.util.ArrayList;
    import java.util.List;
    
    /**
     * 学校节点
     * @author lay
     * @date 2018/10/16 23:37
     */
    public class SchoolDefinition {
    
        private List<ClassDefinition> classDefinitions = new ArrayList<>();
    
        public List<ClassDefinition> getClassDefinitions() {
            return classDefinitions;
        }
    
        public void setClassDefinitions(List<ClassDefinition> classDefinitions) {
            this.classDefinitions = classDefinitions;
        }
    
        public void addClass(ClassDefinition classDefinition) {
            classDefinitions.add(classDefinition);
        }
    
        @Override
        public String toString() {
            return "SchoolDefinition{" +
                    "classDefinitions=" + classDefinitions +
                    '}';
        }
    }

![复制代码][copycode.gif]

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## 1、Java方式配置解析规则 ##

rule

![复制代码][copycode.gif]

package cn.lay.demo.digester.rule;
    
    import cn.lay.demo.digester.definition.ClassDefinition;
    import cn.lay.demo.digester.definition.SchoolDefinition;
    import cn.lay.demo.digester.definition.StudentDefinition;
    import org.apache.commons.digester3.Digester;
    
    import java.net.URL;
    
    /**
     * java方式定义解析规则
     * @author lay
     * @date 2018/10/16 23:38
     */
    public class DigesterRule {
    
        /**
         * 解析
         * @param filePath
         * @return
         */
        public SchoolDefinition execute(String filePath) throws Exception{
            Digester digester = new Digester();
            digester.setValidating(false);
            // classes node
            digester.addObjectCreate("school/classes", SchoolDefinition.class);
            // class node
            digester.addObjectCreate("school/classes/class", ClassDefinition.class);
            // set properties
            digester.addSetProperties("school/classes/class");
            // student node
            digester.addObjectCreate("school/classes/class/student", StudentDefinition.class);
            // set properties
            digester.addBeanPropertySetter("school/classes/class/student/no");
            digester.addBeanPropertySetter("school/classes/class/student/name");
            digester.addBeanPropertySetter("school/classes/class/student/age");
            // add student
            digester.addSetNext("school/classes/class/student", "addStudent");
            // add class
            digester.addSetNext("school/classes/class", "addClass");
            // parse
            URL url = this.getClass().getClassLoader().getResource(filePath);
            System.out.println("url=" + url.toString());
            return digester.parse(url);
        }
    }

![复制代码][copycode.gif]

测试

@Test
        public void testJavaRule() throws Exception {
            SchoolDefinition schoolDefinition = new DigesterRule().execute("school.xml");
            System.out.println(schoolDefinition);
        }

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## 2、xml方式配置解析规则 ##

rule

![复制代码][copycode.gif]

<!DOCTYPE digester-rules PUBLIC
            "-//Apache Commons //DTD digester-rules XML V1.0//EN"
            "http://commons.apache.org/digester/dtds/digester-rules-3.0.dtd">
    <digester-rules>
        
        <pattern value="school/classes">
            <object-create-rule classname="cn.lay.demo.digester.definition.SchoolDefinition"/>
            
            <pattern value="class">
                <object-create-rule classname="cn.lay.demo.digester.definition.ClassDefinition"/>
                <set-properties-rule/>
                
                <pattern value="student">
                    <object-create-rule classname="cn.lay.demo.digester.definition.StudentDefinition"/>
                    <bean-property-setter-rule pattern="no"/>
                    <bean-property-setter-rule pattern="name"/>
                    <bean-property-setter-rule pattern="age"/>
                    <set-next-rule methodname="addStudent"/>
                </pattern>
                <set-next-rule methodname="addClass"/>
            </pattern>
        </pattern>
    
    </digester-rules>

![复制代码][copycode.gif]

测试

![复制代码][copycode.gif]

@Test
        public void testXmlRule() throws Exception {
            Digester digester = DigesterLoader.newLoader(new XmlRulesModule()).newDigester();
            URL url = this.getClass().getClassLoader().getResource("school.xml");
            System.out.println("url=" + url);
            SchoolDefinition schoolDefinition = digester.parse(url);
            System.out.println(schoolDefinition);
        }
    
        
        class XmlRulesModule extends FromXmlRulesModule {
    
            @Override
            protected void loadRules() {
                loadXMLRules(this.getClass().getClassLoader().getResourceAsStream("rule/schoolRule.xml"));
            }
        }

![复制代码][copycode.gif]

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##  3、注解方式配置解析规则 ##

基于零配置思想，digester支持采用annotation来注解相应的解析规则。

rule

![复制代码][copycode.gif]

package cn.lay.demo.digester.definition;
    
    import org.apache.commons.digester3.annotations.rules.ObjectCreate;
    import org.apache.commons.digester3.annotations.rules.SetNext;
    import org.apache.commons.digester3.annotations.rules.SetRoot;
    
    import java.util.ArrayList;
    import java.util.List;
    
    /**
     * 学校节点
     * @author lay
     * @date 2018/10/16 23:37
     */
    @ObjectCreate(pattern = "school/classes")
    public class SchoolDefinition {
    
        private List<ClassDefinition> classDefinitions = new ArrayList<>();
    
        public List<ClassDefinition> getClassDefinitions() {
            return classDefinitions;
        }
    
        public void setClassDefinitions(List<ClassDefinition> classDefinitions) {
            this.classDefinitions = classDefinitions;
        }
    
        @SetNext
        public void addClass(ClassDefinition classDefinition) {
            System.out.println("执行了addClass");
            classDefinitions.add(classDefinition);
        }
    
        @Override
        public String toString() {
            return "SchoolDefinition{" +
                    "classDefinitions=" + classDefinitions +
                    '}';
        }
    }
    
    package cn.lay.demo.digester.definition;
    
    import org.apache.commons.digester3.annotations.rules.*;
    
    import java.util.ArrayList;
    import java.util.List;
    
    /**
     * 班级节点
     * @author lay
     * @date 2018/10/16 23:36
     */
    @ObjectCreate(pattern = "school/classes/class")
    public class ClassDefinition {
    
        @SetProperty(pattern = "school/classes/class")
        private String className;
    
        private List<StudentDefinition> studentDefinitionList = new ArrayList<>();
    
        public String getClassName() {
            return className;
        }
    
        public void setClassName(String className) {
            this.className = className;
        }
    
        public List<StudentDefinition> getStudentDefinitionList() {
            return studentDefinitionList;
        }
    
        public void setStudentDefinitionList(List<StudentDefinition> studentDefinitionList) {
            this.studentDefinitionList = studentDefinitionList;
        }
    
        @SetNext
        public void addStudent(StudentDefinition studentDefinition) {
            System.out.println("执行了addStudent");
            studentDefinitionList.add(studentDefinition);
        }
    
        @Override
        public String toString() {
            return "ClassDefinition{" +
                    "className='" + className + '\'' +
                    ", studentDefinitionList=" + studentDefinitionList +
                    '}';
        }
    }
    
    package cn.lay.demo.digester.definition;
    
    import org.apache.commons.digester3.annotations.rules.BeanPropertySetter;
    import org.apache.commons.digester3.annotations.rules.ObjectCreate;
    
    /**
     * 学生节点
     * @author lay
     * @date 2018/10/16 23:35
     */
    @ObjectCreate(pattern = "school/classes/class/student")
    public class StudentDefinition {
    
        @BeanPropertySetter(pattern = "school/classes/class/student/no")
        private Integer no;
    
        @BeanPropertySetter(pattern = "school/classes/class/student/name")
        private String name;
    
        @BeanPropertySetter(pattern = "school/classes/class/student/age")
        private Integer age;
    
        public Integer getNo() {
            return no;
        }
    
        public void setNo(Integer no) {
            this.no = no;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "StudentDefinition{" +
                    "no=" + no +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

![复制代码][copycode.gif]

测试

![复制代码][copycode.gif]

@Test
        public void testAnnotationRule() throws Exception {
            Digester digester = DigesterLoader.newLoader(new FromAnnotationsRuleModule() {
                @Override
                protected void configureRules() {
                    // 这里只添加SchoolDefinition即可
                    bindRulesFrom(SchoolDefinition.class);
                }
            }).newDigester();
            URL url = this.getClass().getClassLoader().getResource("school.xml");
            System.out.println("url=" + url);
            SchoolDefinition schoolDefinition = digester.parse(url);
            System.out.println(schoolDefinition);
        }

![复制代码][copycode.gif]

[copycode.gif]: /images/20220215/df193d53bab147c28d9fdf1ca5a2b1e4.png
[Link 1]: https://www.cnblogs.com/lay2017/p/9801690.html#_labelTop