大家好，又见面了，我是你们的朋友全栈君。

Java 解析 XML

标签： Java基础

XML解析技术有两种 DOM SAX

• DOM方式
  根据XML的层级结构在内存中分配一个树形结构,把XML的标签,属性和文本等元素都封装成树的节点对象
  
  • 优点: 便于实现增 删 改 查
  • 缺点: XML文件过大可能造成内存溢出
• SAX方式
  采用事件驱动模型边读边解析:从上到下一行行解析,解析到某一元素, 调用相应解析方法
  
  • 优点: 不会造成内存溢出,
  • 缺点: 查询不方便,但不能实现 增 删 改

不同的公司和组织提供了针对DOM和SAX两种方式的解析器

• SUN的jaxp
• Dom4j组织的dom4j(最常用:如Spring)
• JDom组织的jdom
  关于这三种解析器渊源可以参考java解析xml文件四种方式.

JAXP 解析

JAXP是JavaSE的一部分,在javax.xml.parsers包下,分别针对dom与sax提供了如下解析器:

• Dom
  
  • DocumentBuilder
  • DocumentBuilderFactory
• SAX
  
  • SAXParser
  • SAXParserFactory

示例XML如下,下面我们会使用JAXP对他进行增 删 改 查操作

• config.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE beans SYSTEM "constraint.dtd">
<beans>
    <bean id="id1" class="com.fq.domain.Bean">
        <property name="isUsed" value="true"/>
    </bean>
    <bean id="id2" class="com.fq.domain.ComplexBean">
        <property name="refBean" ref="id1"/>
    </bean>
</beans>

• constraint.dtd

<!ELEMENT beans (bean*) >
        <!ELEMENT bean (property*)>
        <!ATTLIST bean
                id CDATA #REQUIRED
                class CDATA #REQUIRED
                >

        <!ELEMENT property EMPTY>
        <!ATTLIST property
                name CDATA #REQUIRED
                value CDATA #IMPLIED
                ref CDATA #IMPLIED>

JAXP-Dom

/** * @author jifang * @since 16/1/13下午11:24. */
public class XmlRead { 
   

    @Test
    public void client() throws ParserConfigurationException, IOException, SAXException {
        // 生成一个Dom解析器
        DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();

        // 解析XML文件
        Document document = builder.parse(ClassLoader.getSystemResourceAsStream("config.xml"));

        // ...
    }
}

DocumentBuilder的parse(String/File/InputSource/InputStream param)方法可以将一个XML文件解析为一个Document对象,代表整个文档.
Document(org.w3c.dom包下)是一个接口,其父接口为Node, Node的其他子接口还有Element Attr Text等.

• Node

• Document

Dom查询

• 解析<bean/>标签上的所有属性

public class XmlRead { 
   

    private Document document;

    @Before
    public void setUp() throws ParserConfigurationException, IOException, SAXException {
        document = DocumentBuilderFactory.newInstance().newDocumentBuilder()
                .parse(ClassLoader.getSystemResourceAsStream("config.xml"));
    }

    @Test
    public void client() throws ParserConfigurationException, IOException, SAXException {
        NodeList beans = document.getElementsByTagName("bean");
        for (int i = 0; i < beans.getLength(); ++i) {
            NamedNodeMap attributes = beans.item(i).getAttributes();
            scanNameNodeMap(attributes);
        }
    }

    private void scanNameNodeMap(NamedNodeMap attributes) {
        for (int i = 0; i < attributes.getLength(); ++i) {
            Attr attribute = (Attr) attributes.item(i);
            System.out.printf("%s -> %s%n", attribute.getName(), attribute.getValue());
            // System.out.println(attribute.getNodeName() + " -> " + attribute.getTextContent());
        }
    }
}

• 打印XML文件所有标签名

@Test
public void client() {
    list(document, 0);
}

private void list(Node node, int depth) {
    if (node.getNodeType() == Node.ELEMENT_NODE) {
        for (int i = 0; i < depth; ++i)
            System.out.print("\t");
        System.out.println("<" + node.getNodeName() + ">");
    }

    NodeList childNodes = node.getChildNodes();
    for (int i = 0; i < childNodes.getLength(); ++i) {
        list(childNodes.item(i), depth + 1);
    }
}

Dom添加节点

• 在第一个<bean/>标签下添加一个<property/>标签,最终结果形式:

<bean id="id1" class="com.fq.domain.Bean">
    <property name="isUsed" value="true"/>
    <property name="name" value="simple-bean">新添加的</property>
</bean>

/** * @author jifang * @since 16/1/17 下午5:56. */
public class XmlAppend { 
   

    // 文档回写器
    private Transformer transformer;

    // xml文档
    private Document document;

    @Before
    public void setUp() throws ParserConfigurationException, IOException, SAXException {
        document = DocumentBuilderFactory.newInstance().newDocumentBuilder()
                .parse(ClassLoader.getSystemResourceAsStream("config.xml"));
    }

    @Test
    public void client() {
        // 得到第一bean标签
        Node firstBean = document.getElementsByTagName("bean").item(0);

        /** 创建一个property标签 **/
        Element property = document.createElement("property");

        // 为property标签添加属性
        // property.setAttribute("name", "name");
        // property.setAttribute("value", "feiqing");
        Attr name = document.createAttribute("name");
        name.setValue("name");
        property.setAttributeNode(name);
        Attr value = document.createAttribute("value");
        value.setValue("simple-bean");
        property.setAttributeNode(value);

        // 为property标签添加内容
        //property.setTextContent("新添加的");
        property.appendChild(document.createTextNode("新添加的"));

        // 将property标签添加到bean标签下
        firstBean.appendChild(property);
    }

    @After
    public void tearDown() throws TransformerException {
        transformer = TransformerFactory.newInstance().newTransformer();

        // 写回XML
        transformer.transform(new DOMSource(document),
                new StreamResult("src/main/resources/config.xml"));
    }
}

注意: 必须将内存中的DOM写回XML文档才能生效

Dom更新节点

• 将刚刚添加的<property/>修改如下

<property name="name" value="new-simple-bean">simple-bean是新添加的</property>

@Test
public void client() {
    NodeList properties = document.getElementsByTagName("property");
    for (int i = 0; i < properties.getLength(); ++i) {
        Element property = (Element) properties.item(i);
        if (property.getAttribute("value").equals("simple-bean")) {
            property.setAttribute("value", "new-simple-bean");
            property.setTextContent("simple-bean是新添加的");
            break;
        }
    }
}

Dom删除节点

删除刚刚修改的<property/>标签

@Test
public void client() {
    NodeList properties = document.getElementsByTagName("property");
    for (int i = 0; i < properties.getLength(); ++i) {
        Element property = (Element) properties.item(i);
        if (property.getAttribute("value").equals("new-simple-bean")) {
            property.getParentNode().removeChild(property);
            break;
        }
    }
}

JAXP-SAX

SAXParser实例需要从SAXParserFactory实例的newSAXParser()方法获得, 用于解析XML文件的parse(String uri, DefaultHandler dh)方法没有返回值,但比DOM方法多了一个事件处理器参数DefaultHandler:

• 解析到开始标签,自动调用DefaultHandler的startElement()方法;
• 解析到标签内容(文本),自动调用DefaultHandler的characters()方法;
• 解析到结束标签,自动调用DefaultHandler的endElement()方法.

Sax查询

• 打印整个XML文档

/** * @author jifang * @since 16/1/17 下午9:16. */
public class SaxRead { 
   

    @Test
    public void client() throws ParserConfigurationException, IOException, SAXException {
        SAXParser parser = SAXParserFactory.newInstance().newSAXParser();
        parser.parse(ClassLoader.getSystemResourceAsStream("config.xml"), new SaxHandler());
    }

    private class SaxHandler extends DefaultHandler { 
   

        @Override
        public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
            System.out.print("<" + qName);
            for (int i = 0; i < attributes.getLength(); ++i) {
                String attrName = attributes.getQName(i);
                String attrValue = attributes.getValue(i);
                System.out.print(" " + attrName + "=" + attrValue);
            }
            System.out.print(">");
        }

        @Override
        public void characters(char[] ch, int start, int length) throws SAXException {
            System.out.print(new String(ch, start, length));
        }

        @Override
        public void endElement(String uri, String localName, String qName) throws SAXException {
            System.out.print("</" + qName + ">");
        }
    }
}

• 打印所有property标签内容的Handler

private class SaxHandler extends DefaultHandler { 
   
    // 用互斥锁保护isProperty变量
    private boolean isProperty = false;
    private Lock mutex = new ReentrantLock();

    @Override
    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
        if (qName.equals("property")) {
            mutex.lock();
            isProperty = true;
        }
    }

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        // 只有被锁定之后才有可能是true
        if (isProperty) {
            System.out.println(new String(ch, start, length));
        }
    }

    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException {
        if (qName.equals("property")) {
            try {
                isProperty = false;
            } finally {
                mutex.unlock();
            }
        }
    }
}

注: SAX方式不能实现增 删 改操作.

Dom4j解析

Dom4j是JDom的一种智能分支,从原先的JDom组织中分离出来,提供了比JDom功能更加强大,性能更加卓越的Dom4j解析器(比如提供对XPath支持).
使用Dom4j需要在pom中添加如下依赖:

<dependency>
    <groupId>dom4j</groupId>
    <artifactId>dom4j</artifactId>
    <version>1.6.1</version>
</dependency>

示例XML如下,下面我们会使用Dom4j对他进行增 删 改 查操作:

• config.xml

<?xml version="1.0" encoding="utf-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.fq.me/context" xsi:schemaLocation="http://www.fq.me/context http://www.fq.me/context/context.xsd">
    <bean id="id1" class="com.fq.benz">
        <property name="name" value="benz"/>
    </bean>
    <bean id="id2" class="com.fq.domain.Bean">
        <property name="isUsed" value="true"/>
        <property name="complexBean" ref="id1"/>
    </bean>
</beans>

• context.xsd

<?xml version="1.0" encoding="utf-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.fq.me/context" elementFormDefault="qualified">
    <element name="beans">
        <complexType>
            <sequence>
                <element name="bean" maxOccurs="unbounded">
                    <complexType>
                        <sequence>
                            <element name="property" maxOccurs="unbounded">
                                <complexType>
                                    <attribute name="name" type="string" use="required"/>
                                    <attribute name="value" type="string" use="optional"/>
                                    <attribute name="ref" type="string" use="optional"/>
                                </complexType>
                            </element>
                        </sequence>
                        <attribute name="id" type="string" use="required"/>
                        <attribute name="class" type="string" use="required"/>
                    </complexType>
                </element>
            </sequence>
        </complexType>
    </element>
</schema>

/** * @author jifang * @since 16/1/18下午4:02. */
public class Dom4jRead { 
   

    @Test
    public void client() throws DocumentException {
        SAXReader reader = new SAXReader();
        Document document = reader.read(ClassLoader.getSystemResource("config.xml"));
        // ...
    }
}

与JAXP类似Document也是一个接口(org.dom4j包下),其父接口是Node, Node的子接口还有Element Attribute Document Text CDATA Branch等

• Node

• Document

• Element

• Branch

Dom4j查询

• 打印所有属性信息:

/** * @author jifang * @since 16/1/18下午4:02. */
public class Dom4jRead { 
   

    private Document document;

    @Before
    public void setUp() throws DocumentException {
        document = new SAXReader()
                .read(ClassLoader.getSystemResource("config.xml"));
    }

    @Test
    @SuppressWarnings("unchecked")
    public void client() {
        Element beans = document.getRootElement();

        for (Iterator iterator = beans.elementIterator(); iterator.hasNext(); ) {
            Element bean = (Element) iterator.next();
            String id = bean.attributeValue("id");
            String clazz = bean.attributeValue("class");
            System.out.println("id: " + id + ", class: " + clazz);

            scanProperties(bean.elements());
        }
    }

    public void scanProperties(List<? extends Element> properties) {
        for (Element property : properties) {
            System.out.print("name: " + property.attributeValue("name"));
            Attribute value = property.attribute("value");
            if (value != null) {
                System.out.println("," + value.getName() + ": " + value.getValue());
            }
            Attribute ref = property.attribute("ref");
            if (ref != null) {
                System.out.println("," + ref.getName() + ": " + ref.getValue());
            }
        }
    }
}

Dom4j添加节点

在第一个<bean/>标签末尾添加<property/>标签

<bean id="id1" class="com.fq.benz"> 
    <property name="name" value="benz"/>  
    <property name="refBean" ref="id2">新添加的标签</property>
</bean>  

/** * @author jifang * @since 16/1/19上午9:50. */
public class Dom4jAppend { 
   

    //...

    @Test
    public void client() {
        Element beans = document.getRootElement();
        Element firstBean = beans.element("bean");
        Element property = firstBean.addElement("property");
        property.addAttribute("name", "refBean");
        property.addAttribute("ref", "id2");
        property.setText("新添加的标签");
    }

    @After
    public void tearDown() throws IOException {
        // 回写XML
        OutputFormat format = OutputFormat.createPrettyPrint();
        XMLWriter writer = new XMLWriter(new FileOutputStream("src/main/resources/config.xml"), format);
        writer.write(document);
    }
}

我们可以将获取读写XML操作封装成一个工具, 以后调用时会方便些:

/** * @author jifang * @since 16/1/19下午2:12. */
public class XmlUtils { 
   

    public static Document getXmlDocument(String config) {
        try {
            return new SAXReader().read(ClassLoader.getSystemResource(config));
        } catch (DocumentException e) {
            throw new RuntimeException(e);
        }
    }

    public static void writeXmlDocument(String path, Document document) {
        try {
            new XMLWriter(new FileOutputStream(path), OutputFormat.createPrettyPrint()).write(document);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

• 在第一个<bean/>的第一个<property/>后面添加一个<property/>标签

<bean id="id1" class="com.fq.benz"> 
    <property name="name" value="benz"/>  
    <property name="rate" value="3.14"/>
    <property name="refBean" ref="id2">新添加的标签</property> 
</bean>  

public class Dom4jAppend { 
   

    private Document document;

    @Before
    public void setUp() {
        document = XmlUtils.getXmlDocument("config.xml");
    }

    @Test
    @SuppressWarnings("unchecked")
    public void client() {
        Element beans = document.getRootElement();
        Element firstBean = beans.element("bean");
        List<Element> properties = firstBean.elements();

        //Element property = DocumentHelper
        // .createElement(QName.get("property", firstBean.getNamespaceURI()));
        Element property = DocumentFactory.getInstance()
                .createElement("property", firstBean.getNamespaceURI());
        property.addAttribute("name", "rate");
        property.addAttribute("value", "3.14");
        properties.add(1, property);
    }

    @After
    public void tearDown() {
        XmlUtils.writeXmlDocument("src/main/resources/config.xml", document);
    }
}

Dom4j修改节点

• 将id1 bean的第一个<property/>修改如下:

<property name="name" value="翡青"/>  

@Test
@SuppressWarnings("unchecked")
public void client() {
    Element beans = document.getRootElement();
    Element firstBean = beans.element("bean");
    List<Element> properties = firstBean.elements();

    Element property = DocumentFactory.getInstance()
            .createElement("property", firstBean.getNamespaceURI());
    property.addAttribute("name", "rate");
    property.addAttribute("value", "3.14");
    properties.add(1, property);
}

Dom4j 删除节点

• 删除刚刚修改的节点

@Test
@SuppressWarnings("unchecked")
public void delete() {
    List<Element> beans = document.getRootElement().elements("bean");
    for (Element bean : beans) {
        if (bean.attributeValue("id").equals("id1")) {
            List<Element> properties = bean.elements("property");
            for (Element property : properties) {
                if (property.attributeValue("name").equals("name")) {
                    // 执行删除动作
                    property.getParent().remove(property);
                    break;
                }
            }
            break;
        }
    }
}

Dom4j实例

在Java 反射一文中我们实现了根据JSON配置文件来加载bean的对象池,现在我们可以为其添加根据XML配置(XML文件同前):

/** * @author jifang * @since 16/1/18下午9:18. */
public class XmlParse { 
   

    private static final ObjectPool POOL = ObjectPoolBuilder.init(null);

    public static Element parseBeans(String config) {
        try {
            return new SAXReader().read(ClassLoader.getSystemResource(config)).getRootElement();
        } catch (DocumentException e) {
            throw new RuntimeException(e);
        }
    }

    public static void processObject(Element bean, List<? extends Element> properties)
            throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchFieldException {
        Class<?> clazz = Class.forName(bean.attributeValue(CommonConstant.CLASS));
        Object targetObject = clazz.newInstance();

        for (Element property : properties) {
            String fieldName = property.attributeValue(CommonConstant.NAME);
            Field field = clazz.getDeclaredField(fieldName);
            field.setAccessible(true);
            // 含有value属性
            if (property.attributeValue(CommonConstant.VALUE) != null) {
                SimpleValueSetUtils.setSimpleValue(field, targetObject, property.attributeValue(CommonConstant.VALUE));
            } else if (property.attributeValue(CommonConstant.REF) != null) {
                String refId = property.attributeValue(CommonConstant.REF);
                Object object = POOL.getObject(refId);
                field.set(targetObject, object);
            } else {
                throw new RuntimeException("neither value nor ref");
            }
        }

        POOL.putObject(bean.attributeValue(CommonConstant.ID), targetObject);
    }
}

注: 上面代码只是对象池项目的XML解析部分,完整项目可参考git@git.oschina.net:feiqing/commons-frame.git

XPath

XPath是一门在XML文档中查找信息的语言,XPath可用来在XML文档中对元素和属性进行遍历.

谓语: 谓语用来查找某个特定的节点或者包含某个指定的值的节点.

XPath的语法详细内容可以参考W3School XPath 教程.

Dom4j对XPath的支持

默认的情况下Dom4j并不支持XPath, 需要在pom下添加如下依赖:

<dependency>
    <groupId>jaxen</groupId>
    <artifactId>jaxen</artifactId>
    <version>1.1.6</version>
</dependency>

Dom4jNode接口提供了方法对XPath支持:

XPath实现查询

• 查询所有bean标签上的属性值

/** * @author jifang * @since 16/1/20上午9:28. */
public class XPathRead { 
   

    private Document document;

    @Before
    public void setUp() throws DocumentException {
        document = XmlUtils.getXmlDocument("config.xml");
    }

    @Test
    @SuppressWarnings("unchecked")
    public void client() {
        List<Element> beans = document.selectNodes("//bean");
        for (Element bean : beans) {
            System.out.println("id: " + bean.attributeValue("id") +
                    ", class: " + bean.attributeValue("class"));
        }
    }
}

XPath实现更新

• 删除id=”id2”的<bean/>

@Test
public void client() {
    Node bean = document.selectSingleNode("//bean[@id=\"id2\"]");
    bean.getParent().remove(bean);
}

参考:

Dom4j的使用

Java 处理 XML 的三种主流技术及介绍