SAX解析xml簡單demo
阿新 • • 發佈：2018-12-12
學習筆記：
基於事件驅動,逐條解析，讀取一點解析一點，適用於只讀取不修改dom結構，佔用記憶體小。
- xml格式如下：
<?xml version="1.0" encoding="UTF-8"?> <beans> <bean id="1" class="com.lvzheng.channel.bean.Book"> <property name="author" value="惡犬"/> <property name="name" value="我與虎謀早餐"/> <property name="price">10.0</property> </bean> <bean id="2" class="com.lvzheng.channel.bean.Book"> <property name="author" value="飛雪"/> <property name="name" value="蜀內大雨連綿"/> <property name="price">15.0</property> </bean> </beans> - 建立xml事件處理器
import com.alibaba.fastjson.JSON; import org.apache.commons.collections.MapUtils; import org.apache.commons.lang3.StringUtils; import org.xml.sax.Attributes; import org.xml.sax.SAXException; import org.xml.sax.helpers.DefaultHandler; import java.lang.reflect.Field; import java.util.*; /** * xml事件處理器 * 可以實現ContentHandler 或者繼承DefaultHandler * 最好繼承DefaultHandler，因為實現ContentHandler需要實現所有的方法 * 而DefaultHandler本身是一個實現了ContentHandler 介面的類，空實現了所有的方法 * 繼承DefaultHandler只需要重寫需要的方法即可 */ public class BookHandler extends DefaultHandler { private List<Object> objList; private String clazz; private Map<String, String> map; private String content = StringUtils.EMPTY; private String name; /** * 文件解析前呼叫，只會被呼叫一次 * * @throws SAXException */ @Override public void startDocument() throws SAXException { System.out.println("==開始解析xml檔案=="); } /** * 標籤節點開始解析時呼叫 * * @param uri * @param localName * @param qName 標籤名稱 * @param attributes 標籤的屬性集 * @throws SAXException */ @Override public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { // 解析至名字為bean的節點時，建立物件 if (StringUtils.equalsIgnoreCase(qName, "beans")) { objList = new ArrayList<>(); map = new HashMap<>(); } else if (StringUtils.equalsIgnoreCase(qName, "bean")) { String id = attributes.getValue("id"); clazz = attributes.getValue("class"); map.put("id", id); } else if (StringUtils.equalsIgnoreCase(qName, "property")) { name = attributes.getValue("name"); String value = attributes.getValue("value"); map.put(name, value); } } /** * 解析標籤內容的時候呼叫 * * @param ch 當前讀取內容的位元組陣列 * @param start 位元組開始位置 * @param length 當前讀取內容的長度 * @throws SAXException */ @Override public void characters(char[] ch, int start, int length) throws SAXException { // 獲取節點內容 content = new String(ch, start, length); } /** * 標籤節點結束時呼叫 * * @param uri * @param localName * @param qName * @throws SAXException */ @Override public void endElement(String uri, String localName, String qName) throws SAXException { if (StringUtils.equalsIgnoreCase(qName, "bean")) { setProperty(); } else if (StringUtils.equalsIgnoreCase(qName, "property")) { if (StringUtils.isNotBlank(content)) { map.put(name, content); } name = StringUtils.EMPTY; } } /** * 文件解析結束後呼叫，只會呼叫一次 * * @throws SAXException */ @Override public void endDocument() throws SAXException { System.out.println("==結束解析xml檔案=="); System.out.println(JSON.toJSON(objList)); } private void setProperty() { if (StringUtils.isBlank(clazz)) { return; } try { Class<?> aClass = Class.forName(clazz); Object obj = aClass.newInstance(); Field[] fields = aClass.getDeclaredFields(); for (Field field : fields) { Object object = MapUtils.getObject(map, field.getName()); if (Objects.nonNull(object)) { field.setAccessible(true); if (Objects.equals(obj, Integer.class)) { field.setInt(field.getName(), Integer.valueOf((String) object)); } else if (Objects.equals(field.getType(), String.class)) { field.set(obj, object); } } } objList.add(obj); map.clear(); } catch (Exception e) { e.printStackTrace(); } } }
3.建立測試類
import org.xml.sax.XMLReader; import javax.xml.parsers.SAXParser; import javax.xml.parsers.SAXParserFactory; public class TestSax { public static void main(String[] args) throws Exception { // 建立sax解析器工廠 SAXParserFactory factory = SAXParserFactory.newInstance(); // 建立sax解析器 SAXParser saxParser = factory.newSAXParser(); // 建立xml讀取器 XMLReader reader = saxParser.getXMLReader(); BookHandler bh = new BookHandler(); // 繫結事件處理器 reader.setContentHandler(bh); reader.parse("src/main/resources/beans.xml"); } }
spring中使用的是sax解析，對bean標籤的解析最為複雜
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
// 解析bean標籤
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
// 解析id屬性
String id = ele.getAttribute(ID_ATTRIBUTE);
// 解析name屬性
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List<String> aliases = new ArrayList<>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isDebugEnabled()) {
logger.debug("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
if (containingBean == null) {
checkNameUniqueness(beanName, aliases, ele);
}
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
// 如果不存在beanName，按照spring的規則生成beanName
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
beanName = this.readerContext.generateBeanName(beanDefinition);
// Register an alias for the plain bean class name, if still possible,
// if the generator returned the class name plus a suffix.
// This is expected for Spring 1.2/2.0 backwards compatibility.
String beanClassName = beanDefinition.getBeanClassName();
if (beanClassName != null &&
beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
aliases.add(beanClassName);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Neither XML 'id' nor 'name' specified - " +
"using generated bean name [" + beanName + "]");
}
}
catch (Exception ex) {
error(ex.getMessage(), ele);
return null;
}
}
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}@Nullable
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
// 解析元資料
parseMetaElements(ele, bd);
// 解析 lookup-method
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
// 解析 replace-method
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
// 解析構造器
parseConstructorArgElements(ele, bd);
// 解析property
parsePropertyElements(ele, bd);
// 解析qualifier
parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
catch (ClassNotFoundException ex) {
error("Bean class [" + className + "] not found", ele, ex);
}
catch (NoClassDefFoundError err) {
error("Class that bean class [" + className + "] depends on not found", ele, err);
}
catch (Throwable ex) {
error("Unexpected failure during bean definition parsing", ele, ex);
}
finally {
this.parseState.pop();
}
return null;
}