mybatis xpath实现 博客分类: xpathmybatis mybatisxpath
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2024-03-14 08:38:52
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Java 5 推出了 javax.xml.xpath 包,这是一个用于 XPath 文档查询的独立于 XML 对象模型的库。
强大的xpath表达式支持对xml document文档检索信息。
<?xml version="1.0" encoding="UTF-8"?> <inventory> <book year="2000"> <title>Snow Crash</title> <author>Neal Stephenson</author> <publisher>Spectra</publisher> <isbn>0553380958</isbn> <price>14.95</price> </book> <book year="2005"> <title>Burning Tower</title> <author>Larry Niven</author> <author>Jerry Pournelle</author> <publisher>Pocket</publisher> <isbn>0743416910</isbn> <price>5.99</price> </book> <book year="1995"> <title>Zodiac</title> <author>Neal Stephenson</author> <publisher>Spectra</publisher> <isbn>0553573862</isbn> <price>7.50</price> </book> </inventory>
import java.io.IOException; import org.w3c.dom.*; import org.xml.sax.SAXException; import javax.xml.parsers.*; import javax.xml.xpath.*; public class XPathExample { public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException, XPathExpressionException { //创建 XPathFactory: DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance(); domFactory.setNamespaceAware(true); // never forget this! DocumentBuilder builder = domFactory.newDocumentBuilder(); Document doc = builder.parse("book.xml"); XPathFactory factory = XPathFactory.newInstance(); //这个工厂创建 XPath 对象: XPath xpath = factory.newXPath(); //设置命名空间 // xpath.setNamespaceContext(new PersonalNamespaceContext()); //XPath 对象编译 XPath 表达式: XPathExpression expr = xpath.compile("//book[author='Neal Stephenson']/title/text()"); //doc是整个节点 /** * XPathConstants.NODESET XPathConstants.BOOLEAN XPathConstants.NUMBER XPathConstants.STRING XPathConstants.NODE 定义了返回类型 xpath 和java的映射关系 number 映射为 java.lang.Double string 映射为 java.lang.String boolean 映射为 java.lang.Boolean node-set 映射为 org.w3c.dom.NodeList */ Object result = expr.evaluate(doc, XPathConstants.NODESET); //类型转换 NodeList nodes = (NodeList) result; for (int i = 0; i < nodes.getLength(); i++) { System.out.println(nodes.item(i).getNodeValue()); } } }
xpath 表达式代码
XPathExpression expr = xpath.compile("//book[author='Neal Stephenson']/title/text()");
//book[author='Neal Stephenson'book标签 下的text为Neal Stephenson的author标签
/title/test()是title 标签的文本
很简单吧,再说一下
实体解析器SAX EntityResolver
这里有它详细的解释:http://www.ibm.com/developerworks/cn/xml/tips/x-tipent/
让xml文档包含外部实体引用
package com.ibm.developerWorks; import org.xml.sax.EntityResolver; import org.xml.sax.InputSource; import org.xml.sax.SAXException; public class CopyrightResolver implements EntityResolver { public InputSource resolveEntity(String publicID, String systemID) throws SAXException { if (systemID.equals("http://www.ibm.com/developerworks/copyright.xml")) { // Return local copy of the copyright.xml file return new InputSource("/usr/local/content/localCopyright.xml"); } // If no match, returning null makes process continue normally return null; }
再你的xml解析类中每次解析都会调用这个方法,这样就避免了每次都要加载外部资源的消耗。
xpase的公用类:
import java.io.InputStream; import java.io.Reader; import java.io.StringReader; import java.util.ArrayList; import java.util.List; import java.util.Properties; import javax.xml.namespace.QName; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.xpath.XPath; import javax.xml.xpath.XPathConstants; import javax.xml.xpath.XPathFactory; import org.apache.ibatis.builder.BuilderException; import org.w3c.dom.Document; import org.w3c.dom.Node; import org.w3c.dom.NodeList; import org.xml.sax.EntityResolver; import org.xml.sax.ErrorHandler; import org.xml.sax.InputSource; import org.xml.sax.SAXException; import org.xml.sax.SAXParseException; public class XPathParser { private Document document;//dom对象 private boolean validation;//是否验证 domFactory.setNamespaceAware(validation); private EntityResolver entityResolver;//实体解析器 private Properties variables;//配置文件 private XPath xpath;//xpath public XPathParser(String xml) { commonConstructor(false, null, null);//初始化XPath对象 this.document = createDocument(new InputSource(new StringReader(xml)));//获取dom对象 } public XPathParser(Reader reader) { commonConstructor(false, null, null); this.document = createDocument(new InputSource(reader)); } public XPathParser(InputStream inputStream) { commonConstructor(false, null, null); this.document = createDocument(new InputSource(inputStream)); } public XPathParser(Document document) { commonConstructor(false, null, null); this.document = document; } public XPathParser(String xml, boolean validation) { commonConstructor(validation, null, null); this.document = createDocument(new InputSource(new StringReader(xml))); } public XPathParser(Reader reader, boolean validation) { commonConstructor(validation, null, null); this.document = createDocument(new InputSource(reader)); } public XPathParser(InputStream inputStream, boolean validation) { commonConstructor(validation, null, null); this.document = createDocument(new InputSource(inputStream)); } public XPathParser(Document document, boolean validation) { commonConstructor(validation, null, null); this.document = document; } public XPathParser(String xml, boolean validation, Properties variables) { commonConstructor(validation, variables, null); this.document = createDocument(new InputSource(new StringReader(xml))); } public XPathParser(Reader reader, boolean validation, Properties variables) { commonConstructor(validation, variables, null); this.document = createDocument(new InputSource(reader)); } public XPathParser(InputStream inputStream, boolean validation, Properties variables) { commonConstructor(validation, variables, null); this.document = createDocument(new InputSource(inputStream)); } public XPathParser(Document document, boolean validation, Properties variables) { commonConstructor(validation, variables, null); this.document = document; } public XPathParser(String xml, boolean validation, Properties variables, EntityResolver entityResolver) { commonConstructor(validation, variables, entityResolver); this.document = createDocument(new InputSource(new StringReader(xml))); } public XPathParser(Reader reader, boolean validation, Properties variables, EntityResolver entityResolver) { commonConstructor(validation, variables, entityResolver); this.document = createDocument(new InputSource(reader)); } public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) { commonConstructor(validation, variables, entityResolver); this.document = createDocument(new InputSource(inputStream)); } public XPathParser(Document document, boolean validation, Properties variables, EntityResolver entityResolver) { commonConstructor(validation, variables, entityResolver); this.document = document; } public void setVariables(Properties variables) { this.variables = variables; } public String evalString(String expression) { return evalString(document, expression); } public String evalString(Object root, String expression) { String result = (String) evaluate(expression, root, XPathConstants.STRING); result = PropertyParser.parse(result, variables); return result; } public Boolean evalBoolean(String expression) { return evalBoolean(document, expression); } public Boolean evalBoolean(Object root, String expression) { return (Boolean) evaluate(expression, root, XPathConstants.BOOLEAN); } public Short evalShort(String expression) { return evalShort(document, expression); } public Short evalShort(Object root, String expression) { return Short.valueOf(evalString(root, expression)); } public Integer evalInteger(String expression) { return evalInteger(document, expression); } public Integer evalInteger(Object root, String expression) { return Integer.valueOf(evalString(root, expression)); } public Long evalLong(String expression) { return evalLong(document, expression); } public Long evalLong(Object root, String expression) { return Long.valueOf(evalString(root, expression)); } public Float evalFloat(String expression) { return evalFloat(document, expression); } public Float evalFloat(Object root, String expression) { return Float.valueOf(evalString(root, expression)); } public Double evalDouble(String expression) { return evalDouble(document, expression); } public Double evalDouble(Object root, String expression) { return (Double) evaluate(expression, root, XPathConstants.NUMBER); } public List<XNode> evalNodes(String expression) { return evalNodes(document, expression); } public List<XNode> evalNodes(Object root, String expression) { List<XNode> xnodes = new ArrayList<XNode>(); NodeList nodes = (NodeList) evaluate(expression, root, XPathConstants.NODESET); for (int i = 0; i < nodes.getLength(); i++) { xnodes.add(new XNode(this, nodes.item(i), variables)); } return xnodes; } public XNode evalNode(String expression) { return evalNode(document, expression); } public XNode evalNode(Object root, String expression) { Node node = (Node) evaluate(expression, root, XPathConstants.NODE); if (node == null) { return null; } return new XNode(this, node, variables); } private Object evaluate(String expression, Object root, QName returnType) { try { return xpath.evaluate(expression, root, returnType); } catch (Exception e) { throw new BuilderException("Error evaluating XPath. Cause: " + e, e); } } private Document createDocument(InputSource inputSource) { // important: this must only be called AFTER common constructor try { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); factory.setValidating(validation); factory.setNamespaceAware(false); factory.setIgnoringComments(true); factory.setIgnoringElementContentWhitespace(false); factory.setCoalescing(false); factory.setExpandEntityReferences(true); DocumentBuilder builder = factory.newDocumentBuilder(); builder.setEntityResolver(entityResolver);//设置实体解析器 builder.setErrorHandler(new ErrorHandler() { public void error(SAXParseException exception) throws SAXException { throw exception; } public void fatalError(SAXParseException exception) throws SAXException { throw exception; } public void warning(SAXParseException exception) throws SAXException { } }); return builder.parse(inputSource); } catch (Exception e) { throw new BuilderException("Error creating document instance. Cause: " + e, e); } } private void commonConstructor(boolean validation, Properties variables, EntityResolver entityResolver) { this.validation = validation; this.entityResolver = entityResolver; this.variables = variables; XPathFactory factory = XPathFactory.newInstance(); this.xpath = factory.newXPath(); } }
这里用到了一个字符串解析器:
PropertyParser 它是来处理字符串中${}这样的字符,去配置文件中查找。
解析器模式:
import java.util.Properties; public class PropertyParser { public static String parse(String string, Properties variables) { VariableTokenHandler handler = new VariableTokenHandler(variables); GenericTokenParser parser = new GenericTokenParser("${", "}", handler); return parser.parse(string); } private static class VariableTokenHandler implements TokenHandler { private Properties variables; public VariableTokenHandler(Properties variables) { this.variables = variables; } public String handleToken(String content) { if (variables != null && variables.containsKey(content)) { return variables.getProperty(content); } return "${" + content + "}"; } } }
GenericTokenParser.java
public class GenericTokenParser { private final String openToken; private final String closeToken; private final TokenHandler handler; public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) { this.openToken = openToken; this.closeToken = closeToken; this.handler = handler; } public String parse(String text) { StringBuilder builder = new StringBuilder(); if (text != null && text.length() > 0) {//如果传入的字符串有值 //将字符串转为字符数组 char[] src = text.toCharArray(); int offset = 0; //判断openToken在text中的位置,注意indexOf函数的返回值-1表示不存在,0表示在在开头的位置 int start = text.indexOf(openToken, offset); while (start > -1) { if (start > 0 && src[start - 1] == '\\') { //如果text中在openToken前存在转义符就将转义符去掉。如果openToken前存在转义符,start的值必然大于0,最小也为1 //因为此时openToken是不需要进行处理的,所以也不需要处理endToken。接着查找下一个openToken builder.append(src, offset, start - 1).append(openToken); offset = start + openToken.length();//重设offset } else { int end = text.indexOf(closeToken, start); if (end == -1) {//如果不存在openToken,则直接将offset位置后的字符添加到builder中 builder.append(src, offset, src.length - offset); offset = src.length;//重设offset } else { builder.append(src, offset, start - offset);//添加openToken前offset后位置的字符到bulider中 offset = start + openToken.length();//重设offset String content = new String(src, offset, end - offset);//获取openToken和endToken位置间的字符串 builder.append(handler.handleToken(content));//调用handler进行处理 offset = end + closeToken.length();//重设offset } } start = text.indexOf(openToken, offset);//开始下一个循环 } //只有当text中不存在openToken且text.length大于0时才会执行下面的语句 if (offset < src.length) { builder.append(src, offset, src.length - offset); } } return builder.toString(); } }
简单的说,这个函数的作用就是将openToken和endToken间的字符串取出来用handler处理下,然后再拼接到一块。我们接下来看一个具体的handler,了解下它对传入的字符串做了怎样的处理。
在XMLConfigBuilder这个类中有它的调用实例:
//很关键是xpath的表达式语言 匹配对象 放入configuration中 private void parseConfiguration(XNode root) { try { propertiesElement(root.evalNode("properties")); //issue #117 read properties first typeAliasesElement(root.evalNode("typeAliases")); pluginElement(root.evalNode("plugins")); objectFactoryElement(root.evalNode("objectFactory")); objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); settingsElement(root.evalNode("settings")); environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631 databaseIdProviderElement(root.evalNode("databaseIdProvider")); typeHandlerElement(root.evalNode("typeHandlers")); mapperElement(root.evalNode("mappers")); } catch (Exception e) { throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); } }
这里使用了解析器设计模式,这里的文件可以单独作为我们以后对xml文件解析的使用。