mybatis xpath实现

tubaobaoya3

　　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()");
　　[size=1em]//book[author='Neal Stephenson'book标签 下的text为[size=1em]Neal Stephenson的[size=1em]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([size=1em]validation[size=1em]);
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。