mybatis xpath实现

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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。

 

 

    
        
        Neal Stephenson
        Spectra
        0553380958
        14.95
    
 
    
        
        Larry Niven
        Jerry Pournelle
        Pocket
        0743416910
        5.99
    
 
    
        
        Neal Stephenson
        Spectra
        0553573862
        7.50
    

 

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 evalNodes(String expression) {
    return evalNodes(document, expression);
  }

  public List evalNodes(Object root, String expression) {
    List xnodes = new ArrayList();
    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。