Mybatis的内幕

第一章、入门

<?xml version="1.0" encoding="UTF-8" ?>

上面试mybatis-config.xml配置，下面看BlogMapper.xml的文件结构

<?xml version="1.0" encoding="UTF-8" ?>

java加载配置文件，使用Mybatis的api
package com.example.demo;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class Main {

public static void main(String[] args) throws IOException {
	String resouce = "com/xxx/mybatis-config.xml";
	InputStream inputStream = Resources.getResourceAsStream(resouce);
	SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
	SqlSession session = sqlSessionFactory.openSession();
	try {
		Map<String, Object> parameter = new HashMap<>();
		parameter.put("id", 1);
		Blog blog = (Blog) session.selectOne("com.xxx.BlogMapper.selectBlogDetails", parameter);
		System.out.println(blog);
	} finally {
		session.close();
	}
	
}

}

Mybatis的整体架构分为三层，分别是基础支持层、核心处理层和接口层。

基础支持层包括：反射模块、日志模块、资源加载模块、解析器模块、数据源模块、事务管理、缓存模块、Binding模块。
核心处理层：配置解析、sql解析与scripting解析、sql执行、插件.
接口层：SqlSession接口

第二章、基础支持层
解析器模块：xml常见的解析方式有三种：DOM解析、SAX解析和StAX解析。

Snow Crash
Neal Stephenson
Spectra
0553380958
14.95

Buring Tower
Larry Niven
Pocket
0743416910
5.99

Zodiac
Jerry Pournelle
Spectra
0553573862
7.50

DOM解析
package com.mybatis.part02;

import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.ErrorHandler;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;

public class XPathTest {

public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException, XPathExpressionException {
	DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
	
	documentBuilderFactory.setValidating(true);
	documentBuilderFactory.setNamespaceAware(false);
	documentBuilderFactory.setIgnoringComments(true);
	documentBuilderFactory.setIgnoringElementContentWhitespace(false);
	documentBuilderFactory.setCoalescing(false);
	documentBuilderFactory.setExpandEntityReferences(true);
	
	DocumentBuilder builder = documentBuilderFactory.newDocumentBuilder();
	builder.setErrorHandler(new ErrorHandler() {
		
		@Override
		public void warning(SAXParseException exception) throws SAXException {
			System.out.println("warning:" + exception.getMessage());
		}
		
		@Override
		public void fatalError(SAXParseException exception) throws SAXException {
			System.out.println("fatalError:" + exception.getMessage());
			
		}
		
		@Override
		public void error(SAXParseException exception) throws SAXException {
			System.out.println("error:" + exception.getMessage());
		}
	});
	
	Document document = builder.parse("src/com/mybatis/part02/inventory.xml");
	XPathFactory factory = XPathFactory.newInstance();
	XPath path = factory.newXPath();
	XPathExpression expr = path.compile("//book[author='Neal Stephenson']/title/text()");
	Object result = expr.evaluate(document, XPathConstants.NODESET);
	System.out.println("查询作者的标题是:");
	NodeList nodes = (NodeList) result;
	for (int i = 0; i < nodes.getLength(); i++) {
		System.out.println(nodes.item(i).getNodeValue());
	}
	
	System.out.println("查询1997年之后的标题");
	nodes = (NodeList) path.evaluate("//book[@year > 1997]/title/text()", document, XPathConstants.NODESET);
	for (int i = 0; i < nodes.getLength(); i++) {
		System.out.println(nodes.item(i).getNodeValue());
	}
	
	System.out.println("查询1997年之后图书属性和标题");
	nodes = (NodeList) path.evaluate("//book[@year > 1997]/@*|//book[@year > 1997]/title/text()", document, XPathConstants.NODESET);
	for (int i = 0; i < nodes.getLength(); i++) {
		System.out.println(nodes.item(i).getNodeValue());
	}
}

}

DOM解析的缺点是将整个xml加载到内存中，会耗费较多的内存。
package com.audition;

import java.util.ArrayList;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

public class SAXParserHandler extends DefaultHandler{

String value = null;
Book book = null;
int bookIndex = 0;
private ArrayList<Book> bookList = new ArrayList<Book>();
public ArrayList<Book> getBookList() {
    return bookList;
}

@Override
public void startDocument() throws SAXException {
	
	super.startDocument();
}

@Override
public void endDocument() throws SAXException {
	
	super.endDocument();
}

@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
	
	super.startElement(uri, localName, qName, attributes);
	if (qName.equals("book")) {
		bookIndex++;
		book = new Book();
		int num = attributes.getLength();
		for (int i = 0; i < num; i++) {
			System.out.println(attributes.getQName(i) + ":" 
					+ attributes.getValue(i));
			if (attributes.getQName(i).equals("id")) {
                book.setId(attributes.getValue(i));
            }
		}
	}
}

@Override
public void endElement(String uri, String localName, String qName) throws SAXException {
	// TODO Auto-generated method stub
	super.endElement(uri, localName, qName);
	if (qName.equals("book")) {
		bookList.add(book);
        book = null;
	} else if (qName.equals("name")) {
        book.setName(value);
    }
    else if (qName.equals("author")) {
        book.setAuthor(value);
    }
    else if (qName.equals("year")) {
        book.setYear(value);
    }
    else if (qName.equals("price")) {
        book.setPrice(value);
    }
    else if (qName.equals("language")) {
        book.setLanguage(value);
    }
}

@Override
public void characters(char[] ch, int start, int length) throws SAXException {
	// TODO Auto-generated method stub
	super.characters(ch, start, length);
	if (ch != null) {
		value = new String(ch, start, length);
        if (!value.trim().equals("")) {
            System.out.println("节点值是：" + value);
        }
	}
	
}

}
SAX不存储xml的文档结构

package com.mybatis.part02;

import java.io.InputStream;

import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;

public class StAXTest {

private static InputStream is;
public static void main(String[] args) throws XMLStreamException {
	is=StAXTest.class.getClassLoader().getResourceAsStream("inventory.xml");
	XMLInputFactory factory = XMLInputFactory.newInstance();
	XMLStreamReader streamReader = factory.createXMLStreamReader(is);
	while(streamReader.hasNext()){  
		int eventId=streamReader.next();
		switch (eventId) { 
			case XMLStreamConstants.START_DOCUMENT: 
				System.out.println("start docmuent");
				break;
			case XMLStreamConstants.START_ELEMENT:
				System.out.println("<"+streamReader.getLocalName()+">");
				for(int i=0;i<streamReader.getAttributeCount();i++){ 
					System.out.println(streamReader.getAttributeLocalName(i)+"="+streamReader.getAttributeValue(i));
				}
				break;
			case XMLStreamConstants.CHARACTERS:
				if(streamReader.isWhiteSpace()){
					break;
				}
				System.out.println(streamReader.getText());
				break;
			case XMLStreamConstants.END_ELEMENT:
				System.out.println("</"+streamReader.getLocalName()+">");
				break;
			case XMLStreamConstants.END_DOCUMENT:
				System.out.println("end docmuent");
				break;
			default:
				break;
		}
	}
}

}
拉模型：在遍历文档时，会把感兴趣的部分从读取器中拉出，不需要引发事件，允许我们选择性地处理节点。这大大提高了灵活性，以及整体效率。

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