解析MyBatis配置文件mybatis-config.xml(一)

mybatis 配置文件 mybatis-config.xmljava

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!-- 配置文件的根元素 -->
<configuration>
    <!-- 屬性:定義配置外在化 -->
    <properties></properties>
    <!-- 設置:定義mybatis的一些全局性設置 -->
    <settings>
        <!-- 具體的參數名和參數值 -->
        <setting name="" value=""/>
    </settings>
    <!-- 類型名稱:爲一些類定義別名 -->
    <typeAliases></typeAliases>
    <!-- 類型處理器:定義Java類型與數據庫中的數據類型之間的轉換關係 -->
    <typeHandlers></typeHandlers>
    <!-- 對象工廠 -->
    <objectFactory type=""></objectFactory>
    <!-- 插件:mybatis的插件,插件能夠修改mybatis的內部運行規則 -->
    <plugins>
        <plugin interceptor=""></plugin>
    </plugins>
    <!-- 環境:配置mybatis的環境 -->
    <environments default="">
        <!-- 環境變量:能夠配置多個環境變量,好比使用多數據源時,就須要配置多個環境變量 -->
        <environment id="">
            <!-- 事務管理器 -->
            <transactionManager type=""></transactionManager>
            <!-- 數據源 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://120.78.83.28:3306/test?useUnicode=true&amp;characterEncoding=utf-8&amp;useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="Dsk741852!"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 數據庫廠商標識 -->
    <databaseIdProvider type=""></databaseIdProvider>
    <!-- 映射器:指定映射文件或者映射類 -->
    <mappers></mappers>
</configuration>

 

Mybatis 在初始化過程當中處理mybatis-Config.xml 配置文件以及映射文件時,使用的是DOM解析,並結合XPath 解析XML配置文件。DOM會將整個XML文檔加載到內存並造成數據結構。XPath 是XML查詢語句,實現對XML的解析,功能相似SQL語句。EntityResolver 用於加載本地dtd。mysql

Mybatis 提供的XpathParser 類封裝 前面涉及的XPath,Document 和EntityResolversql

public class XPathParser {

  private Document document;
  private boolean validation;
  private EntityResolver entityResolver;
  private Properties variables;
  private XPath xpath;

默認狀況下,對XML文檔進行驗證時,會根據XML文檔開始位置指定的網址加載對應的DTD文件或XSD文件。當網絡比較慢時,在實踐中提早設置EntityResolver 接口對象加載本地DTD文件。數據庫

package xml;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.parsing.XPathParser;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import java.io.IOException;
import java.io.InputStream;
import java.util.Locale;

/**
 * Created by dingshuangkun on 2017/12/10.
 */
public class XMLMapperEntityResolver implements EntityResolver {

    private static final String IBATIS_CONFIG_SYSTEM="ibatis-3-cofig.dtd";
    private static final String IBATIS_MAPPER_SYSTEM="ibatis-3-mapper.dtd";
    private static final String MYBATIS_CONFIG_SYSTEM="mybatis-3-cofig.dtd";
    private static final String MYBATIS_MAPPER_SYSTEM="mybatis-3-mybatis.dtd";
    private static final String MYBATIS_CONFIG_DTD="org/apache/ibatis/builder/xml/mybatis-3-cofig.dtd";
    private static final String MYBATIS_MAPPER_DTD="org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd";
    @Override
    public InputSource resolveEntity(String publicId, String systemId) throws SAXException, IOException {
        if(systemId!=null){
            String lowerCaseSystemId=systemId.toLowerCase(Locale.ENGLISH);
            if(lowerCaseSystemId.contains(MYBATIS_CONFIG_SYSTEM) || lowerCaseSystemId.contains(IBATIS_CONFIG_SYSTEM)){
              return getInputSource(MYBATIS_CONFIG_DTD,publicId,systemId);
            }else if(lowerCaseSystemId.contains(MYBATIS_MAPPER_SYSTEM) || lowerCaseSystemId.contains(IBATIS_MAPPER_SYSTEM)){
                return getInputSource(MYBATIS_MAPPER_DTD,publicId,systemId);
            }

        }
        return null;
    }

    public InputSource getInputSource(String path,String publicId,String systemId){
        InputSource source=null;
        try {
            InputStream in= Resources.getResourceAsStream(path);
            source=new InputSource(in);
            source.setPublicId(publicId);
            source.setSystemId(systemId);
        }catch (Exception e){
            e.printStackTrace();
        }
        return source;
    }
}
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