摘要：三大巨頭結(jié)果集再通過(guò)反射機(jī)制映射到對(duì)象上面，便做好了數(shù)據(jù)的映射關(guān)于映射具體內(nèi)容可查閱資料及源碼到這我們已經(jīng)完成了一個(gè)簡(jiǎn)易的框架了通過(guò)手寫(xiě)一個(gè)簡(jiǎn)單的框架，我們就可以看得懂源碼了，學(xué)習(xí)框架設(shè)計(jì)的思路并且增強(qiáng)我們的內(nèi)功

1.創(chuàng)建SqlSessionFactory實(shí)例.

2.實(shí)例化過(guò)程中，加載配置文件創(chuàng)建configuration對(duì)象.

3.通過(guò)factory創(chuàng)建SqlSession對(duì)象,把configuaration傳入SqlSession.

4.通過(guò)SqlSession獲取mapper接口動(dòng)態(tài)代理

5.通過(guò)代理對(duì)調(diào)sqlsession中查詢(xún)方法;

6.sqlsession將查詢(xún)方法轉(zhuǎn)發(fā)給executor;

7.executor基于JDBC訪問(wèn)數(shù)據(jù)庫(kù)獲取數(shù)據(jù);

8.executor通過(guò)反射將數(shù)據(jù)轉(zhuǎn)換成POJO并返回給sqlsession;

9.數(shù)據(jù)返回給調(diào)用者

上節(jié)講到快速入門(mén)mybatis的demo三大階段

// 1.讀取mybatis配置文件創(chuàng)SqlSessionFactory
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
inputStream.close();
//-------------第二階段-------------
// 2.獲取sqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
// 3.獲取對(duì)應(yīng)mapper
TUserMapper mapper = sqlSession.getMapper(TUserMapper.class);

//-------------第三階段-------------
// 4.執(zhí)行查詢(xún)語(yǔ)句并返回結(jié)果
TUser user = mapper.selectByPrimaryKey(1);
System.out.println(user.toString());

第一階段先把配置文件加載到內(nèi)存，包括數(shù)據(jù)庫(kù)信息和mapper.xml。

針對(duì)mapper.xml我們定義一個(gè)MappedStatement類(lèi)來(lái)存入相應(yīng)信息.

public class MappedStatement {
    //此處忽略getset方法
    private String namespace;//xml里面的namespace即mapper接口路徑
    
    private String sourceId;//mapper接口路徑+xml里面的每一個(gè)id
    
    private String sql;//sql語(yǔ)句
    
    private String resultType;//返回類(lèi)型    

}

再定義一個(gè)全局配置信息即Configuration存放所有配置信息：

public class Configuration {
    //記錄mapper xml文件存放的位置
    public static final String MAPPER_CONFIG_LOCATION = "config";
    //記錄數(shù)據(jù)庫(kù)連接信息文件存放位置
    public static final String DB_CONFIG_FILE = "db.properties";
    
    private String dbUrl;

    private String dbUserName;

    private String dbPassword;

    private String dbDriver;

    //mapper xml解析完以后select節(jié)點(diǎn)的信息存放在mappedStatements,key為MappedStatement里面 
     //的sourceId
    protected final Map mappedStatements = new HashMap();
    
    //為mapper接口生成動(dòng)態(tài)代理的方法
public  T getMapper(Class type, SqlSession sqlSession) {
    return MapperProxyFactory.getMapperProxy(sqlSession, type);
}
}

SqlSessionFactory實(shí)例化，并加載configuaration對(duì)象信息,這樣就把所有的配置信息加載到內(nèi)存里

public class SqlSessionFactory {
    //配置對(duì)象全局唯一 加載數(shù)據(jù)庫(kù)信息和mapper文件信息
    private Configuration conf = new Configuration();

    public SqlSessionFactory() {
        //加載數(shù)據(jù)庫(kù)信息
         loadDbInfo();
         //加載mapper文件信息
         loadMappersInfo();
    }
    
    private void loadMappersInfo() {
        URL resources =null;
        resources = SqlSessionFactory.class.getClassLoader().getResource(conf.MAPPER_CONFIG_LOCATION);
        File mappers = new File(resources.getFile());
        if(mappers.isDirectory()){
            File[] listFiles = mappers.listFiles();
            for (File file : listFiles) {
                loadMapperInfo(file);
            }
        }
    }

    private void loadMapperInfo(File file) {
        // 創(chuàng)建saxReader對(duì)象  
        SAXReader reader = new SAXReader();  
        // 通過(guò)read方法讀取一個(gè)文件 轉(zhuǎn)換成Document對(duì)象  
        Document document=null;
        try {
            document = reader.read(file);
        } catch (DocumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }  
        //獲取根節(jié)點(diǎn)元素對(duì)象  
        Element node = document.getRootElement();
        //獲取命名空間
        String namespace = node.attribute("namespace").getData().toString();
        //獲取select子節(jié)點(diǎn)列表
        List selects = node.elements("select");
        for (Element element : selects) {//遍歷select節(jié)點(diǎn)，將信息記錄到MappedStatement對(duì)象，并登記到configuration對(duì)象中
            MappedStatement mappedStatement = new MappedStatement();
            String id = element.attribute("id").getData().toString();
            String resultType = element.attribute("resultType").getData().toString();
            String sql = element.getData().toString();
            String sourceId = namespace+"."+id;
            mappedStatement.setSourceId(sourceId);
            mappedStatement.setResultType(resultType);
            mappedStatement.setSql(sql);
            mappedStatement.setNamespace(namespace);
            conf.getMappedStatements().put(sourceId, mappedStatement);//登記到configuration對(duì)象中
        }
    }

    private void loadDbInfo() {
        InputStream dbIn = SqlSessionFactory.class.getClassLoader().getResourceAsStream(conf.DB_CONFIG_FILE);
         Properties p = new Properties();
         try {
            p.load(dbIn);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
         conf.setDbDriver(p.get("jdbc.driver").toString());
         conf.setDbPassword(p.get("jdbc.password").toString());
         conf.setDbUrl(p.get("jdbc.url").toString());
         conf.setDbUserName(p.get("jdbc.username").toString());
    }
    public SqlSession openSession(){
        SqlSession sqlSession  = new DefaultSqlSession(conf);
        return sqlSession;
    }
}

第二階段為獲取Sqlsession并且從sqlsession獲取mapper動(dòng)態(tài)代理.

Sqlsession

mybatis暴露給外部的接口，實(shí)現(xiàn)增刪改查的能力

1.對(duì)外提供數(shù)據(jù)訪問(wèn)的api

2.對(duì)內(nèi)將請(qǐng)求轉(zhuǎn)發(fā)給executor

3.executor基于JDBC訪問(wèn)數(shù)據(jù)庫(kù)

public class DefaultSqlSession implements SqlSession {
       
       //配置對(duì)象全局唯一 加載數(shù)據(jù)庫(kù)信息和mapper文件信息
       private Configuration conf;
       
       //真正提供數(shù)據(jù)庫(kù)訪問(wèn)能力的對(duì)象
       private Executor executor;
       
   
       public DefaultSqlSession(Configuration conf) {
           super();
           this.conf = conf;
           executor = new SimpleExecutor(conf);
       }
   
       public  T selectOne(String statement, Object parameter) {
           List