深入理解Mybatis（第一講）——手寫ORM框架（簡易版Mybatis）

我們來自定義一個持久層框架，也就是Mybatis的簡易版。

使用端的搭建

idea中新建maven工程IPersistence_test：

在resources目錄下新建sqlMapConfig.xml文件，

<Configuration>
    <dataSource>
        <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
        <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/lagou?useUnicode=true&amp;characterEncoding=utf8&amp;zeroDateTimeBehavior=convertToNull&amp;useSSL=false"></property>
        <property name="user" value="root"></property>
        <property name="password" value="000"></property>
    </dataSource>

    <mapper resource="UserMapper.xml"></mapper>

</Configuration>

UserMapper.xml:

<mapper namespace="user">
<select id="selectOne" paramterType="com.lagou.pojo.User"
resultType="com.lagou.pojo.User">
select * from user where id = #{id} and username =#{username}
</select>
<select id="selectList" resultType="com.lagou.pojo.User">
select * from user
</select>
</mapper>

User實體類：

package com.lagou.test;

/**
 * @author liuyj
 * @Title: User
 * @create 2020-05-29 15:06
 * @ProjectName lagou_project
 * @Description: TODO
 */
public class User {
    private Integer id;
    private String username;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                '}';
    }
}

使用端暫時就搭建完成。

持久層框架端的搭建

下面我們來搭建持久層框架：
新建一個module,maven項目：IPersistence
pom.xml中引入一下依賴

<dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.44</version>
        </dependency>
        <!-- 連接池-->
        <dependency>
            <groupId>c3p0</groupId>
            <artifactId>c3p0</artifactId>
            <version>0.9.1.2</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.12</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
        </dependency>
        <!-- 解析xml文件-->
        <dependency>
            <groupId>dom4j</groupId>
            <artifactId>dom4j</artifactId>
            <version>1.6.1</version>
        </dependency>
        <dependency>
            <groupId>jaxen</groupId>
            <artifactId>jaxen</artifactId>
            <version>1.1.6</version>
        </dependency>
    </dependencies>

創建一個Configuration類,主要是存放從sqlMapConfig.xml和Usermapper.xml配置文件中解析出來的一些元素和內容，用來一層層向下傳遞：

package com.lagou.pojo;

import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;

/**
 * @author liuyj
 * @Title: Configuration
 * @create 2020-05-27 15:20
 * @ProjectName IPersistence
 * @Description:  存放sqlMapConfig.xml解析出來的內容
 */
public class Configuration {
    //存放數據庫配置信息，從sqlMapConfig.xml中解析出來
    private DataSource dataSource;

    //存放Mapper.xml中解析出來的內容，key是statementId
    private Map<String,MappedStatement> mappedStatementMap=new HashMap<String, MappedStatement>();

    public DataSource getDataSource() {
        return dataSource;
    }

    public void setDataSource(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    public Map<String, MappedStatement> getMappedStatementMap() {
        return mappedStatementMap;
    }

    public void setMappedStatementMap(Map<String, MappedStatement> mappedStatementMap) {
        this.mappedStatementMap = mappedStatementMap;
    }
}

其中DataSource 封裝的是數據庫信息，Configuration中封裝了一個對象MappedStatement:

package com.lagou.pojo;

/**
 * @author liuyj
 * @Title: MappedStatement
 * @create 2020-05-27 15:13
 * @ProjectName IPersistence
 * @Description: 存放UserMapper.xml解析出來的內容
 */
public class MappedStatement {
    //id標識
    private String id;

    //返回值類型
    private String resultType;

    //傳入參數類型
    private String paramenterType;

    //sql
    private String sql;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getResultType() {
        return resultType;
    }

    public void setResultType(String resultType) {
        this.resultType = resultType;
    }

    public String getParamenterType() {
        return paramenterType;
    }

    public void setParamenterType(String paramenterType) {
        this.paramenterType = paramenterType;
    }

    public String getSql() {
        return sql;
    }

    public void setSql(String sql) {
        this.sql = sql;
    }
}

主要是用來存儲從映射配置文件中解析出來的sql查詢標籤的id及傳入參數、返回結果類型、查詢的sql等，其中Mapper.xml中每一個標籤，
比如：

<select id="selectList" resultType="com.lagou.pojo.User">
select * from user
</select>

都會封裝成一個MappedStatement對象,然後所有的MappedStatement對象都被存儲到Configuration類中的Map集合mappedStatementMap當中去，Map集合中的key是statementId（statementId由兩部分組成，一是Mapper.xml中的namespace，二是每一個標籤中的id，比如UserMapper.xml中的selectOne，在Configuration中map集合中的key值就是user.selectOne）。

Resource文件：

主要用來讀取xml文件，作爲一個字節流存儲在內存中：

package com.lagou.io;

import java.io.InputStream;

/**
 * @author liuyj
 * @Title:
 * @create 2020-05-27 14:48
 * @ProjectName IPersistence
 * @Description: TODO
 */
public class Resources {


    //根據配置文件的路徑，將配置文件加載成字節輸入流，存儲在內存中
    public static InputStream getResourceAsStream(String path){

        InputStream resourceStream= Resources.class.getClassLoader().getResourceAsStream(path);
        return resourceStream;
    }
}

SqlSessionFactoryBuilder:

package com.lagou.sqlSession;

import com.lagou.config.XMLConfigBuilder;
import com.lagou.pojo.Configuration;
import org.dom4j.DocumentException;

import java.beans.PropertyVetoException;
import java.io.InputStream;

/**
 * @author liuyj
 * @Title: SqlSessionFactoryBuilder
 * @create 2020-05-27 15:37
 * @ProjectName IPersistence
 * @Description: TODO
 */
public class SqlSessionFactoryBuilder {

    public SqlSessionFactory build(InputStream in) throws DocumentException, PropertyVetoException {

        //第一，使用dom4j解析配置文件，將解析出來的內容封裝到configuration中
        XMLConfigBuilder xmlConfigBuilder=new XMLConfigBuilder();
        Configuration configuration = xmlConfigBuilder.parseConfig(in);

        //第二：創建sqlSessionFactory對象:工廠類：生產sqlSession:會話對象
        DefaultSqlSessionFactory defaultSqlSessionFactory=new DefaultSqlSessionFactory(configuration);
        return defaultSqlSessionFactory;
    }
}

XMLConfigBuilder :

使用dom4j解析sqlMapConfig.xml文件，並調用XMLMapperBuilder 中的方法解析Mapper.xml映射文件，將結果封裝在Configuration對象中：

package com.lagou.config;

import com.lagou.io.Resources;
import com.lagou.pojo.Configuration;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

import java.beans.PropertyVetoException;
import java.io.InputStream;
import java.util.List;
import java.util.Properties;

/**
 * @author liuyj
 * @Title: XMLConfigBuilder
 * @create 2020-05-27 15:39
 * @ProjectName IPersistence
 * @Description: TODO
 */
public class XMLConfigBuilder {

    private Configuration configuration;
    public XMLConfigBuilder(){
        this.configuration=new Configuration();
    }

    /**
     *
     *該方法就是使用dom4j將配置文件解析，封裝爲Configuration
     */
    public Configuration parseConfig(InputStream inputStream) throws DocumentException, PropertyVetoException {

        Document document = new SAXReader().read(inputStream);
        //<Configuration>標籤
        Element rootElement = document.getRootElement();
        List<Element> list = rootElement.selectNodes("//property");
        Properties properties=new Properties();
        for (Element element : list) {
            String name = element.attributeValue("name");
            String value = element.attributeValue("value");
            properties.setProperty(name,value);
        }

        ComboPooledDataSource comboPooledDataSource=new ComboPooledDataSource();
        comboPooledDataSource.setDriverClass(properties.getProperty("driverClass"));
        comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl"));
        comboPooledDataSource.setUser(properties.getProperty("user"));
        comboPooledDataSource.setPassword(properties.getProperty("password"));

        configuration.setDataSource(comboPooledDataSource);

        //解析sqlMapConfig.xml裏面的mapper標籤，
        // 解析mapper.xml：拿到路徑--字節輸入流--dom4j解析
        List<Element> mapperList = rootElement.selectNodes("//mapper");
        for (Element element : mapperList) {
            String mapperPath = element.attributeValue("resource");
            InputStream resourceAsStream = Resources.getResourceAsStream(mapperPath);
            XMLMapperBuilder xmlMaperBuilder=new XMLMapperBuilder(configuration);
            xmlMaperBuilder.parse(resourceAsStream);
        }
        return configuration;
    }
}

XMLMapperBuilder :

用來解析映射配置文件Mapper.xml中的內容：

package com.lagou.config;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

import java.io.InputStream;
import java.util.List;

/**
 * @author liuyj
 * @Title: XMLMapperBuilder
 * @create 2020-05-28 10:59
 * @ProjectName lagou_project
 * @Description: 解析mapper.xml文件
 */
public class XMLMapperBuilder {
    private Configuration configuration;
    public XMLMapperBuilder(Configuration configuration) {
        this.configuration=configuration;
    }

    public void parse(InputStream inputStream) throws DocumentException {
        Document document = new SAXReader().read(inputStream);
        Element rootElement = document.getRootElement();
        String namespace = rootElement.attributeValue("namespace");
        List<Element> list = rootElement.selectNodes("//select");
        for (Element element : list) {

            String id = element.attributeValue("id");
            String parameterType = element.attributeValue("parameterType");
            String resultType = element.attributeValue("resultType");
            String sqlText = element.getTextTrim();

            String key=namespace+"."+id;
            MappedStatement mappedStatement=new MappedStatement();
            mappedStatement.setId(id);
            mappedStatement.setParamenterType(parameterType);
            mappedStatement.setResultType(resultType);
            mappedStatement.setSql(sqlText);
            configuration.getMappedStatementMap().put(key,mappedStatement);
        }

    }
}

package com.lagou.sqlSession;

/**
 * @author liuyj
 * @Title: SqlSessionFactory
 * @create 2020-05-27 15:38
 * @ProjectName IPersistence
 * @Description: TODO
 */
public interface SqlSessionFactory {
    SqlSession openSession();
}

package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;

/**
 * @author liuyj
 * @Title: DefaultSqlSessionFactory
 * @create 2020-05-28 11:38
 * @ProjectName lagou_project
 * @Description: TODO
 */
public class DefaultSqlSessionFactory implements SqlSessionFactory{

    private Configuration configuration;

    public DefaultSqlSessionFactory(Configuration configuration) {
        this.configuration = configuration;
    }

    public SqlSession openSession() {
        return new DefaultSqlSession(configuration);
    }
}

SqlSession及實現類DefaultSqlSession:

package com.lagou.sqlSession;

import java.util.List;

/**
 * @author liuyj
 * @Title: SqlSession
 * @create 2020-05-28 11:56
 * @ProjectName lagou_project
 * @Description: TODO
 */
public interface SqlSession {

    //查詢所有
    public <E> List<E> selectList(String statementid, Object... params) throws Exception;

    //根據條件查詢單個
    public <T> T selectOne(String statementid,Object... params) throws Exception;
    }

package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

/**
 * @author liuyj
 * @Title: DefaultSqlSession
 * @create 2020-05-28 11:57
 * @ProjectName lagou_project
 * @Description: TODO
 */
public class DefaultSqlSession implements SqlSession {
    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    public <E> List<E> selectList(String statementid, Object... params) throws Exception {

        //將要去完成對simpleExecutor裏的query方法的調用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if(objects.size()==1){
            return (T) objects.get(0);
        }else {
            throw new RuntimeException("查詢結果爲空或者返回結果過多");
        }

    }
    }

SqlSession實現類中調用的Executor及其實現類SimpleExecutor ：

package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.util.List;

/**
 * @author lyj
 * @Title: Executor
 * @ProjectName lagou_project
 * @Description: TODO
 * @date 2020/5/28 22:00
 */

public interface Executor {
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception;
}

package com.lagou.sqlSession;


import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import com.lagou.utils.GenericTokenParser;
import com.lagou.utils.ParameterMapping;
import com.lagou.utils.ParameterMappingTokenHandler;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * @author lyj
 * @Title: SimpleExecutor
 * @ProjectName lagou_project
 * @Description: TODO
 * @date 2020/5/28 21:59
 */

public class SimpleExecutor implements Executor {

    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        //註冊驅動，獲取數據庫連接
        Connection connection = configuration.getDataSource().getConnection();
        //獲取sql語句：select * from user where id=#{id} and username=#{username}
        //轉換sql：select * from user where id=？ and username=？，同時需要對#{}裏面的值進行解析存儲
        String sql = mappedStatement.getSql();
        BoundSql boundSql=getBoundSql(sql);
        //獲取預處理對象preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        //設置參數
          //獲取到了參數的全路徑
        String paramenterType = mappedStatement.getParamenterType();
        Class<?> parametertypeClass=getClassType(paramenterType);

        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String content = parameterMapping.getContent();
            //反射
            Field declaredField = parametertypeClass.getDeclaredField(content);
            //暴力訪問
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[0]);
            preparedStatement.setObject(i+1,o);
        }
        //執行sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);
        ArrayList<Object> objects = new ArrayList<Object>();


        //封裝返回結果集
        while (resultSet.next()) {
            Object o = resultTypeClass.newInstance();
            //元數據
            ResultSetMetaData metaData = resultSet.getMetaData();
            for (int i = 1; i <= metaData.getColumnCount(); i++) {
                //字段名
                String columnName = metaData.getColumnName(i);
                //字段值
                Object value = resultSet.getObject(columnName);

                //使用反射或者內省，根據數據庫表和實體的對應關係，完成封裝
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();
                writeMethod.invoke(o,value);
            }
            objects.add(o);
        }

        return (List<E>) objects;
    }

    /**
     * 完成對#{}的解析工作：1.將#{}使用？代替 ，2.解析出#{}裏面的值進行存儲
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {
        //標記處理類：配置標記解析器GenericTokenParser來完成對配置文件的解析工作，其中TokenHandler主要完成處理
        ParameterMappingTokenHandler parameterMappingTokenHandler=new ParameterMappingTokenHandler();

//GenericTokenParser：通用的標記解析器，完成了對代碼中佔位符的解析，然後再根據給定的標記處理器（TokenHandler）來進行表達式的處理
//三個參數：分別爲openToken(開始標記)、closeToken（結束標記）、handler(標記處理器)

        GenericTokenParser genericTokenParser=new GenericTokenParser("#{","}",parameterMappingTokenHandler);

        //解析出來的sql
        String parseSql = genericTokenParser.parse(sql);
        //從#{}裏面解析出來的參數名稱
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();
        BoundSql boundSql=new BoundSql(parseSql,parameterMappings);

        return boundSql;

    }
    }

BoundSql ：

package com.lagou.sqlSession;
import com.lagou.utils.ParameterMapping;

import java.util.ArrayList;
import java.util.List;

/**
* @author lyj
* @Title: BoundSql
* @ProjectName lagou_project
* @Description: TODO
* @date 2020/5/28 22:03
*/

public class BoundSql {
   private String sqlText;
   private List<ParameterMapping>parameterMappingList=new ArrayList<ParameterMapping>();

   public BoundSql(String sqlText, List<ParameterMapping> parameterMappingList) {
       this.sqlText = sqlText;
       this.parameterMappingList = parameterMappingList;
   }

   public String getSqlText() {
       return sqlText;
   }

   public void setSqlText(String sqlText) {
       this.sqlText = sqlText;
   }

   public List<ParameterMapping> getParameterMappingList() {
       return parameterMappingList;
   }

   public void setParameterMappingList(List<ParameterMapping> parameterMappingList) {
       this.parameterMappingList = parameterMappingList;
   }
}

SimpleExecutor 中使用的幾個標記解析器，也附錄一下吧，是從mybatis源碼中直接拿來用的：

GenericTokenParser

package com.lagou.utils;

/**
 * @author Clinton Begin
 */
public class GenericTokenParser {

  private final String openToken; //開始標記
  private final String closeToken; //結束標記
  private final TokenHandler handler; //標記處理器

  public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) {
    this.openToken = openToken;
    this.closeToken = closeToken;
    this.handler = handler;
  }

  /**
   * 解析${}和#{}
   * @param text
   * @return
   * 該方法主要實現了配置文件、腳本等片段中佔位符的解析、處理工作，並返回最終需要的數據。
   * 其中，解析工作由該方法完成，處理工作是由處理器handler的handleToken()方法來實現
   */
  public String parse(String text) {
    // 驗證參數問題，如果是null，就返回空字符串。
    if (text == null || text.length()==0) {
      return "";
    }

    // 下面繼續驗證是否包含開始標籤，如果不包含，默認不是佔位符，直接原樣返回即可，否則繼續執行。
    int start = text.indexOf(openToken, 0);
    if (start == -1) {
      return text;
    }

   // 把text轉成字符數組src，並且定義默認偏移量offset=0、存儲最終需要返回字符串的變量builder，
    // text變量中佔位符對應的變量名expression。判斷start是否大於-1(即text中是否存在openToken)，如果存在就執行下面代碼
    char[] src = text.toCharArray();
    int offset = 0;
    final StringBuilder builder = new StringBuilder();
    StringBuilder expression = null;
    while (start > -1) {
     // 判斷如果開始標記前如果有轉義字符，就不作爲openToken進行處理，否則繼續處理
      if (start > 0 && src[start - 1] == '\\') {
        builder.append(src, offset, start - offset - 1).append(openToken);
        offset = start + openToken.length();
      } else {
        //重置expression變量，避免空指針或者老數據干擾。
        if (expression == null) {
          expression = new StringBuilder();
        } else {
          expression.setLength(0);
        }
        builder.append(src, offset, start - offset);
        offset = start + openToken.length();
        int end = text.indexOf(closeToken, offset);
        while (end > -1) {////存在結束標記時
          if (end > offset && src[end - 1] == '\\') {//如果結束標記前面有轉義字符時
            // this close token is escaped. remove the backslash and continue.
            expression.append(src, offset, end - offset - 1).append(closeToken);
            offset = end + closeToken.length();
            end = text.indexOf(closeToken, offset);
          } else {//不存在轉義字符，即需要作爲參數進行處理
            expression.append(src, offset, end - offset);
            offset = end + closeToken.length();
            break;
          }
        }
        if (end == -1) {
          // close token was not found.
          builder.append(src, start, src.length - start);
          offset = src.length;
        } else {
          //首先根據參數的key（即expression）進行參數處理，返回?作爲佔位符
          builder.append(handler.handleToken(expression.toString()));
          offset = end + closeToken.length();
        }
      }
      start = text.indexOf(openToken, offset);
    }
    if (offset < src.length) {
      builder.append(src, offset, src.length - offset);
    }
    return builder.toString();
  }
}

ParameterMapping:

package com.lagou.utils;

public class ParameterMapping {

    private String content;

    public ParameterMapping(String content) {
        this.content = content;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}

ParameterMappingTokenHandler:

package com.lagou.utils;

import java.util.ArrayList;
import java.util.List;




public class ParameterMappingTokenHandler implements TokenHandler {
	private List<ParameterMapping> parameterMappings = new ArrayList<ParameterMapping>();

	// context是參數名稱 #{id} #{username}

	public String handleToken(String content) {
		parameterMappings.add(buildParameterMapping(content));
		return "?";
	}

	private ParameterMapping buildParameterMapping(String content) {
		ParameterMapping parameterMapping = new ParameterMapping(content);
		return parameterMapping;
	}

	public List<ParameterMapping> getParameterMappings() {
		return parameterMappings;
	}

	public void setParameterMappings(List<ParameterMapping> parameterMappings) {
		this.parameterMappings = parameterMappings;
	}

}

package com.lagou.utils;

/**
 * @author Clinton Begin
 */
public interface TokenHandler {
  String handleToken(String content);
}

測試使用：

先生成jar包，執行mvn install命令。
mvn install

在使用端IPersistence_test中引入jar包：

  <dependency>
            <groupId>com.lagou</groupId>
            <artifactId>IPersistence</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>

數據庫建表：

測試：

package com.lagou.test;

import com.lagou.dao.IUserDao;
import com.lagou.io.Resources;
import com.lagou.sqlSession.SqlSession;
import com.lagou.sqlSession.SqlSessionFactory;
import com.lagou.sqlSession.SqlSessionFactoryBuilder;
import org.dom4j.DocumentException;
import org.junit.Before;
import org.junit.Test;

import java.beans.PropertyVetoException;
import java.io.InputStream;

/**
 * @author liuyj
 * @Title: IPersistenctTest
 * @create 2020-05-27 15:08
 * @ProjectName IPersistence
 * @Description: TODO
 */
public class IPersistenctTest {

      private  SqlSession sqlSession;
    @Before
    public void before() throws PropertyVetoException, DocumentException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");

        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);

         sqlSession = sqlSessionFactory.openSession();
    }
    @Test
    public void test() throws Exception {

        //調用
        User user=new User();
        user.setId(1);
        user.setUsername("張三");
        User user2 = sqlSession.selectOne("user.selectOne", user);
        System.out.println(user2);

    }
}

運行結果：

大功告成。
下節我們來講對於我們這個框架的一個優化。