深入理解Mybatis（第一讲）——手写ORM框架（简易版Mybatis）

﹏ヽ暗。殇╰゛Y 2023-02-14 06:49 25阅读 0赞

我们来自定义一个持久层框架，也就是Mybatis的简易版。

#### 使用端的搭建 ####

idea中新建maven工程IPersistence\_test：  
![format_png][]  
在resources目录下新建sqlMapConfig.xml文件，

##### 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实体类： #####

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 + '\'' +
                    '}';
        }
    }

使用端暂时就搭建完成。

#### 持久层框架端的搭建 ####

下面我们来搭建持久层框架：  
新建一个module,maven项目：IPersistence  
pom.xml中引入一下依赖

<dependencies>
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.44</version>
            </dependency>
            
            <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>
            
            <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>

创建一个Configuration类,主要是存放从sqlMapConfig.xml和Usermapper.xml配置文件中解析出来的一些元素和内容，用来一层层向下传递：

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解析出来的内容 */
    public class Configuration { 
        //存放数据库配置信息，从sqlMapConfig.xml中解析出来
        private DataSource dataSource;
    
        //存放Mapper.xml中解析出来的内容，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 封装的是数据库信息，Configuration中封装了一个对象MappedStatement:

package com.lagou.pojo;
    
    /** * @author liuyj * @Title: MappedStatement * @create 2020-05-27 15:13 * @ProjectName IPersistence * @Description: 存放UserMapper.xml解析出来的内容 */
    public class MappedStatement { 
        //id标识
        private String id;
    
        //返回值类型
        private String resultType;
    
        //传入参数类型
        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;
        }
    }

主要是用来存储从映射配置文件中解析出来的sql查询标签的id及传入参数、返回结果类型、查询的sql等，其中Mapper.xml中每一个标签，  
比如：

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

都会封装成一个MappedStatement对象,然后所有的MappedStatement对象都被存储到Configuration类中的Map集合mappedStatementMap当中去，Map集合中的key是statementId（statementId由两部分组成，一是Mapper.xml中的namespace，二是每一个标签中的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： #####

主要用来读取xml文件，作为一个字节流存储在内存中：

package com.lagou.io;
    
    import java.io.InputStream;
    
    /** * @author liuyj * @Title: * @create 2020-05-27 14:48 * @ProjectName IPersistence * @Description: TODO */
    public class Resources { 
    
    
        //根据配置文件的路径，将配置文件加载成字节输入流，存储在内存中
        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，将解析出来的内容封装到configuration中
            XMLConfigBuilder xmlConfigBuilder=new XMLConfigBuilder();
            Configuration configuration = xmlConfigBuilder.parseConfig(in);
    
            //第二：创建sqlSessionFactory对象:工厂类：生产sqlSession:会话对象
            DefaultSqlSessionFactory defaultSqlSessionFactory=new DefaultSqlSessionFactory(configuration);
            return defaultSqlSessionFactory;
        }
    }

##### XMLConfigBuilder : #####

使用dom4j解析sqlMapConfig.xml文件，并调用XMLMapperBuilder 中的方法解析Mapper.xml映射文件，将结果封装在Configuration对象中：

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();
        }
    
        /** * *该方法就是使用dom4j将配置文件解析，封装为Configuration */
        public Configuration parseConfig(InputStream inputStream) throws DocumentException, PropertyVetoException { 
    
            Document document = new SAXReader().read(inputStream);
            //<Configuration>标签
            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里面的mapper标签，
            // 解析mapper.xml：拿到路径--字节输入流--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 : #####

用来解析映射配置文件Mapper.xml中的内容：

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及实现类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 { 
    
        //查询所有
        public <E> List<E> selectList(String statementid, Object... params) throws Exception;
    
        //根据条件查询单个
        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 { 
    
            //将要去完成对simpleExecutor里的query方法的调用
            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("查询结果为空或者返回结果过多");
            }
    
        }
        }

##### SqlSession实现类中调用的Executor及其实现类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 { 
            //注册驱动，获取数据库连接
            Connection connection = configuration.getDataSource().getConnection();
            //获取sql语句：select * from user where id=#{id} and username=#{username}
            //转换sql：select * from user where id=？ and username=？，同时需要对#{}里面的值进行解析存储
            String sql = mappedStatement.getSql();
            BoundSql boundSql=getBoundSql(sql);
            //获取预处理对象preparedStatement
            PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());
    
            //设置参数
              //获取到了参数的全路径
            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);
                //暴力访问
                declaredField.setAccessible(true);
                Object o = declaredField.get(params[0]);
                preparedStatement.setObject(i+1,o);
            }
            //执行sql
            ResultSet resultSet = preparedStatement.executeQuery();
            String resultType = mappedStatement.getResultType();
            Class<?> resultTypeClass = getClassType(resultType);
            ArrayList<Object> objects = new ArrayList<Object>();
    
    
            //封装返回结果集
            while (resultSet.next()) { 
                Object o = resultTypeClass.newInstance();
                //元数据
                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);
    
                    //使用反射或者内省，根据数据库表和实体的对应关系，完成封装
                    PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                    Method writeMethod = propertyDescriptor.getWriteMethod();
                    writeMethod.invoke(o,value);
                }
                objects.add(o);
            }
    
            return (List<E>) objects;
        }
    
        /** * 完成对#{}的解析工作：1.将#{}使用？代替 ，2.解析出#{}里面的值进行存储 * @param sql * @return */
        private BoundSql getBoundSql(String sql) { 
            //标记处理类：配置标记解析器GenericTokenParser来完成对配置文件的解析工作，其中TokenHandler主要完成处理
            ParameterMappingTokenHandler parameterMappingTokenHandler=new ParameterMappingTokenHandler();
    
    //GenericTokenParser：通用的标记解析器，完成了对代码中占位符的解析，然后再根据给定的标记处理器（TokenHandler）来进行表达式的处理
    //三个参数：分别为openToken(开始标记)、closeToken（结束标记）、handler(标记处理器)
    
            GenericTokenParser genericTokenParser=new GenericTokenParser("#{","}",parameterMappingTokenHandler);
    
            //解析出来的sql
            String parseSql = genericTokenParser.parse(sql);
            //从#{}里面解析出来的参数名称
            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 中使用的几个标记解析器，也附录一下吧，是从mybatis源码中直接拿来用的：

###### GenericTokenParser ######

package com.lagou.utils;
    
    /** * @author Clinton Begin */
    public class GenericTokenParser { 
    
      private final String openToken; //开始标记
      private final String closeToken; //结束标记
      private final TokenHandler handler; //标记处理器
    
      public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) { 
        this.openToken = openToken;
        this.closeToken = closeToken;
        this.handler = handler;
      }
    
      /** * 解析${}和#{} * @param text * @return * 该方法主要实现了配置文件、脚本等片段中占位符的解析、处理工作，并返回最终需要的数据。 * 其中，解析工作由该方法完成，处理工作是由处理器handler的handleToken()方法来实现 */
      public String parse(String text) { 
        // 验证参数问题，如果是null，就返回空字符串。
        if (text == null || text.length()==0) { 
          return "";
        }
    
        // 下面继续验证是否包含开始标签，如果不包含，默认不是占位符，直接原样返回即可，否则继续执行。
        int start = text.indexOf(openToken, 0);
        if (start == -1) { 
          return text;
        }
    
       // 把text转成字符数组src，并且定义默认偏移量offset=0、存储最终需要返回字符串的变量builder，
        // text变量中占位符对应的变量名expression。判断start是否大于-1(即text中是否存在openToken)，如果存在就执行下面代码
        char[] src = text.toCharArray();
        int offset = 0;
        final StringBuilder builder = new StringBuilder();
        StringBuilder expression = null;
        while (start > -1) { 
         // 判断如果开始标记前如果有转义字符，就不作为openToken进行处理，否则继续处理
          if (start > 0 && src[start - 1] == '\\') { 
            builder.append(src, offset, start - offset - 1).append(openToken);
            offset = start + openToken.length();
          } else { 
            //重置expression变量，避免空指针或者老数据干扰。
            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) { 存在结束标记时
              if (end > offset && src[end - 1] == '\\') { //如果结束标记前面有转义字符时
                // 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 { //不存在转义字符，即需要作为参数进行处理
                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 { 
              //首先根据参数的key（即expression）进行参数处理，返回?作为占位符
              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是参数名称 #{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);
    }

#### 测试使用： ####

先生成jar包，执行mvn install命令。  
mvn install  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl_size_16_color_FFFFFF_t_70]  
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>

数据库建表：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl_size_16_color_FFFFFF_t_70 1]  
![在这里插入图片描述][20200601161457397.png]

测试：

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 { 
    
            //调用
            User user=new User();
            user.setId(1);
            user.setUsername("张三");
            User user2 = sqlSession.selectOne("user.selectOne", user);
            System.out.println(user2);
    
        }
    }

运行结果：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl_size_16_color_FFFFFF_t_70 2]  
大功告成。  
下节我们来讲对于我们这个框架的一个优化。

[format_png]: https://imgconvert.csdnimg.cn/aHR0cHM6Ly9pbWcyMDIwLmNuYmxvZ3MuY29tL2Jsb2cvMTIzMDAwMy8yMDIwMDYvMTIzMDAwMy0yMDIwMDYwMTE1MDUwOTkyNi0xNDkwMDA5NDgucG5n?x-oss-process=image/format,png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/2020060116071550.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200601161031211.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl,size_16,color_FFFFFF,t_70
[20200601161457397.png]: https://img-blog.csdnimg.cn/20200601161457397.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20200601161849960.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lvbmdidXRpbmd4aWRl,size_16,color_FFFFFF,t_70