MyBatis原理分析手写持久层框架2-阿里云开发者社区

4 自定义持久层框架_编码

  <properties>
        <!-- Encoding -->
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <maven.compiler.encoding>UTF-8</maven.compiler.encoding>
        <java.version>11</java.version>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>

  <!--引入ipersistent的依赖-->

在使用端项目中创建配置配置文件

创建 sqlMapConfig.xml

<configuration> 
    <!--1.配置数据库配置信息-->
    <dataSource>
        <property name="driverClassName" value="com.mysql.jdbc.Driver"></property>
        <property name="url" value="jdbc:mysql:///zdy_mybatis?useSSL=false&amp;characterEncoding=UTF-8&amp;serverTimezone=UTC"></property>
        <property name="username" value="root"></property>
        <property name="password" value="root"></property>
    </dataSource>


    <!--2.引入映射配置文件-->
    <mappers>
        <mapper resource="mapper/UserMapper.xml"></mapper>
    </mappers>

</configuration>

mapper.xml

<mapper namespace="User">
    
    <!--根据条件查询单个-->
    <select id="selectOne" resultType="com.oldlu.pojo.User" parameterType="com.oldlu.pojo.User">
        select * from user where id = #{id} and username = #{username}
    </select>

  
  <!--查询所有-->
    <select id="selectList" resultType="com.oldlu.pojo.User">
        select * from user
    </select>
</mapper>

User实体

public class User {
  //主键标识
  private Integer id;
  //用户名
  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 + '\'' + '}';
  }
}

再创建一个Maven子工程并且导入需要用到的依赖坐标

  <properties>
        <!-- Encoding -->
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <maven.compiler.encoding>UTF-8</maven.compiler.encoding>
        <java.version>11</java.version>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>

    <dependencies>
        <!-- mysql 依赖-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.6</version>
        </dependency>

        <!--junit 依赖-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <!--作用域测试范围-->
            <scope>test</scope>
        </dependency>

        <!--dom4j 依赖-->
        <dependency>
            <groupId>dom4j</groupId>
            <artifactId>dom4j</artifactId>
            <version>1.6.1</version>
        </dependency>

        <!--xpath 依赖-->
        <dependency>
            <groupId>jaxen</groupId>
            <artifactId>jaxen</artifactId>
            <version>1.1.6</version>
        </dependency>


        <!--druid连接池-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.21</version>
        </dependency>

        <!-- log日志 -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
       
    </dependencies>

Resources

public class Resources {

    /**
     * 根据配置文件的路径，加载成字节输入流，存到内存中
     * @param path
     * @return
     */
    public static InputStream getResourceAsSteam(String path){
        InputStream resourceAsStream = Resources.class.getClassLoader().getResourceAsStream(path);
        return resourceAsStream;
    }

Configuration

/**
 * 存放核心配置文件解析的内容
 */
public class Configuration {

    // 数据源对象
    private DataSource dataSource;

    // map : key :statementId  value : 封装好的MappedStatement
    private Map<String,MappedStatement> mappedStatementMap = new HashMap<>();

    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;
    }
}

MappedStatement

/**
 *  存放解析映射配置文件的内容
 *     <select id="selectOne" resultType="com.oldlu.pojo.User" parameterType="com.oldlu.pojo.User">
 *         select * from user where id = #{id} and username = #{username}
 *     </select>
 */
public class MappedStatement {

    // 1.唯一标识 （statementId namespace.id）
    private String statementId;
    // 2.返回结果类型
    private String resultType;
    // 3.参数类型
    private String parameterType;
    // 4.要执行的sql语句
    private String sql;

    // 5.mapper代理：sqlcommandType
    private String sqlcommandType;

    public String getSqlcommandType() {
        return sqlcommandType;
    }

    public void setSqlcommandType(String sqlcommandType) {
        this.sqlcommandType = sqlcommandType;
    }

    public String getStatementId() {
        return statementId;
    }

    public void setStatementId(String statementId) {
        this.statementId = statementId;
    }

    public String getResultType() {
        return resultType;
    }

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

    public String getParameterType() {
        return parameterType;
    }

    public void setParameterType(String parameterType) {
        this.parameterType = parameterType;
    }

    public String getSql() {
        return sql;
    }

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

SqlSessionFactoryBuilder

public class SqlSessionFactoryBuilder {

    /**
     * 1.解析配置文件，封装Configuration 2.创建SqlSessionFactory工厂对象
     * @return
     */
    public SqlSessionFactory build(InputStream inputStream) throws DocumentException {
        // 1.解析配置文件，封装Configuration
        XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder();
        Configuration configuration = xmlConfigBuilder.parse(inputStream);

        SqlSessionFactory defatultSqlSessionFactory = new DefatultSqlSessionFactory(configuration);
        return  defatultSqlSessionFactory;
    }

}

XMLConfigerBuilder

public class XMLConfigBuilder {
    
    private Configuration configuration;

    public XMLConfigBuilder() {
        configuration = new Configuration();
    }

    /**
     * 使用dom4j解析xml文件，封装configuration对象
     * @param inputStream
     * @return
     */
    public Configuration parse(InputStream inputStream) throws DocumentException {

        Document document = new SAXReader().read(inputStream);
        Element rootElement = document.getRootElement();

        // 解析核心配置文件中数据源部分
        List<Element> list = rootElement.selectNodes("//property");
        //  <property name="driverClassName" value="com.mysql.jdbc.Driver"></property>

        Properties properties = new Properties();
        for (Element element : list) {
            String name = element.attributeValue("name");
            String value = element.attributeValue("value");
            properties.setProperty(name,value);
        }

        // 创建数据源对象（连接池）
        DruidDataSource druidDataSource = new DruidDataSource();
        druidDataSource.setDriverClassName(properties.getProperty("driverClassName"));
        druidDataSource.setUrl(properties.getProperty("url"));
        druidDataSource.setUsername(properties.getProperty("username"));
        druidDataSource.setPassword(properties.getProperty("password"));

        // 创建好的数据源对象封装进configuration中、
        configuration.setDataSource(druidDataSource);


        // 解析映射配置文件
        // 1.获取映射配置文件的路径  2.解析  3.封装好mappedStatement
        List<Element> mapperList = rootElement.selectNodes("//mapper");
        for (Element element : mapperList) {
            String mapperPath = element.attributeValue("resource");
            InputStream resourceAsSteam = Resources.getResourceAsSteam(mapperPath);
            XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(configuration);
            xmlMapperBuilder.parse(resourceAsSteam);
        }

        return configuration;
    }
}

XMLMapperBuilder

public class XMLMapperBuilder {
 private Configuration configuration;

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

    public void parse(InputStream inputStream) throws DocumentException, ClassNotFoundException {
        Document document = new SAXReader().read(inputStream);
        Element rootElement = document.getRootElement();

        String namespace = rootElement.attributeValue("namespace");
        List<Element> select = rootElement.selectNodes("select");
        for (Element element : select) { //id的值
            String id = element.attributeValue("id");
            String paramterType = element.attributeValue("paramterType");
            String resultType = element.attributeValue("resultType"); //输入参数class
            Class<?> paramterTypeClass = getClassType(paramterType);
            //返回结果class
            Class<?> resultTypeClass = getClassType(resultType);
            //statementId
            String key = namespace + "." + id;
            //sql语句
            String textTrim = element.getTextTrim();
            //封装 mappedStatement
            MappedStatement mappedStatement = new MappedStatement();
            mappedStatement.setId(id);
            mappedStatement.setParamterType(paramterTypeClass);
            mappedStatement.setResultType(resultTypeClass);
            mappedStatement.setSql(textTrim);
            //填充 configuration
            configuration.getMappedStatementMap().put(key, mappedStatement); 

            private Class<?> getClassType (String paramterType) throws ClassNotFoundException {
                Class<?> aClass = Class.forName(paramterType);
                return aClass;
    }
}

sqlSessionFactory 接口及D efaultSqlSessionFactory 实现类

public interface SqlSessionFactory {

    /**
     * 生产sqlSession ：封装着与数据库交互的方法
     * @return
     */
    public SqlSession openSession();

}

public class DefatultSqlSessionFactory implements SqlSessionFactory {

    private Configuration configuration;

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

    @Override
    public SqlSession openSession() {

        // 执行器创建出来
        Executor executor = new SimpleExecutor();

        DefaultSqlSession defaultSqlSession = new DefaultSqlSession(configuration,executor);
        return defaultSqlSession;
    }
}

sqlSession 接口及 DefaultSqlSession 实现类

public interface SqlSession {

    /**
     * 查询所有的方法 select * from user where username like '%aaa%' and sex = ''
     * 参数1：唯一标识
     * 参数2：入参
     */
    public <E> List<E> selectList(String statementId,Object parameter) throws Exception;


    /**
     * 查询单个的方法
     */
    public <T> T selectOne(String statementId,Object parameter) throws Exception;
}

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    private Executor executor;

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

    @Override                    // user.selectList      1 tom user
    public <E> List<E> selectList(String statementId, Object params) throws Exception {

        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        // 将查询操作委派给底层的执行器
        List<E> list = executor.query(configuration,mappedStatement,params);

        return list;
    }

    @Override
    public <T> T selectOne(String statementId, Object params) throws Exception {
        List<Object> list = this.selectList(statementId, params);
        if(list.size() == 1){
            return (T) list.get(0);
        }else if(list.size() > 1){
            throw new RuntimeException("返回结果过多");
        }else {
            return null;
        }
    }
}

Executor

public interface Executor {

    <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object params) throws Exception;
}

SimpleExecutor

public class SimpleExecutor implements Executor {

    /**
     * 执行JDBC操作
     * @param configuration
     * @param mappedStatement
     * @param params
     * @param <E>
     * @return
     */
    @Override                                                                               // user product
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object params) throws Exception {

        // 1. 加载驱动，获取连接
        Connection connection = configuration.getDataSource().getConnection();

        // 2. 获取prepareStatement预编译对象
        /*
             select * from user where id = #{id} and username = #{username}
             select * from user where id = ? and username = ?
             占位符替换 ：#{}替换成？ 注意：#{id}里面的id名称要保存
         */
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSQL(sql);
        String finaLSql = boundSql.getFinaLSql();
        PreparedStatement preparedStatement = connection.prepareStatement(finaLSql);

        // 3.设置参数
         // 问题1： Object param（类型不确定 user/product/map/String）
         // 问题2：该把对象中的哪一个属性赋值给哪一个占位符呢？
        List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
        if(parameterMappings.size() > 0){
        // com.oldlu.pojo.User
        String parameterType = mappedStatement.getParameterType();
        Class<?> parameterTypeClass = Class.forName(parameterType);

        for (int i = 0; i < parameterMappings.size(); i++) {
            ParameterMapping parameterMapping = parameterMappings.get(i);
            // id
            String content = parameterMapping.getContent();
            // 反射
            Field declaredField = parameterTypeClass.getDeclaredField(content);
            // 暴力访问
            declaredField.setAccessible(true);
            Object value = declaredField.get(params);
            preparedStatement.setObject(i+1 ,value);
        }
        }

        // 4.执行sql,发起查询
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = Class.forName(resultType);

        ArrayList<E> list = new ArrayList<>();
        // 5.遍历封装
        while (resultSet.next()){
            // 元数据信息中包含了字段名 字段的值
            ResultSetMetaData metaData = resultSet.getMetaData();
            Object obj = resultTypeClass.newInstance();
            for (int i = 1; i <= metaData.getColumnCount() ; i++) {

                // id  username
                String columnName = metaData.getColumnName(i);
                Object value = resultSet.getObject(columnName);
                // 属性描述器
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName,resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();
                writeMethod.invoke(obj,value);
            }
            list.add((E) obj);
        }
        return list;
    }

    /**
     *  1.将sql中#{}替换成？ 2.将#{}里面的值保存
     * @param sql
     * @return
     */
    private BoundSql getBoundSQL(String sql) {
        // 标记处理器：配合标记解析器完成标记的解析工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();

        // 标记解析器
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
        String finalSql = genericTokenParser.parse(sql);

        // #{}里面的值的集合
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();

        BoundSql boundSql = new BoundSql(finalSql, parameterMappings);

        return boundSql;
    }
}

BoundSql

public class BoundSql {
   //解析过后的sql语句
    private String sqlText;
    //解析出来的参数
    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;
    }
}

5 自定义持久层框架优化

通过上述我们的自定义框架，我们解决了JDBC操作数据库带来的一些问题：例如频繁创建释放数据库连接，硬编码，手动封装返回结果集等问题，但是现在我们继续来分析刚刚完成的自定义框架代码，有没有什么问题？

问题如下：

dao的实现类中存在重复的代码，整个操作的过程模板重复(创建sqlsession,调用sqlsession方法，关闭 sqlsession)

dao的实现类中存在硬编码，调用sqlsession的方法时，参数statement的id硬编码

解决：使用代理模式来创建接口的代理对象

  @Test
    public void test2() throws Exception {
        InputStream resourceAsSteam = Resources.getResourceAsSteam(path： "sqlMapConfig.xml")
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsSteam);
        SqlSession sqlSession = build.openSession();
        User user = new User();
        user.setld(l);
        user.setUsername("tom");
        //代理对象
        UserMapper userMapper = sqlSession.getMappper(UserMapper.class);
        User userl = userMapper.selectOne(user);
        System・out.println(userl);
    }

在sqlSession中添加方法

public interface SqlSession {
   public <T> T getMappper(Class<?> mapperClass);

实现类

package com.oldlu.sqlSession;

import com.oldlu.executor.Executor;
import com.oldlu.pojo.Configuration;
import com.oldlu.pojo.MappedStatement;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Collection;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;
    private Executor executor;

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

    @Override
    public <E> List<E> selectList(String statementId, Object param) throws Exception {

        // 要传递什么参数呢？
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<E> list = executor.query(configuration,mappedStatement,param);
        return list;
    }

    @Override
    public <T> T selectOne(String statementId, Object param) throws Exception {
        // 调用selectList方法
        List<Object> list = selectList(statementId, param);
        if(list.size() == 1){
            return (T) list.get(0);
        }else if(list.size() > 1){
            throw new RuntimeException("返回结果过多...");
        }
        return null;
    }

    /**
     * 生成代理对象
     * @param mapperClass
     * @param <T>
     * @return
     */
    @Override
    public <T> T getMapper(Class<?> mapperClass) {

        // 使用JDK动态代理生成代理对象
        Object proxyInstance = Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {

            // 参数1：Object o:代理对象的引用，很少用
            // 参数2：Method method ：当前被调用的方法对象
            // 参数3：Object[] objects：被调用的方法的参数
            @Override
            public Object invoke(Object o, Method method, Object[] objects) throws Throwable {

                // 具体的逻辑：执行底层的JDBC
                // 思路：通过调用sqlSession的方法来完成执行
                // 问题1：如何获取statementId 根据method获取
                Class<?> declaringClass = method.getDeclaringClass();
                // 类全路径= namespace的值
                String className = declaringClass.getName();
                String methodName = method.getName();
                String statementId = className + "." + methodName;
                MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);

                // 问题2：该调用增删改查什么方法呢？ 优化：sqlCommandType
                String sqlCommandType = mappedStatement.getSqlCommandType();
                switch (sqlCommandType){
                    case "select":
                        //查询操作
                        //问题3：调selectOne还是调selectAll呢？
                        Class<?> returnType = method.getReturnType();
                        boolean assignableFrom = Collection.class.isAssignableFrom(returnType);
                        if(assignableFrom){
                            if(mappedStatement.getParameterType() !=null) {
                              return   selectList(statementId, objects[0]);
                            }
                            return selectList(statementId, null);
                        }
                        return selectOne(statementId,objects[0]);

                    case "update":
                        // 更新操作
                        break;
                    case "insert":
                        // 更新操作
                        break;
                    case "delete":
                        // 更新操作
                        break;
                }


                return null;
            }
        });


        return (T) proxyInstance;
    }
}