【4】自定义持久化框架

1.1 分析 JDBC 操作问题

public static void main(String[] args) { Connection connection = null;
        PreparedStatement preparedStatement = null; ResultSet resultSet = null;
        try {
// 加载数据库驱动
            Class.forName("com.mysql.jdbc.Driver");
// 通过驱动管理类获取数据库链接
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis? characterEncoding=utf-8", "root", "root");
// 定义sql语句？表示占位符
            String sql = "select * from user where username = ?";
// 获取预处理statement
            preparedStatement = connection.prepareStatement(sql);
// 设置参数，第⼀个参数为sql语句中参数的序号(从1开始)，第⼆个参数为设置的参数值
            preparedStatement.setString(1, "tom");
// 向数据库发出sql执⾏查询，查询出结果集
            resultSet = preparedStatement.executeQuery();
// 遍历查询结果集
            while (resultSet.next()) {
                int id = resultSet.getInt("id");
                String username = resultSet.getString("username");
// 封 装 User user.setId(id);
                user.setUsername(username);
            }
            System.out.println(user);
        }
    } catch (Exception e) { e.printStackTrace();
    } finally

    {
// 释放资源
        if (resultSet != null) {
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (preparedStatement != null) {
            try {
                preparedStatement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (connection != null) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

JDBC 问题总结：

原始jdbc开发存在的问题如下：

1、数据库连接创建、释放频繁造成系统资源浪费，从⽽影响系统性能。

2、Sql语句在代码中硬编码，造成代码不易维护，实际应⽤中sql变化的可能较⼤，sql变动需要改变 java代码。

3、使⽤preparedStatement向占有位符号传参数存在硬编码，因为sql语句的where条件不⼀定，可能多也可能少，修改sql还要修改代码，系统不易维护。

4、对结果集解析存在硬编码(查询列名)，sql变化导致解析代码变化，系统不易维护，如果能将数据  库记录封装成pojo对象解析⽐较⽅便

1.2 问题解决思路

①使⽤数据库连接池初始化连接资源

②将sql语句抽取到xml配置⽂件中

③使⽤反射、内省等底层技术，⾃动将实体与表进⾏属性与字段的⾃动映射

1.3 ⾃定义框架设计

使⽤端：

提供核⼼配置⽂件：

sqlMapConfig.xml : 存放数据源信息，引mapper.

xmlMapper.xml : sql语句的配置⽂件信息

框架端：

1. 读取配置⽂件

读取完成以后以流的形式存在，我们不能将读取到的配置信息以流的形式存放在内存中，不好操作，可以创建javaBean来存储

（1） Configuration : 存放数据库基本信息、Map<唯⼀标识，Mapper> 唯⼀标识：namespace + "."+ id

（2） MappedStatement：sql语句、statement类型、输⼊参数java类型、输出参数java类型

 2. 解析配置⽂件

创建sqlSessionFactoryBuilder类：

⽅法：sqlSessionFactory build()：

• 第⼀：使⽤dom4j解析配置⽂件，将解析出来的内容封装到Configuration和MappedStatement中    
• 第⼆：创建SqlSessionFactory的实现类DefaultSqlSession

3. 创建SqlSessionFactory：

⽅法：openSession() : 获取sqlSession接⼝的实现类实例对象

4. 创建sqlSession接⼝及实现类：主要封装crud⽅法

⽅法：selectList(String statementId,Object param)：查询所有selectOne(String statementId,Object param)：查询单个 具体实现：封装JDBC完成对数据库表的查询操作

涉及到的设计模式：

Builder构建者设计模式、⼯⼚模式、代理模式

1.4 ⾃定义框架实现

在使⽤端项⽬中创建配置配置⽂件创建 sqlMapConfig.xml

〈configuration〉
<!--数据库连接信息-->
<property  name="driverClass" value="com.mysql.jdbc.Driver"></property>
<property  name="jdbcUrl" value="jdbc:mysql:///zdy_mybatis"></property>
<property name="user" value="root"></property>
<property name="password" value="root"></property>
<! --引⼊sql配置信息-->
<mapper resource="mapper.xml"></mapper>
</configuration>

mapper.xml

<mapper namespace="User">
<select id="selectOne" paramterType="com.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

@Data
public class User {
    //主键标识
    private Integer id;
    //⽤户名
    private String username;

}

再创建⼀个Maven⼦⼯程并且导⼊需要⽤到的依赖坐标

<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.encoding>UTF-8</maven.compiler.encoding>
<java.version>1.8</java.version>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.17</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>

Configuration

public class Configuration {
    //数据源
    private DataSource dataSource;
    //map集合： key:statementId value:MappedStatement
    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;
    }
}

MappedStatemen

public class MappedStatement {
    //id
    private Integer id;
    //sql语句
    private String sql;
    //输⼊参数
    private Class<?> paramterType;
    //输出参数
    private Class<?> resultType;
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getSql() {
        return sql;
    }
    public void setSql(String sql) {
        this.sql = sql;
    }
    public Class<?> getParamterType() {
        return paramterType;
    }
    public void setParamterType(Class<?> paramterType) {
        this.paramterType = paramterType;
    }
    public Class<?> getResultType() {
        return resultType;
    }
    public void setResultType(Class<?> resultType) {
        this.resultType = resultType;
    }
}

Resources

public class Resources {
    public static InputStream getResourceAsSteam(String path){ InputStream
            resourceAsStream =
            Resources.class.getClassLoader.getResourceAsStream(path);
        return resourceAsStream;
    }
}

SqlSessionFactoryBuilder

public class SqlSessionFactoryBuilder {
    private Configuration configuration;

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

    public SqlSessionFactory build(InputStream inputStream) throws
            DocumentException, PropertyVetoException, ClassNotFoundException {
        //1.解析配置⽂件，封装Configuration XMLConfigerBuilder
        xmlConfigerBuilder = new
                XMLConfigerBuilder(configuration);
        Configuration configuration =
                xmlConfigerBuilder.parseConfiguration(inputStream);
        //2.创建 sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new
                DefaultSqlSessionFactory(configuration);
        return sqlSessionFactory;
    }
}

XMLConfigerBuilder

public class XMLConfigerBuilder {
    private Configuration configuration;

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

    public Configuration parseConfiguration(InputStream inputStream) throws
            DocumentException, PropertyVetoException, ClassNotFoundException {
        Document document = new SAXReader().read(inputStream);
//<configuation>
        Element rootElement = document.getRootElement();
        List<Element> propertyElements =
                rootElement.selectNodes("//property");
        Properties properties = new Properties();
        for (Element propertyElement : propertyElements) {
            String name = propertyElement.attributeValue("name");
            String value = propertyElement.attributeValue("value");
            properties.setProperty(name, value);
        }
        //连接池
        ComboPooledDataSource comboPooledDataSource = new
                ComboPooledDataSource();

        comboPooledDataSource.setDriverClass(properties.getProperty("driverClass"));
        comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl"));
        comboPooledDataSource.setUser(properties.getProperty("username"));
        comboPooledDataSource.setPassword(properties.getProperty("password"));
        //填充 configuration
        configuration.setDataSource(comboPooledDataSource);
        //mapper 部分
        List<Element> mapperElements = rootElement.selectNodes("//mapper");
        XMLMapperBuilder xmlMapperBuilder = new
                XMLMapperBuilder(configuration);
        for (Element mapperElement : mapperElements) {
            String mapperPath = mapperElement.attributeValue("resource");
            InputStream resourceAsSteam =
                    Resources.getResourceAsSteam(mapperPath);
            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DefaultSqlSessionFactory 实现类

public interface SqlSessionFactory {
    public SqlSession openSession();
}
public class DefaultSqlSessionFactory implements SqlSessionFactory {
    private Configuration configuration;
    public DefaultSqlSessionFactory(Configuration configuration) {
        this.configuration = configuration;
    }
    public SqlSession openSession(){
        return new DefaultSqlSession(configuration);
    }
}

sqlSession 接⼝及 DefaultSqlSession 实现类

public interface SqlSession {
    public <E> List<E> selectList(String statementId, Object... param)
    Exception;
    public <T> T selectOne(String statementId,Object... params) throws
            Exception;
    public void close() throws SQLException;
}

public class DefaultSqlSession implements SqlSession {
    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
        //处理器对象
        private Executor simpleExcutor = new SimpleExecutor();
        public <E > List < E > selectList(String statementId, Object...param)
throws Exception {
            MappedStatement mappedStatement =
                    configuration.getMappedStatementMap().get(statementId);
            List<E> query = simpleExcutor.query(configuration,
                    mappedStatement, param);
            return query;
        }
        //selectOne 中调⽤ selectList
        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("返回结果过多");
            }
        }
        public void close () throws SQLException {
            simpleExcutor.close();
        }
    }
}

Executor

public interface Executor {
    <E> List<E> query(Configuration configuration, MappedStatement
            mappedStatement,Object[] param) throws Exception;
    void close() throws SQLException;
}

SimpleExecutor

public class SimpleExecutor implements Executor {
    private Connection connection = null;
    public <E> List<E> query(Configuration configuration, MappedStatement
            mappedStatement, Object[] param) throws SQLException, NoSuchFieldException,
            IllegalAccessException, InstantiationException, IntrospectionException,
            InvocationTargetException {
        //获取连接
        connection = configuration.getDataSource().getConnection();
        // select * from user where id = #{id} and username = #{username}
        String sql = mappedStatement.getSql();
        //对sql进⾏处理
        BoundSql boundsql = getBoundSql(sql);
        // select * from where id = ? and username = ?
        String finalSql = boundsql.getSqlText();
        //获取传⼊参数类型
        Class<?> paramterType = mappedStatement.getParamterType();
        //获取预编译preparedStatement对象
        PreparedStatement preparedStatement =
                connection.prepareStatement(finalSql);
        List<ParameterMapping> parameterMappingList =
                boundsql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String name = parameterMapping.getName();
            //反射
            Field declaredField = paramterType.getDeclaredField(name);
            declaredField.setAccessible(true);
            //参数的值
            Object o = declaredField.get(param[0]);
//给占位符赋值
            preparedStatement.setObject(i + 1, o);
        }
        ResultSet resultSet = preparedStatement.executeQuery();
        Class<?> resultType = mappedStatement.getResultType();
        ArrayList<E> results = new ArrayList<E>();
        while (resultSet.next()) {
            ResultSetMetaData metaData = resultSet.getMetaData();
            (E) resultType.newInstance();
            int columnCount = metaData.getColumnCount();
            for (int i = 1; i <= columnCount; i++) {
                //属性名
                String columnName = metaData.getColumnName(i);
                //属性值
                Object value = resultSet.getObject(columnName);
                //创建属性描述器，为属性⽣成读写⽅法
                PropertyDescriptor propertyDescriptor = new
                        PropertyDescriptor(columnName, resultType);
                //获取写⽅法
                Method writeMethod = propertyDescriptor.getWriteMethod();
                //向类中写⼊值
                writeMethod.invoke(o, value);
            }
            results.add(o);
        }
        return results;
    }
    @Override
    public void close() throws SQLException {
        connection.close();
    }
    private BoundSql getBoundSql(String sql) {
        //标记处理类：主要是配合通⽤标记解析器GenericTokenParser类完成对配置⽂件等的解
        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，完成了代码⽚段中的占位符的解析，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);
        String parse = genericTokenParser.parse(sql);
        List<ParameterMapping> parameterMappings =
                parameterMappingTokenHandler.getParameterMappings();
        BoundSql boundSql = new BoundSql(parse, 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;
    }
}

1.5 ⾃定义框架优化

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

@Override
public <T> T getMappper(Class<?> mapperClass) {
        T o = (T) Proxy.newProxyInstance(mapperClass.getClassLoader(), new Class[] {mapperClass}, new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// selectOne
        String methodName = method.getName();
// className:namespace
        String className = method.getDeclaringClass().getName();
//statementid
        String key = className+"."+methodName; MappedStatement mappedStatement =
        configuration.getMappedStatementMap().get(key);
        Type genericReturnType = method.getGenericReturnType(); ArrayList arrayList = new ArrayList<> ();
//判断是否实现泛型类型参数化
        if(genericReturnType instanceof ParameterizedType){ return selectList(key,args);
        return selectOne(key,args);
        }
        });
        return o;
}