手寫Mybatis框架

分析

配置文件

log4j.properties

# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, CONSOLE            debug   info   warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE

# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE

# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n

# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=d:\axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n

SqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <!--配置環境-->
    <environments default="mysql">
        <!--配置mysql環境-->
        <environment id="mysql">
            <!--配置事務類型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--配置數據源(連接池)-->
            <dataSource type="POOLED">
                <!--配置連接數據庫的4個基本信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"></property>
                <property name="url" value="jdbc:mysql://localhost:3306/eesy"></property>
                <property name="username" value="root"></property>
                <property name="password" value="123456"></property>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!--<mapper resource="com/sx/dao/IUserDao.xml"></mapper>-->
        <mapper class="com.sx.dao.IUserDao"></mapper>
    </mappers>
</configuration>

IUserDao.xml

<?xml version="1.0" encoding="UTF-8"?>
<mapper namespace="com.sx.dao.IUserDao">
    <!--配置查詢所有User的方法和返回類型-->
    <select id="findAll" resultType="com.sx.domain.User">
        select * from user
    </select>
</mapper>

domain和IUserDao

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    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;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

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

public interface IUserDao {
    /**
     * 查找所有用戶
     *
     * @return
     */
    @Select("select * from user")
    List<User> findAll();

}

1.讀取配置文件

public class Resources {
    /**
     * 根據傳入的參數,獲取一個字節輸入流
     *
     * @param filePath
     * @return
     */
    public static InputStream getResourceAsStream(String filePath) {
        return Resources.class.getClassLoader().getResourceAsStream(filePath);
    }
}

2.構建SqlSessionFactoryBuilder用於創建SqlSessionFactory對象

public class SqlSessionFactoryBuilder {
    /**
     * 根據參數的字節輸入流構建一個SqlSessionFactory工廠
     * @param is
     * @return
     */
    public SqlSessionFactory build(InputStream is) {
        Configuration cfg = XMLConfigBuilder.loadConfiguration(is);
        return new DefaultSqlSessionFactory(cfg);
    }
}

3.創建SqlSessionFactory、SqlSession接口

public interface SqlSessionFactory {
    /**
     * 用於打開一個新的Session對象
     * @return
     */
    SqlSession openSession();
}

public interface SqlSession {
    /**
     * 根據參數創建代理對象
     * @param daoInterfaceClass dao接口字節碼
     * @param <T>
     * @return
     */
    <T> T getMapper(Class<T> daoInterfaceClass);

    /**
     * 釋放資源
     */
    void close();
}

4.創建Configuration（Mybatis中的配置類）

public class Configuration {
    private String driver;
    private String url;
    private String username;
    private String password;

    private Map<String, Mapper> mappers = new HashMap<>();

    public Map<String, Mapper> getMappers() {
        return mappers;
    }

    public void setMappers(Map<String, Mapper> mappers) {
        this.mappers.putAll(mappers);
    }

    public String getDriver() {
        return driver;
    }

    public void setDriver(String driver) {
        this.driver = driver;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getUsername() {
        return username;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

5.創建Mapper（用於封裝執行的SQL語句和結果類型的全限定類名）

public class Mapper {
    private String queryString;
    private String resultType;

    public String getQueryString() {
        return queryString;
    }

    public void setQueryString(String queryString) {
        this.queryString = queryString;
    }

    public String getResultType() {
        return resultType;
    }

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

6.創建SqlSessionFactory的實現類

public class DefaultSqlSessionFactory implements SqlSessionFactory {
    private Configuration cfg;

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

    /**
     * 用於創建一個新的操作數據庫的對象
     *
     * @return
     */
    @Override
    public SqlSession openSession() {
        return new DefaultSqlSession(cfg);
    }
}

7.創建SqlSession的實現類

public class DefaultSqlSession implements SqlSession {
    private Configuration cfg;
    private Connection con;

    public DefaultSqlSession(Configuration cfg) {
        this.cfg = cfg;
        con = DataSourceUtil.getConnection(cfg);
    }

    /**
     * 用於創建代理對象
     *
     * @param daoInterfaceClass dao接口字節碼
     * @param <T>
     * @return
     */
    @Override
    public <T> T getMapper(Class<T> daoInterfaceClass) {
        return (T) Proxy.newProxyInstance(daoInterfaceClass.getClassLoader(),
                new Class[]{daoInterfaceClass}, new MapperProxy(cfg.getMappers(), con));
    }

    /**
     * 用於釋放資源
     */
    @Override
    public void close() {
        if (con != null) {
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

8.創建數據源的工具類

public class DataSourceUtil {
    /**
     * 用於獲取一個鏈接
     *
     * @param cfg
     * @return
     */
    public static Connection getConnection(Configuration cfg) {
        try {
            Class.forName(cfg.getDriver());
            return DriverManager.getConnection(cfg.getUrl(), 
            cfg.getUsername(), cfg.getPassword());
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

9.用於解析配置文件的工具類

public class XMLConfigBuilder {


    /**
     * 解析主配置文件，把裏面的內容填充到DefaultSqlSession所需要的地方
     * 使用的技術：
     * dom4j+xpath
     */
    public static Configuration loadConfiguration(InputStream config) {
        try {
            //定義封裝連接信息的配置對象（mybatis的配置對象）
            Configuration cfg = new Configuration();

            //1.獲取SAXReader對象
            SAXReader reader = new SAXReader();
            //2.根據字節輸入流獲取Document對象
            Document document = reader.read(config);
            //3.獲取根節點
            Element root = document.getRootElement();
            //4.使用xpath中選擇指定節點的方式，獲取所有property節點
            List<Element> propertyElements = root.selectNodes("//property");
            //5.遍歷節點
            for (Element propertyElement : propertyElements) {
                //判斷節點是連接數據庫的哪部分信息
                //取出name屬性的值
                String name = propertyElement.attributeValue("name");
                if ("driver".equals(name)) {
                    //表示驅動
                    //獲取property標籤value屬性的值
                    String driver = propertyElement.attributeValue("value");
                    cfg.setDriver(driver);
                }
                if ("url".equals(name)) {
                    //表示連接字符串
                    //獲取property標籤value屬性的值
                    String url = propertyElement.attributeValue("value");
                    cfg.setUrl(url);
                }
                if ("username".equals(name)) {
                    //表示用戶名
                    //獲取property標籤value屬性的值
                    String username = propertyElement.attributeValue("value");
                    cfg.setUsername(username);
                }
                if ("password".equals(name)) {
                    //表示密碼
                    //獲取property標籤value屬性的值
                    String password = propertyElement.attributeValue("value");
                    cfg.setPassword(password);
                }
            }
            //取出mappers中的所有mapper標籤，判斷他們使用了resource還是class屬性
            List<Element> mapperElements = root.selectNodes("//mappers/mapper");
            //遍歷集合
            for (Element mapperElement : mapperElements) {
                //判斷mapperElement使用的是哪個屬性
                Attribute attribute = mapperElement.attribute("resource");
                if (attribute != null) {
                    System.out.println("使用的是XML");
                    //表示有resource屬性，用的是XML
                    //取出屬性的值
                    String mapperPath = attribute.getValue();//獲取屬性的值"com/itheima/dao/IUserDao.xml"
                    //把映射配置文件的內容獲取出來，封裝成一個map
                    Map<String, Mapper> mappers = loadMapperConfiguration(mapperPath);
                    //給configuration中的mappers賦值
                    cfg.setMappers(mappers);
                } else {
                    System.out.println("使用的是註解");
                    //表示沒有resource屬性，用的是註解
                    //獲取class屬性的值
                    String daoClassPath = mapperElement.attributeValue("class");
                    //根據daoClassPath獲取封裝的必要信息
                    Map<String, Mapper> mappers = loadMapperAnnotation(daoClassPath);
                    //給configuration中的mappers賦值
                    cfg.setMappers(mappers);
                }
            }
            //返回Configuration
            return cfg;
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            try {
                config.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }

    /**
     * 根據傳入的參數，解析XML，並且封裝到Map中
     *
     * @param mapperPath 映射配置文件的位置
     * @return map中包含了獲取的唯一標識（key是由dao的全限定類名和方法名組成）
     * 以及執行所需的必要信息（value是一個Mapper對象，裏面存放的是執行的SQL語句和要封裝的實體類全限定類名）
     */
    private static Map<String, Mapper> loadMapperConfiguration(String mapperPath) throws IOException {
        InputStream in = null;
        try {
            //定義返回值對象
            Map<String, Mapper> mappers = new HashMap<String, Mapper>();
            //1.根據路徑獲取字節輸入流
            in = Resources.getResourceAsStream(mapperPath);
            //2.根據字節輸入流獲取Document對象
            SAXReader reader = new SAXReader();
            Document document = reader.read(in);
            //3.獲取根節點
            Element root = document.getRootElement();
            //4.獲取根節點的namespace屬性取值
            String namespace = root.attributeValue("namespace");//是組成map中key的部分
            //5.獲取所有的select節點
            List<Element> selectElements = root.selectNodes("//select");
            //6.遍歷select節點集合
            for (Element selectElement : selectElements) {
                //取出id屬性的值      組成map中key的部分
                String id = selectElement.attributeValue("id");
                //取出resultType屬性的值  組成map中value的部分
                String resultType = selectElement.attributeValue("resultType");
                //取出文本內容            組成map中value的部分
                String queryString = selectElement.getText();
                //創建Key
                String key = namespace + "." + id;
                //創建Value
                Mapper mapper = new Mapper();
                mapper.setQueryString(queryString);
                mapper.setResultType(resultType);
                //把key和value存入mappers中
                mappers.put(key, mapper);
            }
            return mappers;
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            in.close();
        }
    }

    /**
     * 根據傳入的參數，得到dao中所有被select註解標註的方法。
     * 根據方法名稱和類名，以及方法上註解value屬性的值，組成Mapper的必要信息
     *
     * @param daoClassPath
     * @return
     */
    private static Map<String, Mapper> loadMapperAnnotation(String daoClassPath) throws Exception {
        //定義返回值對象
        Map<String, Mapper> mappers = new HashMap<String, Mapper>();

        //1.得到dao接口的字節碼對象
        Class daoClass = Class.forName(daoClassPath);
        //2.得到dao接口中的方法數組
        Method[] methods = daoClass.getMethods();
        //3.遍歷Method數組
        for (Method method : methods) {
            //取出每一個方法，判斷是否有select註解
            boolean isAnnotated = method.isAnnotationPresent(Select.class);
            if (isAnnotated) {
                //創建Mapper對象
                Mapper mapper = new Mapper();
                //取出註解的value屬性值
                Select selectAnno = method.getAnnotation(Select.class);
                String queryString = selectAnno.value();
                mapper.setQueryString(queryString);
                //獲取當前方法的返回值，還要求必須帶有泛型信息
                Type type = method.getGenericReturnType();//List<User>
                //判斷type是不是參數化的類型
                if (type instanceof ParameterizedType) {
                    //強轉
                    ParameterizedType ptype = (ParameterizedType) type;
                    //得到參數化類型中的實際類型參數
                    Type[] types = ptype.getActualTypeArguments();
                    //取出第一個
                    Class domainClass = (Class) types[0];
                    //獲取domainClass的類名
                    String resultType = domainClass.getName();
                    //給Mapper賦值
                    mapper.setResultType(resultType);
                }
                //組裝key的信息
                //獲取方法的名稱
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();
                String key = className + "." + methodName;
                //給map賦值
                mappers.put(key, mapper);
            }
        }
        return mappers;
    }
}

10.用於執行SQL語句並封裝結果集

public class Executor {

    public <E> List<E> selectList(Mapper mapper, Connection conn) {
        PreparedStatement pstm = null;
        ResultSet rs = null;
        try {
            //1.取出mapper中的數據
            String queryString = mapper.getQueryString();//select * from user
            String resultType = mapper.getResultType();//com.itheima.domain.User
            Class domainClass = Class.forName(resultType);
            //2.獲取PreparedStatement對象
            pstm = conn.prepareStatement(queryString);
            //3.執行SQL語句，獲取結果集
            rs = pstm.executeQuery();
            //4.封裝結果集
            List<E> list = new ArrayList<E>();//定義返回值
            while (rs.next()) {
                //實例化要封裝的實體類對象
                E obj = (E) domainClass.newInstance();

                //取出結果集的元信息：ResultSetMetaData
                ResultSetMetaData rsmd = rs.getMetaData();
                //取出總列數
                int columnCount = rsmd.getColumnCount();
                //遍歷總列數
                for (int i = 1; i <= columnCount; i++) {
                    //獲取每列的名稱，列名的序號是從1開始的
                    String columnName = rsmd.getColumnName(i);
                    //根據得到列名，獲取每列的值
                    Object columnValue = rs.getObject(columnName);
                    //給obj賦值：使用Java內省機制（藉助PropertyDescriptor實現屬性的封裝）
                    PropertyDescriptor pd = new PropertyDescriptor(columnName, domainClass);//要求：實體類的屬性和數據庫表的列名保持一種
                    //獲取它的寫入方法
                    Method writeMethod = pd.getWriteMethod();
                    //把獲取的列的值，給對象賦值
                    writeMethod.invoke(obj, columnValue);
                }
                //把賦好值的對象加入到集合中
                list.add(obj);
            }
            return list;
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            release(pstm, rs);
        }
    }


    private void release(PreparedStatement pstm, ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        if (pstm != null) {
            try {
                pstm.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

11.select註解

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Select {
    /**
     * 接收sql語句
     * @return
     */
    String value();
}

12.測試類

public class MybatisTest {
    public static void main(String[] args) throws Exception {
        //1.讀取配置文件
        InputStream is = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.創建SqlSessionFactory工廠
        SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder();
        SqlSessionFactory ssf = ssfb.build(is);
        //3.使用工廠生產SqlSession對象
        SqlSession ss = ssf.openSession();
        //4.使用SqlSession創建Dao接口的代理對象
        IUserDao iud = ss.getMapper(IUserDao.class);
        //5.使用代理對象執行方法
        List<User> users = iud.findAll();
        for (User user : users) {
            System.out.println(user);
        }
        //6.釋放資源
        ss.close();
        is.close();
    }
}