自定義mybatis，手寫源碼

通過將mybatis依賴刪除來手動實現功能

(同時涵蓋了註解和xml配置的自定義mybatis）

pom.xml依賴

<dependencies>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!-- log4j日誌，可添加可不添加-->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <!--        Junit測試-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
            <scope>test</scope>
        </dependency>
        <!--        dom4j-->
        <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>

其中，分別爲

public class Resources
public class SqlSessionFactoryBuilder
public interface SqlSessionFactory
public interface SqlSession

目錄結構

1、創建Resources類

public class Resources {
    public static InputStream getResourceAsStream(String filePath) {
        return Resources.class.getClassLoader().getResourceAsStream(filePath);
    }
}

2、創建SqlSessionFactoryBuilder類

public class SqlSessionFactoryBuilder {

    private Configuration cfg;

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

    public SqlSessionFactoryBuilder() {
    }

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

3、創建SqlSessionFactory接口

public interface SqlSessionFactory {
    SqlSession openSession();
}

4、創建SqlSession接口

public interface SqlSession {
    <T> T getMapper(Class<T> doInterfaceClass);

    void close();
}

5、創建工具類XMLConfigBuilder

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/lp/dao/UserDao.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
                    System.out.println(mappers.entrySet());
                    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;
    }

}

6、工具類中需要Configuration，創建Configuration類

public class Configuration {
    private String driver;
    private String url;
    private String username;
    private String password;
    private Map<String,Mapper> mappers=new HashMap<String, Mapper>();

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

    public void setMappers(Map<String, Mapper> mappers) {
        System.out.println(mappers.entrySet());
        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;
    }
}

7、工具類中需要Mapper，創建Mapper類

public class Mapper {
    //sql
    private String queryString;
    //實體類的全限定類名
    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;
    }


}

8、DefaultSqlSession是SqlSession的實現類

/**
 * SqlSession接口的實現類
 */
public class DefaultSqlSession implements SqlSession {

    private Configuration cfg;
    private Connection connection;

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

    public <T> T getMapper(Class<T> doInterfaceClass) {
        return(T) Proxy.newProxyInstance(doInterfaceClass.getClassLoader(),
                new Class[]{doInterfaceClass},new MapperProxy(cfg.getMappers(),connection));


    }

    public void close() {
        if (connection != null) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

9、DefaultSqlSessionFactory是SqlSessionFactory的實現類

/**
 * SqlSessionFactory接口的實現類
 */
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對象
     * @return
     */
    public SqlSession openSession() {
        return new DefaultSqlSession(cfg);
    }
}

10、在DefaultSqlSession中需要通過反射獲取全限定類名，需要用到MapperProxy類

public class MapperProxy implements InvocationHandler {

    //map的key是全限定類名+方法名
    private Map<String,Mapper> mappers;
    private Connection conn;

    public MapperProxy(Map<String,Mapper> mappers,Connection conn){
        this.mappers = mappers;
        this.conn = conn;
    }
    /**
     * 用於對方法進行增強，其實就是調用selectList方法
     *
     * @param proxy
     * @param method
     * @param args
     * @return
     * @throws Throwable
     */
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        //獲取方法名
        String methodName = method.getName();
        //獲取方法所在類名稱
        String className = method.getDeclaringClass().getName();
        //組合key
        String key = className + "." + methodName;
        System.out.println(key);
        //獲取mapper中的Mapper對象
        Mapper mapper = mappers.get(key);

        //判斷是否有mapper
        if (mapper == null) {
            throw new IllegalArgumentException("傳入參數有誤！");
        }
        //調用工具類查詢所有
        return new Executor().selectList(mapper, conn);
    }
}

11、我們需要DataSourceUtil工具類來獲取數據源

/**
 * 創建數據源的工具類
 */
public class DataSourceUtil {
    public static Connection getConnection(Configuration cfg) {
        try {
            Class.forName(cfg.getDriver());
            return DriverManager.getConnection(cfg.getUrl(), cfg.getUsername(), cfg.getPassword());
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }
}

12、Executor類來負責執行SQL語句，並且封裝結果集

/**
 * @author lp
 * 負責執行SQL語句，並且封裝結果集
 */
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.lp.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();
            }
        }
    }
}

13、利用註解操作時，我們需要Select

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Select {
    String value();
}

14、測試類

public class test {
    public static void main(String[] args) throws IOException {
        //讀取配置文件
        InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");

        //創建SqlSessionFactory工廠
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sessionFactory = builder.build(inputStream);

        //使用工廠生成SqlSession對象
        SqlSession session = sessionFactory.openSession();

        //使用SqlSession創建Dao接口的代理對象
        UserDao userDao = session.getMapper(UserDao.class);

        //使用代理對象執行方法
        for (User user : userDao.getAll()) {
            System.out.println(user);
        }

        // 釋放資源
        session.close();
        inputStream.close();
    }
}

15、mybatis配置文件SqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <!--    配置環境-->
    <environments default="mysql">
        <!--        配置mysql的環境-->
        <environment id="mysql">
            <!--            配置事務的類型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--            配置數據源（連接池）-->
            <dataSource type="POOLED">
                <!--            配置連接數據庫的四個基本信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///eesy"/>
                <property name="username" value="root"/>
                <property name="password" value="密碼"/>
            </dataSource>
        </environment>
    </environments>
    <!--    指定映射配置文件，映射配置文件指的是每個dao獨立的配置文件-->
    <mappers>
<!--        <mapper resource="com/lp/dao/UserDao.xml"/>-->
        <mapper class="com.lp.dao.UserDao"/>

    </mappers>
</configuration>

16、log4j.properties配置文件

# 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

17、映射文件UserDao.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--namespace名稱必須是dao的全限定類名-->
<mapper namespace="com.lp.dao.UserDao">
    <!--    配置查詢所有,id必須要與接口一致-->
    <select id="getAll" resultType="com.lp.domain.User">
        select * from user;
    </select>
</mapper>

18、UserDao接口

public interface UserDao {
    /**
     * 查詢所有
     * @return
     */
    @Select("select * from user")
    List<User> getAll();
}

19、User實體類

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

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

    public User(Integer id, String username, Date birthday, String sex, String address) {
        this.id = id;
        this.username = username;
        this.birthday = birthday;
        this.sex = sex;
        this.address = address;
    }

    public User() {
    }
}

代碼花了我很多時間，因爲過程中遇到大大小小的問題，最後通過debug來找出了原因，希望大家出問題可以自行debug或者百度，這樣印象更深刻，個人學習筆記，覺得沒有用的勿噴！大家學習階段希望能夠多動手實踐，這樣纔會帶來更好的學習效果！