解析MyBatis源码实现自定义持久层框架

<configuration>
        <!--数据库配置信息-->
    <dataSource>
        <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
        <property name="jdbcUrl" value="jdbc:mysql:///learning_db"></property>
        <property name="username" value="root"></property>
        <property name="password" value="123456"></property>
    </dataSource>
    <!--存放mapper.xml的全路径-->
    <mapper resource="UserMapper.xml"></mapper>
</configuration>

<mapper namespace="com.snf.mapper.UserMapper">
    <!--sql的唯一标识：namespace.id来组成 ： mappedStatementId-->
    <select id="findAll" resultType="com.snf.domain.User" >
        select * from user
    </select>
    <!--
        User user = new User()
        user.setId(1);
        user.setUsername("zhangsan")
    -->
    <select id="findByCondition" resultType="com.snf.domain.User" parameterType="com.snf.domain.User">
        select * from user where id = #{id} and username = #{username}
    </select>
</mapper>

public class User {
    private Integer id;
    private String username;
    public User() {
    }
    public User(Integer id, String username) {
        this.id = id;
        this.username = 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 + '\'' +
                '}';
    }
}

<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>

public class Configuration {
    private DataSource dataSource;
    
    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;
    }
}

public class MappedStatement {
    //sql语句id
    private String id;
    //sql语句
    private String sql;
    //输入参数类型
    private String parameterType;
    //返回参数类型
    private String resultType;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getSql() {
        return sql;
    }
    public void setSql(String sql) {
        this.sql = sql;
    }
    public String getParameterType() {
        return parameterType;
    }
    public void setParameterType(String parameterType) {
        this.parameterType = parameterType;
    }
    public String getResultType() {
        return resultType;
    }
    public void setResultType(String resultType) {
        this.resultType = resultType;
    }
}

public class Resources {
    //以流的形式读取配置文件
    public static InputStream getResourceAsStream(String path){
        InputStream resourceAsStream = Resources.class.getClassLoader().getResourceAsStream(path);
        return resourceAsStream;
    }
}

public class SqlSessionFactoryBuilder {
    public SqlSessionFactory build(InputStream inputStream) throws PropertyVetoException, DocumentException {
        //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(inputStream);

        //创建sqlSessionFactory工厂对象：生产sqlSession
        DefaultSqlSessionFactory defaultSqlSessionFactory = new DefaultSqlSessionFactory(configuration);
        return defaultSqlSessionFactory;
    }
}

public class XMLConfigBuilder {
    private Configuration configuration;

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

    
    public Configuration parseConfig(InputStream inputStream) throws DocumentException, PropertyVetoException {
        Document document = new SAXReader().read(inputStream);
        Element rootElement = document.getRootElement();
        List<Element> list = rootElement.selectNodes("//property");
        Properties properties = new Properties();
        list.forEach(element -> {
            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("username"));
        comboPooledDataSource.setPassword(properties.getProperty("password"));

        configuration.setDataSource(comboPooledDataSource);

        //解析<Mapper>标签
        List<Element> mapperList = rootElement.selectNodes("//mapper");
        mapperList.stream()
                .map(x -> x.attributeValue("resource"))
                .map(Resources::getResourceAsStream)
                .forEach(resourceAsStream -> {
                    XmlMapperBuilder xmlMapperBuilder = new XmlMapperBuilder(configuration);
                    try {
                        xmlMapperBuilder.parse(resourceAsStream);
                    } catch (DocumentException e) {
                        e.printStackTrace();
                    }
                });
        return configuration;
    }
}

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");
        list.forEach(element -> {
            String id = element.attributeValue("id");
            String parameterType = element.attributeValue("parameterType");
            String resultType = element.attributeValue("resultType");
            String sqlText = element.getTextTrim();
            MappedStatement mappedStatement = new MappedStatement();
            mappedStatement.setId(id);
            mappedStatement.setParameterType(parameterType);
            mappedStatement.setResultType(resultType);
            mappedStatement.setSql(sqlText);
            String key = namespace.concat(".").concat(id);
            configuration.getMappedStatementMap().put(key, mappedStatement);
        });
    }
}

public interface SqlSessionFactory {

    SqlSession openSession();
}

public class DefaultSqlSessionFactory implements SqlSessionFactory {

    private Configuration configuration;

    public DefaultSqlSessionFactory(Configuration configuration) {
        this.configuration = configuration;
    }
    @Override
    public SqlSession openSession() {
        return new DefaultSqlSession(configuration);
    }
}

public interface SqlSession {
    //查询所有
    <E> List<E> selectList(String mappedStatementId,Object... params) throws IllegalAccessException, IntrospectionException, InstantiationException, NoSuchFieldException, SQLException, InvocationTargetException, ClassNotFoundException;
    //根据条件
    <T> T selectOne(String mappedStatementId,Object... params) throws IllegalAccessException, ClassNotFoundException, IntrospectionException, InstantiationException, SQLException, InvocationTargetException, NoSuchFieldException;

    //为Dao接口生成代理实现类
    <T> T getMapper(Class<T> mapperClass);
}

public class DefaultSqlSession implements SqlSession {
    private Configuration configuration;
    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }
    @Override
    public <E> List<E> selectList(String mappedStatementId, Object... params) throws IllegalAccessException, IntrospectionException, InstantiationException, NoSuchFieldException, SQLException, InvocationTargetException, ClassNotFoundException {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(mappedStatementId);
        List<Object> objectList = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<E>) objectList;
    }
    @Override
    public <T> T selectOne(String mappedStatementId, Object... params) throws IllegalAccessException, ClassNotFoundException, IntrospectionException, InstantiationException, SQLException, InvocationTargetException, NoSuchFieldException {
        List<Object> objectList = selectList(mappedStatementId, params);
        if (objectList.size() == 1) {
            return (T) objectList.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多！");
        }
    }
    @Override
    public <T> T getMapper(Class<T> mapperClass) {
        //使用JDK动态代理来为Dao接口生成代理对象,并返回
        return (T) Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, ((proxy, method, args) -> {
            String methodName = method.getName();
            String className = method.getDeclaringClass().getName();
            String mappedStatementId = className.concat(".").concat(methodName);
            //获取被调用方法的返回值类型
            Type genericReturnType = method.getGenericReturnType();
            //判断是否进行了泛型类型参数化
            if (genericReturnType instanceof ParameterizedType){
                List<Object> objectList = selectList(mappedStatementId, args);
                return objectList;
            }
            return selectOne(mappedStatementId,args);
        }));
    }
}

public interface Executor {

    <E>List<E> query(Configuration configuration, MappedStatement mappedStatement,Object... params) throws SQLException, IntrospectionException, InvocationTargetException, IllegalAccessException, InstantiationException, ClassNotFoundException, NoSuchFieldException;
}

public class SimpleExecutor implements Executor {
    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws SQLException, IntrospectionException, InvocationTargetException, IllegalAccessException, InstantiationException, ClassNotFoundException, NoSuchFieldException {
        //注册驱动,获取连接
        Connection connection = configuration.getDataSource().getConnection();

        //获取sql语句：select * from user where id = #{id} and username = #{username}
        //转换sql语句：select * from user where id = ? and username = ?
        //转换的过程中,还需要对#{}里面的参数名称进行解析存储
        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 parameterType = mappedStatement.getParameterType();
        Class<?> parameterTypeClass = getClassType(parameterType);

        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);

        List<Object> objectList = new ArrayList<>();
        //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);
                // 字段的值
                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);
            }
            objectList.add(o);

        }
        return (List<E>) objectList;
    }

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

    
    private BoundSql getBoundSql(String sql) {
        //标记处理类：配置标记解析器来完成对占位符的解析处理工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
        //解析出来的sql
        String parseSql = genericTokenParser.parse(sql);
        //#{}里面解析出来的参数名称
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();

        BoundSql boundSql = new BoundSql(parseSql, parameterMappings);
        return boundSql;
    }
}

public class BoundSql {
    private String sqlText; //解析过后的sql

    private List<ParameterMapping> parameterMappingList = new ArrayList<>();

    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;
    }
}

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;
  }

  
  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.isEmpty()) {
      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class="lazy" data-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[] class="lazy" data-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 && class="lazy" data-src[start - 1] == '\\') {
        builder.append(class="lazy" data-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(class="lazy" data-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 && class="lazy" data-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(class="lazy" data-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(class="lazy" data-src, offset, end - offset);
            offset = end + closeToken.length();
            break;
          }
        }
        if (end == -1) {
          // close token was not found.
          builder.append(class="lazy" data-src, start, class="lazy" data-src.length - start);
          offset = class="lazy" data-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 < class="lazy" data-src.length) {
      builder.append(class="lazy" data-src, offset, class="lazy" data-src.length - offset);
    }
    return builder.toString();
  }
}

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;
    }
}

public interface TokenHandler {
  String handleToken(String content);
}

public class ParameterMappingTokenHandler implements TokenHandler {
	private List<ParameterMapping> parameterMappings = new ArrayList<>();

	// 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;
	}
}