自定义Mybatis简单实现方法

首先要明白mybatis为了解决jdbc存在的什么问题，最简单常见的就是以下几个

1. 数据库连接创建、释放频繁造成系统资源浪费，影响系统性能

2. SQL语句在代码中硬编码，不移维护

3. 预处理preparedStatement向占位符传参存在硬编码

4. 对结果集解析存在硬编码

一.自定义框架设计思路

使用端:

提供配置文件

SqlMapConfig.xml：存放数据源信息，引入mapper.xml

Mapper.xml：存放sql语句

自定义框架：

 

 

 二、代码

Pom引入插件

<dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.25</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和MapperdStatement

Configuration存放核心配置文件sqlMapConfig的数据
MapperdStatement存放mapper中的sql语句

public class Configuration {

    private DataSource dataSource;

    // key: statementid  value:封装好的mappedStatement对象
    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 {

    //id标识
    private String id;
    //返回值类型
    private String resultType;
    //参数值类型
    private String parameterType;
    //sql语句
    private String sql;
    //执行方法是select还是update
    private String type;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    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;
    }
}

 

XmlConfigBulider和XmlMapperBulider

使用dom4j对配置文件进行解析，封装到Configuration

public class XmlConfigBuilder {

    private Configuration configuration;

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

    /**
     * 该方法就是使用dom4j对配置文件进行解析，封装到Configuration
     */
    public Configuration parseConfig(InputStream inputStream) throws DocumentException, PropertyVetoException {

        Document document = new SAXReader().read(inputStream);
        //<configuration>
        Element rootElement = document.getRootElement();
        List<Element> list = rootElement.selectNodes("//property");
        Properties properties = new Properties();
        for (Element element : list) {
            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);

        //mapper.xml解析: 拿到路径--字节输入流---dom4j进行解析
        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;
    }
}

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");

        //解析select|insert|update|delete标签
        List<Element> elementList = rootElement.selectNodes("//select|insert|update|delete");

        for (Element element : elementList) {
            String type= element.getName();
            String id = element.attributeValue("id");
            String resultType = element.attributeValue("resultType");
            String paramterType = element.attributeValue("paramterType");
            String sqlText = element.getTextTrim();
            MappedStatement mappedStatement = new MappedStatement();
            mappedStatement.setId(id);
            mappedStatement.setResultType(resultType);
            mappedStatement.setParameterType(paramterType);
            mappedStatement.setSql(sqlText);
            mappedStatement.setType(type);
            String key = namespace+"."+id;
            configuration.getMappedStatementMap().put(key,mappedStatement);
        }
    }
}

sqlSession

创建sqlSessionFactory对象：工厂类：生产sqlSession:会话对象

创建sqlSession方法和实现类封装CRRD操作

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

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

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {

        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    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("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public boolean update(String statementId, Object... params) throws Exception {
        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.update(configuration, mappedStatement, params);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                // 底层都还是去执行JDBC代码 //根据不同情况，来调用selctList或者selectOne
                // 准备参数 1：statmentid :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();
                String statementId = className+"."+methodName;
                //获取方法类型是select还是增删改
                String type = configuration.getMappedStatementMap().get(statementId).getType();

                // 准备参数2：params:args
                if ("select".equals(type)){
                    // 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> objects = selectList(statementId, args);
                        return objects;
                    }
                    return selectOne(statementId,args);
                }else {
                    //返回值类型为void则表示是增删改操作
                    return update(statementId,args);
                }
            }
        });
        return (T) proxyInstance;
    }
}

public class SqlSessionFactoryBuilder {

    public SqlSessionFactory build(InputStream in) throws DocumentException, PropertyVetoException {
        // 第一：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(in);
        
        // 第二：创建sqlSessionFactory对象：工厂类：生产sqlSession:会话对象
        DefaultSqlSessionFactory defaultSqlSessionFactory = new DefaultSqlSessionFactory(configuration);

        return defaultSqlSessionFactory;
    }
}

public class DefaultSqlSessionFactory implements SqlSessionFactory {

    private Configuration configuration;

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

使用JDK动态代理来为Dao接口生成代理对象
代理对象调用接口中任意方法，都会执行invocationHandler接口实现类的invoke方法
invoke方法中：调用的还是sqlSession的crud方法

public class SimpleExecutor implements  Executor {

    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {

        // 获取数据库连接
        PreparedStatement preparedStatement = connectByJdbc(configuration, mappedStatement, params);

        // 执行sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);

        ArrayList<Object> objects = 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);
            }
            objects.add(o);
        }
        return (List<E>) objects;

    }

    @Override
    public boolean update(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception{
        // 获取数据库连接
        PreparedStatement preparedStatement = connectByJdbc(configuration, mappedStatement, params);
        // 执行sql
        return preparedStatement.execute();
    }

    //使用jdbc进行数据库连接
    private PreparedStatement connectByJdbc(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        // 1. 注册驱动，获取连接
        Connection connection = configuration.getDataSource().getConnection();

        // 2. 获取sql语句 : 将#｛｝转换成？占位符 ，转换的过程中，还需要对#{}里面的值进行解析存储
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        // 3.获取预处理对象：preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        // 4. 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);
        }
        return  preparedStatement;
    }


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

    }

    /**
     * 完成对#{}的解析工作：1.将#{}使用？进行代替，2.解析出#{}里面的值进行存储
     * @param sql
     * @return
     */
    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;
    }
}

 

解析类

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;
  }

  /**
   * 解析${}和#{}
   * @param text
   * @return
   * 该方法主要实现了配置文件、脚本等片段中占位符的解析、处理工作，并返回最终需要的数据。
   * 其中，解析工作由该方法完成，处理工作是由处理器handler的handleToken()方法来实现
   */
  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[] 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 && src[start - 1] == '\\') {
        builder.append(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(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 && 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(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(src, offset, end - offset);
            offset = end + closeToken.length();
            break;
          }
        }
        if (end == -1) {
          // close token was not found.
          builder.append(src, start, src.length - start);
          offset = 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 < src.length) {
      builder.append(src, offset, src.length - offset);
    }
    return builder.toString();
  }
}

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

    // context是参数名称 #{id} #{username}

    @Override
    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;
    }

}

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;
    }
}

Test

@Test
    public void test() throws Exception {
        InputStream resourceAsSteam = Resources.getResourceAsSteam("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsSteam);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //调用
        User user = new User();
        user.setId(1);
        user.setUsername("lucy");

        IUserDao userDao = sqlSession.getMapper(IUserDao.class);

        List<User> all = userDao.findAll();
        for (User user1 : all) {
            System.out.println(user1);
        }


    }

    @Test
    public void testAdd() throws Exception {
        InputStream resourceAsSteam = Resources.getResourceAsSteam("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsSteam);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //调用
        User user = new User();
        user.setId(3);
        user.setUsername("zhangsan");
        user.setPassword("123");
        user.setBirthday("1999-02-02");

        IUserDao userDao = sqlSession.getMapper(IUserDao.class);

        userDao.addUser(user);
    }

 

总结

基本上设计思路和mybatis一致，使用了
连接池：解决频繁创建释放数据库连接
配置文件：解决硬编码
反射、内省：解决手动封装返回结果集
jdk动态代理：隐藏DAO层接口实现类，返回接口的代理对象
应用了构建者模式，代理模式，工厂模式来实现自定义持久层框架完成

源码链接 > https://gitee.com/Hupochuan/i-persistence.git