简介
在 Mybatis3 的源码解析系列中，我们对其核心功能有了一定的了解，下面我们尝试简单写一下 Demo，让其有简单的 Mybatis 的一些核心功能，本篇是基础功能的搭建
Dome 编写
完整的工程已放到 GitHub 上：https://github.com/lw1243925457/MybatisDemo/tree/master/
本篇文章的代码对应的 Tag 是: V1
本篇的目标是完成 MapperProxy 和运行不带参数和无自定义返回类型的 SQL
测试代码如下：
public class SelfMybatisTest {
@Test public void test() { try(SelfSqlSession session = buildSqlSessionFactory()) { PersonMapper personMapper = session.getMapper(PersonMapper.class); personMapper.createTable(); personMapper.save(); List<Object> personList = personMapper.list(); for (Object person: personList) { System.out.println(person.toString()); } } }
public static SelfSqlSession buildSqlSessionFactory() { String JDBC_DRIVER = "org.h2.Driver"; String DB_URL = "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1"; String USER = "sa"; String PASS = "";
HikariConfig config = new HikariConfig(); config.setJdbcUrl(DB_URL); config.setUsername(USER); config.setPassword(PASS); config.setDriverClassName(JDBC_DRIVER); config.addDataSourceProperty("cachePrepStmts", "true"); config.addDataSourceProperty("prepStmtCacheSize", "250"); config.addDataSourceProperty("prepStmtCacheSqlLimit", "2048"); DataSource dataSource = new HikariDataSource(config);
SelfConfiguration configuration = new SelfConfiguration(dataSource);// configuration.getTypeHandlerRegistry().register(String[].class, JdbcType.VARCHAR, StringArrayTypeHandler.class); configuration.addMapper(PersonMapper.class); return new SelfSqlSession(configuration); }}
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如上所示，我们集成其他 DataSource，这里使用 HikariCP，然后初始化 Mapper，生成表、插入、查询
最终的结果如下：
初始化我们的 PersonMapper，最后输出查询的结果
add sql source: mapper.mapper.PersonMapper.listadd sql source: mapper.mapper.PersonMapper.saveadd sql source: mapper.mapper.PersonMapper.createTable
executorexecutorexecutor
[1, 1]
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基本达到了要求，下面开始讲解核心代码：
Mapper 初始化
我们的思路目前是：
1.SelfConfiguration 作为全局配置类，从中取得 DataSource 和 Mapper 相关的信息（目前是接口方法对应的 SQL 语句）
2.SelfConfiguration 构造函数保存 DataSource
3.SelfConfiguration 添加 Mapper 时，保存其中方式对应的 SQL 语句信息到 Map，方法的路径作为唯一标识
SelfConfiguration 相关的代码
public class SelfConfiguration {
private final DataSource dataSource; private final Map<String, SqlSource> sqlCache = new HashMap<>();
public SelfConfiguration(DataSource dataSource) { this.dataSource = dataSource; }
/** * Mapper添加 * 保存接口方法的SQL类型和方法 * 方法路径作为唯一的id * @param mapperClass mapper */ public void addMapper(Class<?> mapperClass) { final String classPath = mapperClass.getPackageName(); final String className = mapperClass.getName(); for (Method method: mapperClass.getMethods()) { final String id = StringUtils.joinWith("." ,classPath, className, method.getName()); for (Annotation annotation: method.getAnnotations()) { if (annotation instanceof Select) { addSqlSource(id, ((Select) annotation).value(), SqlType.SELECT); continue; } if (annotation instanceof Insert) { addSqlSource(id, ((Insert) annotation).value(), SqlType.INSERT); } } } }
private void addSqlSource(final String id, final String sql, final SqlType selectType) { System.out.println("add sql source: " + id); final SqlSource sqlSource = SqlSource.builder() .type(selectType) .sql(sql) .build(); sqlCache.put(id, sqlSource); }
public DataSource getDataSource() { return dataSource; }
public SqlSource getSqlSource(final String id) { if (sqlCache.containsKey(id)) { return sqlCache.get(id); } throw new RuntimeException("don't find mapper match: " + id); }}
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MapperProxy 生成
MapperProxy 从 SelfSqlSession 中进行获取，MapperProxy 中调用 Executor 的方法即可，比较简单
SelfSqlSession 主要是返回 MapperProxy
public class SelfSqlSession implements Closeable {
private final SelfConfiguration config;
public SelfSqlSession(SelfConfiguration configuration) { this.config = configuration; }
@Override public void close() { }
public <T> T getMapper(Class<?> mapperClass) { final MapperProxy<T> proxy = new MapperProxy(config); return (T) Proxy.newProxyInstance(mapperClass.getClassLoader(), new Class[] {mapperClass}, proxy); }}
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MapperProxy 简单调用下 Executor
public class MapperProxy<T> implements InvocationHandler {
private final SelfConfiguration config;
public MapperProxy(final SelfConfiguration configuration) { this.config = configuration; }
@Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return Executor.executor(config, proxy, method, args); }}
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SQL 语句执行
主要逻辑如下：
Executor 代码如下，获取数据库连接，StatementHandler 执行，ResultHandler 处理结果返回
public class Executor {
private static final StatementHandler statementHandler = new StatementHandler(); private static final ResultHandler resultHandler = new ResultHandler();
public static Object executor(SelfConfiguration config, Object proxy, Method method, Object[] args) throws SQLException { System.out.println("executor"); try (Connection conn = config.getDataSource().getConnection()) { ResultSet resultSet = statementHandler.prepare(conn, proxy, method, args, config); return resultHandler.parse(resultSet); } }}
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StetementHandler 主要是从 Config 从获取需要执行的 SQL 信息
目前比较简单，根据 SQL 类型，直接执行即可
public class StatementHandler {
public ResultSet prepare(Connection conn, Object proxy, Method method, Object[] args, SelfConfiguration config) throws SQLException { final String classPath = method.getDeclaringClass().getPackageName(); final String className = method.getDeclaringClass().getName(); final String methodName = method.getName(); final String id = StringUtils.joinWith(".", classPath, className, methodName); final SqlSource sqlSource = config.getSqlSource(id); if (sqlSource.getType().equals(SqlType.SELECT)) { return select(conn, sqlSource); } if (sqlSource.getType().equals(SqlType.INSERT)) { return insert(conn, sqlSource); } throw new RuntimeException("don't support this sql type"); }
private ResultSet insert(Connection conn, SqlSource sqlSource) throws SQLException { final Statement statement = conn.createStatement(); statement.execute(sqlSource.getSql()); return null; }
private ResultSet select(Connection conn, SqlSource sqlSource) throws SQLException { final Statement statement = conn.createStatement(); return statement.executeQuery(sqlSource.getSql()); }}
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ResultHandler 目前就是循环读取结果，然后返回
public class ResultHandler {
public List<Object> parse(ResultSet res) throws SQLException { if (res == null) { return null; }
final List<Object> list = new ArrayList<>(res.getFetchSize()); final ResultSetMetaData metaData = res.getMetaData(); while (res.next()) { final int count =metaData.getColumnCount(); final List<Object> val = new ArrayList<>(count); for (int i=1; i <= count; i++) { final String name = metaData.getColumnName(i); final Object value = res.getObject(name); val.add(value); } list.add(val); } return list; }}
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总结
本篇中搭建了 MyBatis Demo 的基础部分，除了结果返回有点不好看，其他有了点日常 MyBatis 的味道了，结果处理后面也会完善上去
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