mybatis源码笔记

mybatis设计总览

目录结构：

通过配置文件，获取SqlSessionFactory

XMLConfigBuilder 解析配置文件，获取SqlSessionFactory

    private static SqlSessionFactory getSqlSessionFactory() {
        String resource = "mybatis/mybatis-config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        return sqlSessionFactory;
    }

mybatis-config.xml，数据源和mapper配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <typeAliases>
        <typeAlias type="entity.User" alias="User"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost/mybatisLearn"/>
                <property name="username" value="mysql"/>
                <property name="password" value="mysql"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>

</configuration>

SqlSessionFactory的属性和方法

    private final Configuration configuration;

    public SqlSession openSession() {
        return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), (TransactionIsolationLevel)null, false);
    }

    private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
        Transaction tx = null;

        DefaultSqlSession var8;
        try {
            Environment environment = this.configuration.getEnvironment();
            TransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(environment);
            tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
            Executor executor = this.configuration.newExecutor(tx, execType);
            var8 = new DefaultSqlSession(this.configuration, executor, autoCommit);
        } catch (Exception var12) {
            this.closeTransaction(tx);
            throw ExceptionFactory.wrapException("Error opening session.  Cause: " + var12, var12);
        } finally {
            ErrorContext.instance().reset();
        }

        return var8;
    }

SqlSessionFactory的功能就是获取SqlSession，默认实现类DefaultSqlSession，DefaultSqlSession可以执行curd，也可以通过获取mapper来执行curd

DefaultSqlSession是直接执行sql操作数据库，mapper是通过接口方法（实际上还是要映射sql）

sqlSession可以指定事务隔离级别

TransactionIsolationLevel：

    NONE(0),
    READ_COMMITTED(2),
    READ_UNCOMMITTED(1),
    REPEATABLE_READ(4),
    SERIALIZABLE(8);

DefaultSqlSession的属性和方法

    private Configuration configuration;
    private Executor executor;
    private boolean autoCommit;
    private boolean dirty;
    private List<Cursor<?>> cursorList;

    public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
        try {
            MappedStatement ms = this.configuration.getMappedStatement(statement);
            this.executor.query(ms, this.wrapCollection(parameter), rowBounds, handler);
        } catch (Exception var9) {
            throw ExceptionFactory.wrapException("Error querying database.  Cause: " + var9, var9);
        } finally {
            ErrorContext.instance().reset();
        }

    }

    public int update(String statement, Object parameter) {
        int var4;
        try {
            this.dirty = true;
            MappedStatement ms = this.configuration.getMappedStatement(statement);
            var4 = this.executor.update(ms, this.wrapCollection(parameter));
        } catch (Exception var8) {
            throw ExceptionFactory.wrapException("Error updating database.  Cause: " + var8, var8);
        } finally {
            ErrorContext.instance().reset();
        }

        return var4;
    }

   public void commit(boolean force) {
        try {
            this.executor.commit(this.isCommitOrRollbackRequired(force));
            this.dirty = false;
        } catch (Exception var6) {
            throw ExceptionFactory.wrapException("Error committing transaction.  Cause: " + var6, var6);
        } finally {
            ErrorContext.instance().reset();
        }

    }

   public <T> T getMapper(Class<T> type) {
        return this.configuration.getMapper(type, this);
    }

Configuration是对mybatis-config.xml解析后的封装，配置文件的节点对应Configuration的属性

例如：<environment 对应 protected Environment environment;

注意Executor是在SqlSessionFactory中就获取的：Executor executor = this.configuration.newExecutor(tx, execType);

实际上调用的configuration中的方法：

    public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
        executorType = executorType == null ? this.defaultExecutorType : executorType;
        executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
        Object executor;
        if (ExecutorType.BATCH == executorType) {
            executor = new BatchExecutor(this, transaction);
        } else if (ExecutorType.REUSE == executorType) {
            executor = new ReuseExecutor(this, transaction);
        } else {
            executor = new SimpleExecutor(this, transaction);
        }

        if (this.cacheEnabled) {
            executor = new CachingExecutor((Executor)executor);
        }

        Executor executor = (Executor)this.interceptorChain.pluginAll(executor);
        return executor;
    }

根据参数生成对应的executor的实现

看看抽象类BaseExecutor的方法：

    protected Transaction transaction;
    protected Executor wrapper;
    protected ConcurrentLinkedQueue<BaseExecutor.DeferredLoad> deferredLoads;
    protected PerpetualCache localCache;
    protected PerpetualCache localOutputParameterCache;
    protected Configuration configuration;
    protected int queryStack = 0;
    private boolean closed;

   public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
        ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
        if (this.closed) {
            throw new ExecutorException("Executor was closed.");
        } else {
            if (this.queryStack == 0 && ms.isFlushCacheRequired()) {
                this.clearLocalCache();
            }

            List list;
            try {
                ++this.queryStack;
                list = resultHandler == null ? (List)this.localCache.getObject(key) : null;
                if (list != null) {
                    this.handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
                } else {
                    list = this.queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
                }
            } finally {
                --this.queryStack;
            }

            if (this.queryStack == 0) {
                Iterator i$ = this.deferredLoads.iterator();

                while(i$.hasNext()) {
                    BaseExecutor.DeferredLoad deferredLoad = (BaseExecutor.DeferredLoad)i$.next();
                    deferredLoad.load();
                }

                this.deferredLoads.clear();
                if (this.configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
                    this.clearLocalCache();
                }
            }

            return list;
        }
    }

看看其中的SimpleExecutor：

    public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
        Statement stmt = null;

        int var6;
        try {
            Configuration configuration = ms.getConfiguration();
            StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, (ResultHandler)null, (BoundSql)null);
            stmt = this.prepareStatement(handler, ms.getStatementLog());
            var6 = handler.update(stmt);
        } finally {
            this.closeStatement(stmt);
        }

        return var6;
    }

    public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
        Statement stmt = null;

        List var9;
        try {
            Configuration configuration = ms.getConfiguration();
            StatementHandler handler = configuration.newStatementHandler(this.wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
            stmt = this.prepareStatement(handler, ms.getStatementLog());
            var9 = handler.query(stmt, resultHandler);
        } finally {
            this.closeStatement(stmt);
        }

        return var9;
    }

还是调用的configuration的方法

处理sql相关的类

MappedStatement,获取BoundSql

    public BoundSql getBoundSql(Object parameterObject) {
        BoundSql boundSql = this.sqlSource.getBoundSql(parameterObject);
        List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
        if (parameterMappings == null || parameterMappings.isEmpty()) {
            boundSql = new BoundSql(this.configuration, boundSql.getSql(), this.parameterMap.getParameterMappings(), parameterObject);
        }

        Iterator i$ = boundSql.getParameterMappings().iterator();

        while(i$.hasNext()) {
            ParameterMapping pm = (ParameterMapping)i$.next();
            String rmId = pm.getResultMapId();
            if (rmId != null) {
                ResultMap rm = this.configuration.getResultMap(rmId);
                if (rm != null) {
                    this.hasNestedResultMaps |= rm.hasNestedResultMaps();
                }
            }
        }

        return boundSql;
    }

BoundSql，获取执行的sql

    private String sql;
    private List<ParameterMapping> parameterMappings;
    private Object parameterObject;
    private Map<String, Object> additionalParameters;
    private MetaObject metaParameters;

BaseStatementHandler,获取Statement

    public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
        ErrorContext.instance().sql(this.boundSql.getSql());
        Statement statement = null;

        try {
            statement = this.instantiateStatement(connection);
            this.setStatementTimeout(statement, transactionTimeout);
            this.setFetchSize(statement);
            return statement;
        } catch (SQLException var5) {
            this.closeStatement(statement);
            throw var5;
        } catch (Exception var6) {
            this.closeStatement(statement);
            throw new ExecutorException("Error preparing statement.  Cause: " + var6, var6);
        }
    }

SimpleStatementHandler,获取Statement

   protected Statement instantiateStatement(Connection connection) throws SQLException {
        return this.mappedStatement.getResultSetType() != null ? connection.createStatement(this.mappedStatement.getResultSetType().getValue(), 1007) : connection.createStatement();
    }

    public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
        String sql = this.boundSql.getSql();
        statement.execute(sql);
        return this.resultSetHandler.handleResultSets(statement);
    }

最终还是JDBC的那一套。