Fescar - RM ExecuteTemplate介绍

开篇

 这篇文章的目的是介绍Fescar的RM模块中的ExecuteTemplate的代码，ExecuteTemplate作为StatementProxy当中真正执行SQL操作的模块，在Proxy和Executor的串联中起到承上启下的作用。

 调用链上按照DataSourceProxy->ConnectionProxy->StatementProxy->Executor的顺序进行。

ExecuteTemplate源码介绍

public class StatementProxy extends AbstractStatementProxy {

    @Override
    public ResultSet executeQuery(String sql) throws SQLException {
        this.targetSQL = sql;
        return ExecuteTemplate.execute(this, new StatementCallback() {
            @Override
            public ResultSet execute(Statement statement, Object... args) 
             throws SQLException {
                return statement.executeQuery((String) args[0]);
            }
        }, sql);
    }

    @Override
    public int executeUpdate(String sql) throws SQLException {
        this.targetSQL = sql;
        return ExecuteTemplate.execute(this, new StatementCallback() {
            @Override
            public Integer execute(Statement statement, Object... args) 
             throws SQLException {
                return statement.executeUpdate((String) args[0]);
            }
        }, sql);
    }
}

说明：

• StatementProxy通过执行executeQuery和executeUpdate执行具体的SQL语句。

public class ExecuteTemplate {
    public static  T execute(StatementProxy statementProxy,
                                                     StatementCallback statementCallback,
                                                     Object... args) throws SQLException {
        return execute(null, statementProxy, statementCallback, args);
    }



    public static  T execute(SQLRecognizer sqlRecognizer,
                                                     StatementProxy statementProxy,
                                                     StatementCallback statementCallback,
                                                     Object... args) throws SQLException {

        if (!RootContext.inGlobalTransaction()) {
            // Just work as original statement
            return statementCallback.execute(statementProxy.getTargetStatement(), args);
        }

        if (sqlRecognizer == null) {
            sqlRecognizer = SQLVisitorFactory.get(
                statementProxy.getTargetSQL(),
                statementProxy.getConnectionProxy().getDbType());
        }
        Executor executor = null;
        if (sqlRecognizer == null) {
            executor = new PlainExecutor(statementProxy, statementCallback);
        } else {
            switch (sqlRecognizer.getSQLType()) {
                case INSERT:
                    executor = new InsertExecutor(statementProxy, statementCallback, sqlRecognizer);
                    break;
                case UPDATE:
                    executor = new UpdateExecutor(statementProxy, statementCallback, sqlRecognizer);
                    break;
                case DELETE:
                    executor = new DeleteExecutor(statementProxy, statementCallback, sqlRecognizer);
                    break;
                case SELECT_FOR_UPDATE:
                    executor = new SelectForUpdateExecutor(statementProxy, statementCallback, sqlRecognizer);
                    break;
                default:
                    executor = new PlainExecutor(statementProxy, statementCallback);
                    break;
            }
        }
        T rs = null;
        try {
            rs = executor.execute(args);

        } catch (Throwable ex) {
            if (ex instanceof SQLException) {
                throw (SQLException) ex;
            } else {
                // Turn everything into SQLException
                new SQLException(ex);
            }
        }
        return rs;
    }
}

说明：

• ExecuteTemplate内部根据SQL执行类型不同分为InsertExecutor、UpdateExecutor、DeleteExecutor、SelectForUpdateExecutor、PlainExecutor。
• InsertExecutor负责执行insert的SQL。
• UpdateExecutor负责执行update的SQL。
• DeleteExecutor负责执行delete的SQL。
• SelectForUpdateExecutor负责执行select for update操作的SQL。

期待

 后续进一步分析不同的Executor的执行逻辑，很快就要接近RM的核心逻辑。

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