spring jdbc源码分析

分别构建三个参数：
PreparedStatementCreator :对PreparedStatement进行创建
PreparedStatementSetter :对PreparedStatement进行赋值
ResultSetExtractor :对ResultSet结果进行处理
1.对PreparedStatement进行创建

private static class SimplePreparedStatementCreator implements PreparedStatementCreator, SqlProvider

SimplePreparedStatementCreator 包装了用户传来的sql语句。
创建PreparedStatement对象的主要方法：

public PreparedStatement createPreparedStatement(Connection con) throws SQLException {
			return con.prepareStatement(this.sql);
		}

2.PreparedStatementSetter 的构建，对PreparedStatement进行赋值

class ArgPreparedStatementSetter implements PreparedStatementSetter, ParameterDisposer

ArgPreparedStatementSetter里的核心方法：

public void setValues(PreparedStatement ps) throws SQLException {
		if (this.args != null) {
			for (int i = 0; i < this.args.length; i++) {
				Object arg = this.args[i];
				if (arg instanceof SqlParameterValue) {
					SqlParameterValue paramValue = (SqlParameterValue) arg;
					StatementCreatorUtils.setParameterValue(ps, i + 1, paramValue, paramValue.getValue());
				}
				else {
					StatementCreatorUtils.setParameterValue(ps, i + 1, SqlTypeValue.TYPE_UNKNOWN, arg);
				}
			}
		}
	}

3.ResultSetExtractor的构建，对ResultSet结果进行处理：

ParameterizedRowMapper<T> extends RowMapper 

RowMapperResultSetExtractor implements ResultSetExtractor

RowMapperResultSetExtractor 对RowMapper进行了包装，RowMapperResultSetExtractor 里的核心方法：

public Object extractData(ResultSet rs) throws SQLException {
		List results = (this.rowsExpected > 0 ? new ArrayList(this.rowsExpected) : new ArrayList());
		int rowNum = 0;
		while (rs.next()) {
			results.add(this.rowMapper.mapRow(rs, rowNum++));
		}
		return results;
	}

从extractData方法里可以看出,最后回调的是RowMapper里的方法mapRow,所以我们可以对这个方法进行实现。

例如：

class MyRowMapper implements ParameterizedRowMapper<Child> {
		public Child mapRow(ResultSet resultSet, int i) throws SQLException {
			ParentManager mgr = (ParentManager) Platform.getInstance().getBean(ParentManager.BEAN_ID);			
			Child child = new Child();
			child.setId(resultSet.getString("id"));
			child.setName(resultSet.getString("name"));
			child.setContent(resultSet.getString("content"));
			child.setParent(mgr.get(resultSet.getLong("parentid")));
			return child;
		}
	}

三个对象构建出来以后，最后会调用方法：

public Object query(
			PreparedStatementCreator psc, final PreparedStatementSetter pss, final ResultSetExtractor rse)

public Object query(
			PreparedStatementCreator psc, final PreparedStatementSetter pss, final ResultSetExtractor rse)
			throws DataAccessException {

		Assert.notNull(rse, "ResultSetExtractor must not be null");
		logger.debug("Executing prepared SQL query");

		return execute(psc, new PreparedStatementCallback() {
			public Object doInPreparedStatement(PreparedStatement ps) throws SQLException {
				ResultSet rs = null;
				try {
					if (pss != null) {
//对PreparedStatement 的参数进行设置
						pss.setValues(ps);
					}
					rs = ps.executeQuery();
					ResultSet rsToUse = rs;
					if (nativeJdbcExtractor != null) {
						rsToUse = nativeJdbcExtractor.getNativeResultSet(rs);
					}
//对ResultSet结果进行处理，最终返回一个List集合对象
					return rse.extractData(rsToUse);
				}
				finally {
					JdbcUtils.closeResultSet(rs);
					if (pss instanceof ParameterDisposer) {
						((ParameterDisposer) pss).cleanupParameters();
					}
				}
			}
		});
	}