java 回调 spring jdbc 查询模板

spring jdbc 查询模板  内部类的使用

感觉这种写法让代码显得很清晰，将固定的操作步骤制定成模板方法，通过使用者，自己来实现继承类来决定操作过程。


org.springframework.jdbc.core.RowMapper

public interface RowMapper<T> {
    T mapRow(ResultSet rs, int rowNum) throws SQLException; 

}

org.springframework.jdbc.core.RowMapperResultSetExtractor

public class RowMapperResultSetExtractor<T> implements ResultSetExtractor<List<T>> {

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

}

以下是模板类的操作过程：
org.springframework.jdbc.core.JdbcTemplate

public <T> List<T> query(String sql, RowMapper<T> rowMapper) throws DataAccessException {
		return query(sql, new RowMapperResultSetExtractor<T>(rowMapper));
	}


public <T> T query(final String sql, final ResultSetExtractor<T> rse) throws DataAccessException {
		Assert.notNull(sql, "SQL must not be null");
		Assert.notNull(rse, "ResultSetExtractor must not be null");
		if (logger.isDebugEnabled()) {
			logger.debug("Executing SQL query [" + sql + "]");
		}
		class QueryStatementCallback implements StatementCallback<T>, SqlProvider {
			public T doInStatement(Statement stmt) throws SQLException {
				ResultSet rs = null;
				try {
					rs = stmt.executeQuery(sql);
					ResultSet rsToUse = rs;
					if (nativeJdbcExtractor != null) {
						rsToUse = nativeJdbcExtractor.getNativeResultSet(rs);
					}
					return rse.extractData(rsToUse);
				}
				finally {
					JdbcUtils.closeResultSet(rs);
				}
			}
			public String getSql() {
				return sql;
			}
		}
		return execute(new QueryStatementCallback());
	}



//模板方法
public <T> T execute(StatementCallback<T> action) throws DataAccessException {
		Assert.notNull(action, "Callback object must not be null");

		Connection con = DataSourceUtils.getConnection(getDataSource());
		Statement stmt = null;
		try {
			Connection conToUse = con;
			if (this.nativeJdbcExtractor != null &&
					this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativeStatements()) {
				conToUse = this.nativeJdbcExtractor.getNativeConnection(con);
			}
			stmt = conToUse.createStatement();
			applyStatementSettings(stmt);
			Statement stmtToUse = stmt;
			if (this.nativeJdbcExtractor != null) {
				stmtToUse = this.nativeJdbcExtractor.getNativeStatement(stmt);
			}
			T result = action.doInStatement(stmtToUse);
			handleWarnings(stmt);
			return result;
		}
		catch (SQLException ex) {
			// Release Connection early, to avoid potential connection pool deadlock
			// in the case when the exception translator hasn't been initialized yet.
			JdbcUtils.closeStatement(stmt);
			stmt = null;
			DataSourceUtils.releaseConnection(con, getDataSource());
			con = null;
			throw getExceptionTranslator().translate("StatementCallback", getSql(action), ex);
		}
		finally {
			JdbcUtils.closeStatement(stmt);
			DataSourceUtils.releaseConnection(con, getDataSource());
		}
	}