一般情况下，都是在DAO类中使用JdbcTemplate，JdbcTemplate在XML配置文件中配置好，直接在DAO中注入即可。
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:p="http://www.springframework.org/schema/p"xmlns:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd"><context:component-scan base-package="com.ivy"/><context:property-placeholder location="classpath:jdbc.properties"/><bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"destroy-method="close"p:driverClassName="${jdbc.driverClassName}"p:url="${jdbc.url}"p:username="${jdbc.username}"p:password="${jdbc.password}"/><bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate"p:dataSource-ref="dataSource"/> </beans>
在Spring配置文件中配置DAO一般分为4个步骤：
- 定义DataSource
- 定义JdbcTemplate
- 声明一个抽象的bean，以便所有DAO复用配置JdbcTemplate属性的配置。
- 配置具体的DAO
基本数据操作
- 更改数据
尽量使用可绑定参数的SQL，以便数据库可以复用SQL的执行计划，提高数据库的执行效率。
- 返回数据库的表自增主键值
例如：
final String sqlString = "INSERT INTO t_forum(forum_name, forum_desc) VALUES (?, ?)";KeyHolder keyHolder = new GeneratedKeyHolder();jdbcTemplate.update(new PreparedStatementCreator() {@Overridepublic PreparedStatement createPreparedStatement(Connection conn)throws SQLException {PreparedStatement ps = conn.prepareStatement(sqlString);ps.setString(1, forum.getForumnName());ps.setString(2, forum.getForumnDesc());return ps;}}, keyHolder);forum.setForumnId(keyHolder.getKey().intValue());
- 批量更新
private final String BATCH_INSERT_SQL = "INSERT INTO t_forum(forum_name, forum_desc) VALUES (?, ?)";
public void addForums(final List<Forum> forums) {jdbcTemplate.batchUpdate(BATCH_INSERT_SQL, new BatchPreparedStatementSetter() {@Overridepublic void setValues(PreparedStatement ps, int index) throws SQLException {Forum forum = forums.get(index);ps.setString(1, forum.getForumName());ps.setString(2, forum.getForumDesc());}@Overridepublic int getBatchSize() {return forums.size();}});}
- 查询数据
Spring提供了RowCallbackHandler回调接口，通过该接口可以定义如何从结果集中获取数据。
单条结果集处理：
private final String SELECT_SQL = "SELECT forum_name, forum_desc FROM t_forum WHERE forum_id=?";
public Forum getForum(final int forumId) {final Forum forum = new Forum();jdbcTemplate.query(SELECT_SQL, new Object[]{forumId}, new RowCallbackHandler() {@Overridepublic void processRow(ResultSet rs) throws SQLException {forum.setForumId(forumId);forum.setForumDesc(rs.getString("forum_desc"));forum.setForumName(rs.getString("forum_name"));}});return forum;}
多条数据结果集的处理：
private final String SELECT_MULTI_SQL = "SELECT forum_id,forum_name, forum_desc FROM t_forum WHERE forum_id between ? and ?";
public List<Forum> getForums(final int fromId, final int toId) {final List<Forum> forums = new ArrayList<>();jdbcTemplate.query(SELECT_MULTI_SQL, new Object[]{fromId, toId}, new RowCallbackHandler() {@Overridepublic void processRow(ResultSet rs) throws SQLException {Forum forum = new Forum();forum.setForumId(rs.getInt("forum_id"));forum.setForumDesc(rs.getString("forum_desc"));forum.setForumName(rs.getString("forum_name"));forums.add(forum);}});return forums;}
使用RowMapper<T>处理结果集，RowMapper<T>更适合在多行结果集中使用：
private final String SELECT_MULTI_SQL = "SELECT forum_id,forum_name, forum_desc FROM t_forum WHERE forum_id between ? and ?";
public List<Forum> getForumsByRowMapper(final int fromId, final int toId) {return jdbcTemplate.query(SELECT_MULTI_SQL, new Object[]{fromId, toId}, new RowMapper<Forum>() {@Overridepublic Forum mapRow(ResultSet rs, int index) throws SQLException {Forum forum = new Forum();forum.setForumId(rs.getInt("forum_id"));forum.setForumDesc(rs.getString("forum_desc"));forum.setForumName(rs.getString("forum_name"));return forum;}});}
RowCallbackHandler vs RowMapper<T>
从功能上来说，RowCallbackHandler和RowMapper<T>并没有太大的区别，它们都是用于定义结果集行的读取逻辑，将ResultSet中的数据映射到对象或List中。
当处理大结果集时，如果使用RowMapper，结果集中的所有数据最终都会映射并汇总成一个List<T>对象，占用大量的JVM内存，甚至可直接引发OOM，这时，应该使用RowCallbackHandler接口，用processRow()方法内部处理结果集数据。
- 查询单值数据
int类型的单值查询接口：int queryForInt(String sql)
private final String COUNT_SQL = "SELECT COUNT(*) FROM t_forum"; public int getForumNum() {return jdbcTemplate.queryForInt(COUNT_SQL);}
long类型的单值查询接口：long queryForLong(String sql)
其他类型的单值查询接口：<T> T queryForObject(String sql, Class<T> requiredType);
使用RowMapper获取单值对象：
public class TopicDao {@Autowiredprivate JdbcTemplate jdbcTemplate;public double getReplyRate(int userId) {String sql = "SELECT topic_replies, topic_views FROM t_topic WHERE user_id=?";double rate = jdbcTemplate.queryForObject(sql, new Object[]{userId}, new RowMapper<Double>() {@Overridepublic Double mapRow(ResultSet rs, int index) throws SQLException {// TODO Auto-generated method stubint replies = rs.getInt("topic_replies");int views = rs.getInt("topic_views");if (views > 0) {return new Double((double)replies/views);} else {return new Double(0.0);}}});return rate;} }
调用存储过程
创建一个存储过程：
delimiter //CREATE PROCEDURE P_GET_TOPIC_NUM(IN in_user_id INT, OUT out_num INT) BEGINSELECT COUNT(*) INTO out_num FROM t_topic WHERE user_id=in_user_id; END // delimiter ;
public int getUserTopicNum(final int userId) {String sql = "{call P_GET_TOPIC_NUM(?,?)}";Integer num = jdbcTemplate.execute(sql, new CallableStatementCallback<Integer>() {@Overridepublic Integer doInCallableStatement(CallableStatement cs)throws SQLException, DataAccessException {// TODO Auto-generated method stubcs.setInt(1, userId);cs.registerOutParameter(2, Types.INTEGER);cs.execute();return cs.getInt(2);}});return num;}
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