本来对用法不是很想总结的,因为这些东西都是拿过来用,对原理不理解的我,觉得写这些总结就和网上铺天盖地的文章一样。但是昨天写了一篇发现想用的话其中还是有那么点问题的。所以就把JDBC template的常用总结再写一遍吧。
好啦,言归正传。
JDBC 配置
jdbc.properties # Properties file with JDBC and JPA settings. # # Applied by <context:property-placeholder location="jdbc.properties"/> from # various application context XML files (e.g., "applicationContext-*.xml"). # Targeted at system administrators, to avoid touching the context XML files. #------------------------------------------------------------------------------- # MySQL Settings #加载驱动 jdbc.driverClassName=com.mysql.jdbc.Driver #指定数据库、设置字符集、编码格式、自动连接 jdbc.url=jdbc:mysql://localhost:8080/?useUnicode=true&characterEncoding=UTF8&characterSetResults=UTF8&autoReconnect=true #数据库名字 jdbc.username=root #数据库密码 jdbc.password=123456 #mysqlmysql\u8FDE\u63A5\u5173\u95ED c3p0\u672A\u5173\u95ED\u95EE\u9898 c3p0.minPoolSize = 1 c3p0.maxPoolSize = 50 c3p0.initialPoolSize = 1 c3p0.maxIdleTime = 25000 c3p0.acquireIncrement = 1 c3p0.acquireRetryAttempts = 30 c3p0.acquireRetryDelay = 1000 c3p0.testConnectionOnCheckin = false #c3p0.automaticTestTable = t_c3p0 c3p0.idleConnectionTestPeriod = 18000 c3p0.checkoutTimeout=5000 # Properties that control the population of schema and data for a new data source #jdbc.initLocation=classpath:db/mysql/initDB.txt #jdbc.dataLocation=classpath:db/mysql/populateDB.txt # Property that determines which Hibernate dialect to use # (only applied with "applicationContext-hibernate.xml") #hibernate.dialect=org.hibernate.dialect.MySQLDialect # Property that determines which JPA DatabasePlatform to use with TopLink Essentials #jpa.databasePlatform=oracle.toplink.essentials.platform.database.MySQL4Platform # Property that determines which database to use with an AbstractJpaVendorAdapter
解读jdbc.properties
<?xml version="1.0" encoding="UTF-8"?> <!-- - DispatcherServlet application context for PetClinic's web tier. --> <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" xmlns:oxm="http://www.springframework.org/schema/oxm" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/oxm http://www.springframework.org/schema/oxm/spring-oxm-3.2.xsd"> <!-- c3p0 的数据库连接池 --> <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close"> <property name="driverClass" value="${jdbc.driverClassName}" /> <property name="jdbcUrl" value="${jdbc.url}" /> <property name="user" value="${jdbc.username}" /> <property name="password" value="${jdbc.password}" /> <property name="minPoolSize" value="${c3p0.minPoolSize}"/> <property name="maxPoolSize" value="${c3p0.maxPoolSize}"/> <property name="initialPoolSize" value="${c3p0.initialPoolSize}"/> <property name="maxIdleTime" value="${c3p0.maxIdleTime}"/> <property name="acquireIncrement" value="${c3p0.acquireIncrement}"/> <property name="acquireRetryAttempts" value="${c3p0.acquireRetryAttempts}"/> <property name="acquireRetryDelay" value="${c3p0.acquireRetryDelay}"/> <property name="testConnectionOnCheckin" value="${c3p0.testConnectionOnCheckin}"/> <!-- <property name="automaticTestTable" value="${c3p0.automaticTestTable}"/> --> <property name="idleConnectionTestPeriod" value="${c3p0.idleConnectionTestPeriod}"/> <property name="checkoutTimeout" value="${c3p0.checkoutTimeout}"/> </bean> <context:property-placeholder location="classpath:/conf/jdbc.properties" ignore-unresolvable="true" /> </beans>
说明
为了方便使用同样可以定义一个父类来初始化jdbcTemplate模板。
public abstract class AbstractDao { protected DataSource dataSource; protected JdbcTemplate jdbcTemplate; public DataSource getDataSource() { return this.dataSource; } @Autowired public void setDataSource(DataSource dataSource) { this.dataSource = dataSource; this.jdbcTemplate=new JdbcTemplate(dataSource); } }
CURD操作
这里面主要讲一下返回对象时的做法,其余的CURD不具体讲解了,大家肯定都知道了。
所以直接拿代码来看区别吧。
传统的jdbc返回对象、List<Vo>的形式
/** * 获取xx * @param status * @return List<UserTypeVO> */ public List<UserTypeVO> getUtypeList(int status){ String sql; MapSqlParameterSource paramSource = new MapSqlParameterSource(); if(status==-1){ sql = "select * from type order by display_order asc"; }else{ sql = "select * from type where status=:status order by display_order asc"; paramSource.addValue("status",status);} try { SqlRowSet ret = this.namedJdbcTemplate.queryForRowSet(sql,paramSource); List<UserTypeVO> list = new ArrayList<UserTypeVO>(); while (ret.next()) { UserTypeVO utype_vo=new UserTypeVO(); utype_vo.setId(ret.getInt("id")); utype_vo.setDisplay_order(ret.getInt("display_order")); utype_vo.setUtype(ret.getInt("utype")); utype_vo.setUtype_name(ret.getString("utype_name")); utype_vo.setIf_change(ret.getInt("if_change")); utype_vo.setStatus(ret.getInt("status")); list.add(utype_vo); } return list; } catch (Exception e) { e.printStackTrace(); } return null; }
说明
这个是很早jdbc使用方法,我们可以看出,使用queryForRowSet将数据查出之后,判断是否一直有值,有的话就一个个将值按id取出,set到对应的字段之中。
假设,我有100个字段,那么是不是要写100遍这样的代码?
所以,现在下面的这种方式,帮你做了回答,我们完全可以不管这些,只管SQL就行了。
自动组装对象、List<V0>示例
public class Dao extends AbstractDao{ private BeanPropertyRowMapper<UserVo> recRowMapper = new BeanPropertyRowMapper<UserVo>(UserVo.class) /** * 获取xx信息 */ @Override public List<UserVo> getUserVos(int status){ List<UserVo> UserVos = new ArrayList<UserVo>(); try { String sql = "SELECT r.id, r.uid, r.display_order, r.status, r.create_time, r.update_time " + " FROM " + AppConstant.DATABASE_SCHEMA_APP_BB_APP + "." + AppConstant.DATABASE_TABLE_USER + " r WHERE r.status =:status AND u.uid = r.uid order by r.display_order asc "; MapSqlParameterSource paramSource = new MapSqlParameterSource(); paramSource.addValue("status", status); recommendUserVos = this.namedJdbcTemplate.query(sql, paramSource, recRowMapper); } catch (Exception e) { log.debug("there is an error on getDaoImpl sql or param please check in." + e); } return UserVos; } }
说明
两端代码对比得出、同样的返回List<Vo>的类型,下面代码就没有长长的组装对象的语句。为什么呢?
答案就是:1.它使用了 private BeanPropertyRowMapper<UserVo> recRowMapper = new BeanPropertyRowMapper<UserVo>(UserVo.class);这样一个方法,来自动装配对象。
那么它根据什么知道如何装配的呢?首先我们知道UserVo这里有哪些属性,同时我们结合了jdbc中this.namedJdbcTemplate.query(sql, paramSource, recRowMapper);这个方法,看方法中有一个参数为recRowMapper。由此得知是它们起了作用,在模板的帮助下,将其自动转换。
注意因为在自动装配的时候,一定要通过一个关键字才能拿到对应的值,那么如何知道那个关键字就是数据库中的呢?所以这时我们就需要将bean中的属性名字,和数据库中字段的名字完全一致,确保取到唯一准确值,这样才能对应封装为正确的Vo,或者List<Vo>,否则会报错的哦~
结束语:
这次总结,只总结了这个小用法,至于内部具体是如何实现的,喜欢的人可以自己看看源代码。