JdbcTemplate源码解析

JdbcTemplate源码解析

先写一个测试代码

package jdbc;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import org.springframework.beans.factory.support.DefaultListableBeanFactory;import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;import org.springframework.core.io.ClassPathResource;import org.springframework.jdbc.core.JdbcTemplate;import org.springframework.jdbc.core.RowCallbackHandler;public class JDBCTest { public static void main(String[] args) { //加载spring ClassPathResource resource = new ClassPathResource( "applicationContext-common2.xml"); DefaultListableBeanFactory factory = new DefaultListableBeanFactory(); XmlBeanDefinitionReader bdf = new XmlBeanDefinitionReader(factory); bdf.loadBeanDefinitions(resource); //获得jdbctemplate JdbcTemplate jt = (JdbcTemplate) factory.getBean("jdbcTemplate"); String sql = "select * from dream where personid=?"; final List> list = new ArrayList>(); // 一定要用final定义 Object[] params = new Object[] { 1 }; //调用query方法 //注意 query有三个参数 sql params还有一个RowCallbackHandler jt.query(sql, params, new RowCallbackHandler() { @Override public void processRow(ResultSet rs) throws SQLException { Map u = new HashMap(); u.put("id", rs.getString("id")); u.put("description", rs.getString("description")); list.add(u); } }); for ( Map u :list) { System.out.println(u.get("description")); } //HERE IS A SIMPLE EXAMPLE //EXAMPLE EXAMPLE }}

前期构造方法的调用

我们能追踪到JDBCTemplate的query方法,如下:

//JDBCTemplate.java public void query(String sql, Object[] args, RowCallbackHandler rch) throws DataAccessException { query(sql, newArgPreparedStatementSetter(args), rch); }

关于statement与preparedstatement的区别,我默认大家都明白。

算了还是写出来吧

String name="董磊峰2";

int id=18;

String sql="insert into admininfo (Aname,Aid) values(?,?)";

PreparedStatement st=conn.prepareStatement(sql);

st.setString(1, name);         //给第一个栏位注入String型的数值name  这个不是从0开始

st.setInt(2, id);

st.execute();

我们使用sql生成preparedstatement,再把参数传递进去。

newArgPreparedStatementSetter方法返回了一个ArgPreparedStatementSetter类,而ArgPreparedStatementSetter方法实现了PreparedStatementSetter

public interface PreparedStatementSetter { /** * Set parameter values on the given PreparedStatement. * @param ps the PreparedStatement to invoke setter methods on * @throws SQLException if a SQLException is encountered * (i.e. there is no need to catch SQLException) */ void setValues(PreparedStatement ps) throws SQLException; }

很清楚,PreparedStatementSetter就是写参数的嘛

干的事情就类似于上面的PreparedStatement的setString,setInt

//JDBCTemplate.java

public void query(String sql, PreparedStatementSetter pss, RowCallbackHandler rch) throws DataAccessException {

query(sql, pss, new RowCallbackHandlerResultSetExtractor(rch));

}

这个RowCallbackHandlerResultSetExtractor是个干什么的?大家看看它的构造方法包含我们在前面的RowCallbackHandler。

猜也能猜出来,这个是对最后处理逻辑的调用。

举个最简单的例子,我们自己写的RowCallbackHandler的参数是一个ResultSet,等到循环处理多条数据的时候,就得循环的调用processRow,那么在哪里调用呢?

在RowCallbackHandlerResultSetExtractor里

/** * Adapter to enable use of a RowCallbackHandler inside a ResultSetExtractor. *

Uses a regular ResultSet, so we have to be careful when using it: * We don't use it for navigating since this could lead to unpredictable consequences. */ private static class RowCallbackHandlerResultSetExtractor implements ResultSetExtractor