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