Common Dbutils是操作数据库的组件，对传统操作数据库的类进行二次封装，可以把结果集转化成List。
DBUtils包括3个包：
org.apache.commons.dbutils
org.apache.commons.dbutils.handlers
org.apache.commons.dbutils.wrappers
DBUtils封装了对JDBC的操作，简化了JDBC操作，可以少写代码。
org.apache.commons.dbutils
DbUtils 关闭链接等操作
QueryRunner 进行查询的操作
org.apache.commons.dbutils.handlers
ArrayHandler ：将ResultSet中第一行的数据转化成对象数组
ArrayListHandler将ResultSet中所有的数据转化成List，List中存放的是Object[]
BeanHandler ：将ResultSet中第一行的数据转化成类对象
BeanListHandler ：将ResultSet中所有的数据转化成List，List中存放的是类对象
ColumnListHandler ：将ResultSet中某一列的数据存成List，List中存放的是Object对象
KeyedHandler ：将ResultSet中存成映射，key为某一列对应为Map。Map中存放的是数据
MapHandler ：将ResultSet中第一行的数据存成Map映射
MapListHandler ：将ResultSet中所有的数据存成List。List中存放的是Map
ScalarHandler ：将ResultSet中一条记录的其中某一列的数据存成Object
org.apache.commons.dbutils.wrappers
SqlNullCheckedResultSet ：对ResultSet进行操作，改版里面的值
StringTrimmedResultSet ：去除ResultSet中中字段的左右空格。
QueryRunner
构造 QueryRunner ： 有两种方法来构造QueryRunner 一种是无参数的 一种是有DataSource类型参数的构造方法
1:QueryRunner() 2:QueryRunner(javax.sql.DataSource ds)
这里使用DataSource 来构造它 使用连接池来构造它的好处就是 我们无需管Connection 对象的创建与关闭了,后面调用QueryRunner对象的方法也无需传入Connection对象了
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/**
* dbcp连接池的用法
*/
public class DBUtils {
private static Properties properties;
private static DataSource dataSource;
private static Connection conn;
static {
try {
properties = new Properties();
//载入dbcp的配置文件
properties.load(DBUtils.class.
.getResourceAsStream("/dbcpconfig.properties"));
//创建个BasicDataSourceFactory对象用于创建连接池对象
BasicDataSourceFactory b = new BasicDataSourceFactory();
//把properties对象设置给BasicDataSourceFactory
dataSource = b.createDataSource(properties);
} catch (Exception e) {
e.printStackTrace();
}
}
public static DataSource getdataSource() {
return dataSource;
}
}
注意：需要导入dbcp连接池的jar commons-dbcp-1.2.1.jar 和所依赖的 commons-pool-1.2.jar 和commons-collections-3.1.jar
这样我们就可以构造个queryRunner对象了
QueryRunner queryRunner = new QueryRunner(DBUtils.getdataSource());
QueryRunner 主要方法 ：
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//更新一列
queryRunner.update("update Users set username=?,password=? where id = ?", new String[]{"11","22","1"});
//删除一列
queryRunner.update("delete from Users where id =?", 1);
如果要 使用 QueryRunner的查询方法 也就是query()方法的话 那么就需要有对象来接收查询出来的ResultSet
用什么来接收呢？ 要用到 实现ResultSetHandler 接口的类
1. BeanHandler 返回个entitybean 对象
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//指定返回哪个 entitybean
ResultSetHandler rsh = new BeanHandler(Users.class);
QueryRunner queryRunner = new QueryRunner(DBUtils.getdataSource());
Users users = (Users) queryRunner.query("select * from Users where id=?",2, rsh);
System.out.println(users.getUsername());
2. BeanListHandler 返回个List List里装的是entitybean 对象
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QueryRunner queryRunner = new QueryRunner(DBUtils.getdataSource());
ResultSetHandler rsh = new BeanListHandler(Users.class);
List<Users> list = (List) queryRunner.query(
"select * from Users ", rsh);
for(Users user:list){
System.out.println(user.getUsername());
}
3. ArrayListHandler 返回List 对象 list里装的为Object数组
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QueryRunner queryRunner = new QueryRunner(DBUtils.getdataSource());
// 使用ArrayListHandler 实现类来存放结果会返回ArrayList对象
ResultSetHandler rsh = new ArrayListHandler();
//list里装的是对象数组
List<Object[]> list = (List) queryRunner.query(
"select * from Users ", rsh);
for(Object[] user:list) {
for(Object obj:user)
{
System.out.println(obj);
}
}
4. ColumnListHandler 返回List 对象
注意: 构造 ColumnListHandler() 对象时候如果 是无参数的话 像这样 ResultSetHandler rsh = new ColumnListHandler(); 查询出来的List 里放的类型为主键的类型 值为主键的值;
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ResultSetHandler rsh = new ColumnListHandler();
List<Integer> list = (List) queryRunner.query(
"select * from Users ", rsh);
//System.out.println(list.get(0).getClass().getSimpleName());
for(Integer in:list){
System.out.println(in);
}
构造 ColumnListHandler() 对象时候如果 是有参数的话 ，像这样 ResultSetHandler rsh = new ColumnListHandler(主键值); 那么查询出来的List 里放的是就是这个主键对应的一行的记录;
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ResultSetHandler rsh = new ColumnListHandler(2);
List<String> list = (List) queryRunner.query(
"select * from Users ", rsh);
for(String in:list){
System.out.println(in);
}
5. KeyedHandler 根据键返回Map
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ResultSetHandler rsh = new KeyedHandler();
//map里装的key为主键的值 value 为主键对应的那行记录名称和记录
Map map = (Map) queryRunner.query(
"select id,username,password from Users ", rsh);
//根据主键值出去那一列
// Map t = (Map) map.get(2);
System.out.println(map.get(2));
6. MapHandler 根据键返回Map
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QueryRunner queryRunner = new QueryRunner(DBUtils.getdataSource());
ResultSetHandler rsh = new MapHandler();
Map map = (Map) queryRunner.query(
"select * from Users ", rsh);
System.out.println(map);
下面给出一个完整的例子，建立三个Java文件
BeanListExample.java
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package com.sy;
import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.List;
public class BeanListExample {
public static void main(String[] args) {
Connection conn = null;
String url = "jdbc:mysql://localhost:3306/people";
String jdbcDriver = "com.mysql.jdbc.Driver";
String user = "root";
String password = "hicc";
DbUtils.loadDriver(jdbcDriver);
try {
conn = DriverManager.getConnection(url, user, password);
QueryRunner qr = new QueryRunner();
List results = (List) qr.query(conn, "select id,name from guestbook", new BeanListHandler(Guestbook.class));
for (int i = 0; i < results.size(); i++) {
Guestbook gb = (Guestbook) results.get(i);
System.out.println("id:" + gb.getId() + ",name:" + gb.getName());
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
DbUtils.closeQuietly(conn);
}
}
}
Guestbook.java
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package com.sy;
public class Guestbook {
private Integer id;
private String name;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
MapListExample.java
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package com.sy;
import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.MapListHandler;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;
public class MapListExample {
public static void main(String[] args) {
Connection conn = null;
String url = "jdbc:mysql://localhost:3306/people";
String jdbcDriver = "com.mysql.jdbc.Driver";
String user = "root";
String password = "hicc";
DbUtils.loadDriver(jdbcDriver);
try {
conn = DriverManager.getConnection(url, user, password);
QueryRunner qr = new QueryRunner();
List results = (List) qr.query(conn, "select id,name from guestmessage", new MapListHandler());
for (int i = 0; i < results.size(); i++) {
Map map = (Map) results.get(i);
System.out.println("id:" + map.get("id") + ",name:" + map.get("name"));
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
DbUtils.closeQuietly(conn);
}
}
}
来源：https://www.cnblogs.com/zhentou/archive/2012/10/20/2691687.html