Apache DBUtils使用总结
Apache DBUtils使用总结?DBUtils是个小巧的JDBC轻量级封装的工具包，其最核心的特性是结果集的封装，可以直接将查询出来的结果集封装成JavaBean，这就为我们做了最枯燥乏味、最容易出错的一大部分工作。?在使用DBUtils之前，应该注意一些问题：?1、DBUtils是JDBC的简单封装，可以和JDBC混合使用。?2、DBUtils对结果集自动封装为JavaBean是有着苛刻要求的：必须满足JavaBean的规范，其次Bean的getter与setter方法的名字与结果集的列名一一对应，而不要求JavaBean的私有成员与表结果集列名一一对应。比如：person表中有个字段叫：address，那么对应的JavaBean的Person类中必须有getAddress和setAddress两个方法，而Person类中可以将address属性命名为add，这是没问题的。?3、DBUtils可以将结果集封装为各种类型，主要有：Bean/List<Bean>，Map/List<Map>/Map<Map>，数组/List<数组>，列/List<列>，这些类型。对于Map<Map>的类型使用KeyedHandler作为结果集处理器，内层的Map是“列名-值"对，外层的Map是“主键-内层Map的引用”，但此处的主键不一定就是数据库的主键，可以随意指定，比如：
ResultSetHandler h = new KeyedHandler("id");
Map found = (Map) queryRunner.query("select id, name, age from person", h);
Map jane = (Map) found.get(new Long(1)); // jane's id is 1
String janesName = (String) jane.get("name");
Integer janesAge = (Integer) jane.get("age");?4、DBUtils执行插入操作的时候，无法返回自增主键，这是一个很严重的问题，当然不能怪DBUtils，可以通过变通的方法来实现，比如在MySQL中，执行完了一个插入SQL后，接着执行SELECT LAST_INSERT_ID()语句，就可以获取到自增主键。?5、DBUtils的性能和JDBC性能是一样，测试过程中没发现性能损失，拥有了很高性能的同时，而不失JDBC的灵活性。?6、对于JavaBean的成员类型定义，有一条原则那就是：尽可能使用包装类型，而不要使用基本类型。很多人不理解为什么，包括我见到一些傻B（，我提出让改为包装类型，他还信誓旦旦的说他的代码多牛多叼），都干好多年了，这个简单的道理还不知道:??????? //错误
??????? int a1 = (Integer) null;
??????? boolean x1 = (Boolean)null;
??????? //正确
??????? Integer a2 = (Integer) null;
??????? Boolean x2 = (Boolean)null;?实际上就是为了保证在查询结果为null的时候，也不会因为给基本类型赋null值而发生错误。?下面给出一个简单例子，作为以后写代码时候有点参考：?环境：MySQL5.4JDK1.5?建表SQL：CREATE TABLE person (
???? id bigint(20) NOT NULL AUTO_INCREMENT,
???? name varchar(24) DEFAULT NULL,
???? age int(11) DEFAULT NULL,
???? address varchar(120) DEFAULT NULL,
???? PRIMARY KEY (id)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=gbk?Java代码：public class Person {
????????private Long id;
????????private String sdf;
????????private String address2;
????????private Integer age;
????????public Person() {
????????}
????????public Person(String sdf) {
????????????????this.sdf = sdf;
????????}
????????public Person(String sdf, Integer age, String address) {
????????????????this.sdf = sdf;
????????????????this.age = age;
????????????????this.address2 = address;
????????}
????????public Long getId() {
????????????????return id;
????????}
????????public void setId(Long id) {
????????????????this.id = id;
????????}
????????public String getSdf() {
????????????????return sdf;
????????}
????????public void setSdf(String sdf) {
????????????????this.sdf = sdf;
????????}
????????public Integer getAge() {
????????????????return age;
????????}
????????public void setAge(Integer age) {
????????????????this.age = age;
????????}
????????public String getAddress() {
????????????????return address2;
????????}
????????public void setAddress(String address2) {
????????????????this.address2 = address2;
????????}
}?测试package com.lavasoft.dbstu;
import com.lavasoft.common.DBToolkit;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.MapHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;
/**
* Created by IntelliJ IDEA.
*
* @author leizhimin 2010-1-25 21:00:29
*/
public class PersonDAOImpl implements PersonDAO {
????????private static PersonDAOImpl instance = new PersonDAOImpl();
????????public static PersonDAOImpl getInstance() {
????????????????return instance;
????????}
????????public static void main(String[] args) {
????????????????//错误
????????????????int a1 = (Integer) null;
????????????????boolean x1 = (Boolean) null;
????????????????//正确
????????????????Integer a2 = (Integer) null;
????????????????Boolean x2 = (Boolean) null;
????????????????getInstance().save(null);
//????????????????getInstance().save(null);
//????????????????getInstance().save(null);
//????????????????getInstance().save(null);
//????????????????getInstance().save(null);
????????????????getInstance().update(null);
????????????????getInstance().load(null);
????????????????getInstance().load4Map(null);
????????}
????????@Override
????????public Long save(String sql) {
????????????????Long id = null;
????????????????String ins_sql = "INSERT INTO person (NAME, age, address) VALUES ('aaa', 21, 'address001')";
????????????????Connection conn = DBToolkit.getConnection();
????????????????QueryRunner qr = new QueryRunner();
????????????????try {
????????????????????????qr.update(conn, ins_sql);
????????????????????????//获取新增记录的自增主键
????????????????????????id = (Long) qr.query(conn, "SELECT LAST_INSERT_ID()", new ScalarHandler(1));
????????????????} catch (SQLException e) {
????????????????????????e.printStackTrace();
????????????????} finally {
????????????????????????DBToolkit.closeConnection(conn);
????????????????}
????????????????return id;
????????}
????????@Override
????????public int delete(Long id) {
????????????????int x = 0;
????????????????Connection conn = DBToolkit.getConnection();
????????????????QueryRunner qr = new QueryRunner();
????????????????try {
????????????????????????x = qr.update(conn, "DELETE FROM person WHERE id = ?", id);
????????????????} catch (SQLException e) {
????????????????????????e.printStackTrace();
????????????????} finally {
????????????????????????DBToolkit.closeConnection(conn);
????????????????}
????????????????return x;
????????}
????????@Override
????????public int update(Person person) {
????????????????int x = 0;
????????????????Connection conn = DBToolkit.getConnection();
????????????????QueryRunner qr = new QueryRunner();
????????????????try {
????????????????????????x = qr.update(conn, "UPDATE person SET NAME = ?, age = ?, address = ? WHERE id = ?", "xxx", 23, "ttt", 5);
????????????????} catch (SQLException e) {
????????????????????????e.printStackTrace();
????????????????} finally {
????????????????????????DBToolkit.closeConnection(conn);
????????????????}
????????????????return x;
????????}
????????@Override
????????public Person load(Long id) {
????????????????Connection conn = DBToolkit.getConnection();
????????????????QueryRunner qr = new QueryRunner();
????????????????try {
????????????????????????Person person = (Person) qr.query(conn, "SELECT * FROM person where id = ?", new BeanHandler(Person.class), 3L);
????????????????????????System.out.println(person.getId() + "\t" + person.getSdf() + "\t" + person.getAge() + "\t" + person.getAddress());
????????????????} catch (SQLException e) {
????????????????????????e.printStackTrace();
????????????????}
????????????????return null;
????????}
????????@Override
????????public List<Person> findPerson(String sql) {
????????????????Connection conn = DBToolkit.getConnection();
????????????????QueryRunner qr = new QueryRunner();
????????????????try {
????????????????????????List<Person> pset = (List) qr.query(conn, "SELECT * FROM person", new BeanListHandler(Person.class));
????????????????????????for (Person person : pset) {
????????????????????????????????System.out.println(person.getId() + "\t" + person.getSdf() + "\t" + person.getAge() + "\t" + person.getAddress());
????????????????????????}
????????????????} catch (SQLException e) {
????????????????????????e.printStackTrace();
????????????????}
????????????????return null;
????????}
????????public Person load4Map(Long id) {
????????????????Connection conn = DBToolkit.getConnection();
????????????????QueryRunner qr = new QueryRunner();
????????????????try {
????????????????????????//先将两个字段置为null
????????????????????????qr.update(conn, "update person set age = null,address =null where id =1");
????????????????????????Map<String, Object> map = qr.query(conn, "SELECT * FROM person where id = ?", new MapHandler(), 1L);
????????????????????????Person person = new Person();
????????????????????????person.setId((Long) map.get("id"));
????????????????????????person.setSdf((String) map.get("name"));
????????????????????????person.setAge((Integer) map.get("age"));
????????????????????????person.setAddress((String) map.get("address"));
????????????????????????System.out.println(person.getId() + "\t" + person.getSdf() + "\t" + person.getAge() + "\t" + person.getAddress());
????????????????} catch (SQLException e) {
????????????????????????e.printStackTrace();
????????????????}
????????????????return null;
????????}
}?注意：从上面的过程看，每个SQL的执行都需要用到QueryRunner，这其实是一个普通的类，非线程安全。在创建这个QueryRunner对象的时候，每次都要new。?QueryRunner对象的创建方式很多，可以通过DateSource，也可以通过Connection来创建。从QueryRunner对象上，可以直接获取到DataSource或者Connection对象。
转自：http://lavasoft.blog.51cto.com/62575/270661