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Java内容重新整理删除过期的东西
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Java/JavaDemo/codedemo/dbutils/README.md
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Java/JavaDemo/codedemo/dbutils/README.md
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Apache DbUtils 使用教程
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===
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用JDBC编程时，需要关注和处理的内容非常多，而且很容易造成连接资源没有释放导致泄漏的问题。一个普通的查询操作其处理过程如下：
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1. 创建Connection。
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1. 创建Statement。
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1. 执行SQL生成ResultSet，历遍ResultSet中的所有行记录提取列数据并转换成所需的对象。
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1. 关闭ResultSet。
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1. 关闭Statement。
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1. 关闭Connection。
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`Apache DbUtils`对JDBC操作进行了轻量地封装，解决了两个问题：
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1. 自动创建和释放连接资源，不再有泄漏问题。
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2. 自动将Result转换成对象。填入不同的`ResultSetHandler`，可将ResultSet转换成不同的对象。
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使得代码更加简洁和健壮，让你将精力更多地投入到业务处理中。
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预备
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---
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* MySQL数据库
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* commons-dbutils-1.5.jar
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* mysql-connector-java-5.1.22-bin.jar
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创建表和初始化数据
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---
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1、表结构。
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```sql
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CREATE TABLE `student` (
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`userId` int(11) NOT NULL,
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`userName` varchar(30) NOT NULL,
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`gender` char(1) NOT NULL,
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`age` int(11) DEFAULT NULL,
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PRIMARY KEY (`userId`)
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) ENGINE=InnoDB DEFAULT CHARSET=utf8 ;
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```
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2、初始化数据。
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| userId | userName | gender | age |
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| :--- | :--- | :--- | :--- |
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| 1 | 张三 | M | 20 |
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| 2 | 李四 | M | 21 |
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| 3 | 王五 | M | 22 |
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| 4 | 小明 | M | 6 |
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| 5 | 小丽 | F | 9 |
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编写查询代码
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---
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###1、将查询结果转换成POJO对象列表。
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1）定义一个与表student相对应的对象Student（[源代码下载](https://raw.githubusercontent.com/aofeng/JavaDemo/master/src/cn/aofeng/demo/dbutils/Student.java)）。
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2）使用`BeanListHandler`将查询结果转换成POJO对象列表。
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```java
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public void queryBeanList(DataSource ds) {
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String sql = "select userId, userName, gender, age from student";
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QueryRunner run = new QueryRunner(ds);
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ResultSetHandler<List<Student>> handler = new BeanListHandler<Student>(Student.class);
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List<Student> result = null;
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try {
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result = run.query(sql, handler);
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} catch (SQLException e) {
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_logger.error("获取JDBC连接出错或执行SQL出错", e);
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}
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if (null == result) {
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return;
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}
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for (Student student : result) {
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System.out.println(student);
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}
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}
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```
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执行queryBeanList方法，控制台输出如下信息：
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```
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Student [userId=1, userName=张三, gender=M, age=20]
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Student [userId=2, userName=李四, gender=M, age=21]
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Student [userId=3, userName=王五, gender=M, age=22]
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Student [userId=4, userName=小明, gender=M, age=6]
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Student [userId=5, userName=小丽, gender=F, age=9]
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```
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###2、将查询结果转换成一个POJO象。
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1）定义一个与表student相对应的对象Student（[源代码下载](https://raw.githubusercontent.com/aofeng/JavaDemo/master/src/cn/aofeng/demo/dbutils/Student.java)）。
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2）使用`BeanHandler`将查询结果转换成一个POJO对象。
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```java
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public void queryBean(DataSource ds, int userId) {
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String sql = "select userId, userName, gender, age from student where userId=?";
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QueryRunner run = new QueryRunner(ds);
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ResultSetHandler<Student> handler = new BeanHandler<Student>(Student.class);
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Student result = null;
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try {
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result = run.query(sql, handler, userId);
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} catch (SQLException e) {
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_logger.error("获取JDBC连接出错或执行SQL出错", e);
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}
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System.out.println(result);
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}
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```
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执行queryBean方法，控制台输出如下信息：
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```
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Student [userId=1, userName=张三, gender=M, age=20]
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```
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###3、将查询结果转换成Map对象列表。
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1）使用`MapListHandler`将ResultSet转换成Map对象列表。
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```java
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public void queryMapList(DataSource ds) {
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String sql = "select userId, userName, gender, age from student";
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QueryRunner run = new QueryRunner(ds);
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ResultSetHandler<List<Map<String, Object>>> handler = new MapListHandler();
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List<Map<String, Object>> result = null;
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try {
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result = run.query(sql, handler);
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} catch (SQLException e) {
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_logger.error("获取JDBC连接出错或执行SQL出错", e);
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}
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if (null == result) {
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return;
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}
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for (Map<String, Object> map : result) {
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System.out.println(map);
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}
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}
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```
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执行queryMapList方法，控制台输出如下信息：
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```
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{age=20, userId=1, gender=M, userName=张三}
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{age=21, userId=2, gender=M, userName=李四}
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{age=22, userId=3, gender=M, userName=王五}
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{age=6, userId=4, gender=M, userName=小明}
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{age=9, userId=5, gender=F, userName=小丽}
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```
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###4、将查询结果转换成一个Map对象。
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1）使用`MapHandler`将ResultSet转换成一个Map对象。
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```java
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public void queryMap(DataSource ds, int userId) {
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String sql = "select userId, userName, gender, age from student where userId=?";
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QueryRunner run = new QueryRunner(ds);
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ResultSetHandler<Map<String, Object>> handler = new MapHandler();
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Map<String, Object> result = null;
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try {
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result = run.query(sql, handler, userId);
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} catch (SQLException e) {
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_logger.error("获取JDBC连接出错或执行SQL出错", e);
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}
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System.out.println(result);
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}
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```
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执行queryMap方法，控制台输出如下信息：
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```
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{age=22, userId=3, gender=M, userName=王五}
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```
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###5、自定义ResultSetHandler。
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`Apache DbUtils`自带的各种`ResultSetHandler`已经可以满足绝大部分的查询需求，如果有一些特殊的要求满足不了，可以自己实现一个。
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```java
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public void queryCustomHandler(DataSource ds) {
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String sql = "select userId, userName, gender, age from student";
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// 新实现一个ResultSetHandler
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ResultSetHandler<List<Student>> handler = new ResultSetHandler<List<Student>>() {
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@Override
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public List<Student> handle(ResultSet resultset)
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throws SQLException {
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List<Student> result = new ArrayList<Student>();
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while (resultset.next()) {
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Student student = new Student();
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student.setUserId(resultset.getInt("userId"));
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student.setUserName(resultset.getString("userName"));
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student.setGender(resultset.getString("gender"));
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student.setAge(resultset.getInt("age"));
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result.add(student);
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}
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return result;
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}
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};
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QueryRunner run = new QueryRunner(ds);
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List<Student> result = null;
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try {
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result = run.query(sql, handler);
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} catch (SQLException e) {
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_logger.error("获取JDBC连接出错或执行SQL出错", e);
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}
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if (null == result) {
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return;
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}
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for (Student student : result) {
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System.out.println(student);
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}
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}
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```
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执行queryCustomHandler方法，控制台输出如下信息：
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```
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Student [userId=1, userName=张三, gender=M, age=20]
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Student [userId=2, userName=李四, gender=M, age=21]
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Student [userId=3, userName=王五, gender=M, age=22]
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Student [userId=4, userName=小明, gender=M, age=6]
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Student [userId=5, userName=小丽, gender=F, age=9]
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```
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附录
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---
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* [DEMO完整源代码](https://github.com/aofeng/JavaDemo/edit/master/src/cn/aofeng/demo/dbutils)
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参考资料
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---
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* [commons-dbutils example](http://commons.apache.org/proper/commons-dbutils/examples.html)
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