dbutils使用---QueryRunner(query_update)、BeanList\BeanHandler、MapList\MapHandler、ScalarHandler

1. ResultSetHandler 的作用: QueryRunner 的 query 方法的返回值最终取决于 query 方法的 ResultHandler 参数的 hanlde 方法的返回值.

2. BeanListHandler: 把结果集转为一个 Bean 的 List, 并返回. Bean 的类型在 创建 BeanListHanlder 对象时以 Class 对象的方式传入. 可以适应列的别名来映射 JavaBean 的属性名: String sql = "SELECT id, name customerName, email, birth " + "FROM customers WHERE id = ?"; BeanListHandler(Class<T> type)

3. BeanHandler: 把结果集转为一个 Bean, 并返回. Bean 的类型在创建 BeanHandler 对象时以 Class 对象的方式传入 BeanHandler(Class<T> type)

4. MapHandler: 把结果集转为一个 Map 对象, 并返回. 若结果集中有多条记录, 仅返回 第一条记录对应的 Map 对象. Map 的键: 列名(而非列的别名), 值: 列的值

5. MapListHandler: 把结果集转为一个 Map 对象的集合, 并返回. Map 的键: 列名(而非列的别名), 值: 列的值 6. ScalarHandler: 可以返回指定列的一个值或返回一个统计函数的值.

2、通过QueryRunner实现增删改查

    /**
     * 测试 QueryRunner 的 query 方法
     */
    @SuppressWarnings({ "unchecked", "rawtypes" })
    @Test
    public void testResultSetHandler(){
        String sql = "SELECT id, name, email, birth " +
                "FROM customer";

        //1. 创建 QueryRunner 对象
        QueryRunner queryRunner = new QueryRunner();

        Connection conn = null;

        try {
            conn = JdbcTools.getConnection();
            /**
             * 2. 调用 query 方法:
             * ResultSetHandler 参数的作用: query 方法的返回值直接取决于 
             * ResultSetHandler 的 hanlde(ResultSet rs) 是如何实现的. 实际上, 在
             * QueryRunner 类的 query 方法中也是调用了 ResultSetHandler 的 handle()
             * 方法作为返回值的。
             */
            Object object = queryRunner.query(conn, sql, 
                    new ResultSetHandler(){
                        @Override
                        public Object handle(ResultSet rs) throws SQLException {
                            List<Customer> customers = new ArrayList<>();

                            while(rs.next()){
                                int id = rs.getInt(1);
                                String name = rs.getString(2);
                                String email = rs.getString(3);
                                Date birth = rs.getDate(4);

                                System.out.println(id+","+name+","+email+","+birth);
                                Customer customer = 
                                        new Customer(id, name, email, birth);
                                customers.add(customer);
                            }

                            return customers;
                        }
                    }

                    );          

            System.out.println(object); 
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            JdbcTools.releaseDB(null, null, conn);
        }
    }

log输出日志如下

1,aaa,aaa,2016-10-05
2,bbb,bbb,2016-10-11
[Customer [id=1, name=aaa, email=aaa, birth=2016-10-05], Customer [id=2, name=bbb, email=bbb, birth=2016-10-11]]

删除如下：

    /**
     * 测试 QueryRunner 类的 update 方法
     * 该方法可用于 INSERT, UPDATE 和 DELETE
     */
    @Test
    public void testQueryRunnerUpdate() {
        //1. 创建 QueryRunner 的实现类
        QueryRunner queryRunner = new QueryRunner();

        String sql = "DELETE FROM customer " +
                "WHERE id IN (?,?)";

        Connection connection = null;

        try {
            connection = JdbcTools.getConnection();
            //2. 使用其 update 方法
            int update = queryRunner.update(connection, 
                    sql, 1, 2);
            System.out.println("update:"+update);
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            JdbcTools.releaseDB(null, null, connection);
        }

    }

3、通过BeanListHandler、BeanHandler实现查询操作

/**
     * 测试 ResultSetHandler 的 BeanListHandler 实现类
     * BeanListHandler: 把结果集转为一个 Bean 的 List. 该 Bean
     * 的类型在创建 BeanListHandler 对象时传入:
     * 
     * new BeanListHandler<>(Customer.class)
     * 
     */
    @Test
    public void testBeanListHandler(){
        String sql = "SELECT id, name, email, birth " +
                "FROM customer";

        //1. 创建 QueryRunner 对象
        QueryRunner queryRunner = new QueryRunner();

        Connection conn = null;

        try {
            conn = JdbcTools.getConnection();

            Object object = queryRunner.query(conn, sql, 
                    new BeanListHandler<>(Customer.class)); 
            System.out.println(object);

            ArrayList<Customer> customers = (ArrayList<Customer>) object;
            for (int i = 0; i < customers.size(); i++) {
                Customer customer = customers.get(i);
                System.out.println(customer.getName());
            }


        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            JdbcTools.releaseDB(null, null, conn);
        }
    }

输出如下：

[Customer [id=1, name=aaa, email=aaa, birth=2016-10-05], Customer [id=2, name=bbb, email=bbb, birth=2016-10-11]]
aaa
bbb

•  

    /**
     * BeanHandler: 把结果集的第一条记录转为创建 BeanHandler 对象时传入的 Class 参数对应的对象.
     */

    @Test
    public void testBeanHanlder() {
        QueryRunner queryRunner = new QueryRunner();
        Connection connection = null;

        try {
            connection = JdbcTools.getConnection();
            String sql = "SELECT id, name, email, birth "
                    + "FROM customer WHERE name = ?";

            @SuppressWarnings("unchecked")
            Customer customer = queryRunner.query(connection, sql,
                    new BeanHandler(Customer.class), "bbb");

            System.out.println(customer);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcTools.releaseDB(null, null, null, connection);
        }
    }

输出如下：

Customer [id=2, name=bbb, email=bbb, birth=2016-10-26]