java学习之路—JDBC—DBUtils

1.需要导的包

commons-dbutils-jar

2.用处

利用dbutils提供的方法 便捷的访问数据库 更新 查询

3.主要方法

    QueryRunner的quer方法的返回值取决于其ResultSetHandler参数的handle方法的返回值

    QueryRunner queryRunner = new QueryRunner();

public void testQuery() {
Connection connection = null;

try {
connection = JDBCTools.getConnection();
String sql = "SELECT id,name,email,birth FROM customers";
Object obj = queryRunner.query(connection, sql, new MyResultSetHandler());
System.out.println(obj);
} catch (Exception e) {
e.printStackTrace();
} finally {
JDBCTools.releaseRs(null, connection, null);
}

}

   1.BeanHandler:把结果集的第一条记录转为创建的BeanHandler 对象时传入 的class参数对应的对象

       public void testBeanHanlder() {

Connection connection = null;
try {
connection = JDBCTools.getConnection();
String sql = "SELECT id,name,email,birth FROM customers WHERE id = ?";
Customer customer = queryRunner.query(connection, sql, new BeanHandler<>(Customer.class), 5);

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

2. BeanListHandler:把结果集转为一个List，该List不为null； 但可能为空集合（size（） 方法返回 0 ）

 public void testBeanListHandler() {
           Connection connection = null;
              try {
connection = JDBCTools.getConnection();
String sql = "SELECT id,name,email,birth FROM customers ";
List<Customer> customers = queryRunner.query(connection, sql, new BeanListHandler<>(Customer.class));

System.out.println(customers);
} catch (Exception e) {
e.printStackTrace();
} finally {
JDBCTools.releaseRs(null, connection, null);
}

}

3.MapHandler

public void testMapHandler() {
Connection connection = null;
try {
connection = JDBCTools.getConnection();
String sql = "SELECT id,name,email,birth FROM customers";
Map<String, Object> customer = queryRunner.query(connection, sql, new MapHandler());

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

4.MapListHandler:将结果集转为一个Map的List   Map对应查询的一条记录

public void TestMapListHandler() {
Connection connection = null;
try {
connection = JDBCTools.getConnection();
String sql = "SELECT id,name,email,birth FROM customers";
List<Map<String, Object>> customer = queryRunner.query(connection, sql, new MapListHandler());

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

}

5.Scarlar把结果集转为一个数值返回（可以是任意类型的 字符  数字）

public void testScalarHandler() {
Connection connection = null;
try {
connection = JDBCTools.getConnection();
String sql = "SELECT name FROM customers WHERE id = ?";
String result = queryRunner.query(connection, sql, new ScalarHandler<>(),5);

System.out.println(result);
} catch (Exception e) {
e.printStackTrace();
} finally {
JDBCTools.releaseRs(null, connection, null);
}

}