JDBC学习笔记——利用反射及JDBC元数据编写通用的查询方法

 1 public Customer getCustomer(String sql, Object... args) {
 2         Customer customer = null;
 3         Connection connection = null;
 4         PreparedStatement preparedStatement = null;
 5         ResultSet resultSet = null;
 6         try {
 7             connection = JDBCTools.getConnection();
 8             preparedStatement = connection.prepareStatement(sql);
 9             for (int i = 0; i < args.length; i++) {
10                 preparedStatement.setObject(i + 1, args[i]);
11             }
12             resultSet = preparedStatement.executeQuery();
13             if (resultSet.next()) {
14                 // student = new Student(resultSet.getInt(1),
15                 // resultSet.getInt(2),
16                 // resultSet.getString(3), resultSet.getString(4),
17                 // resultSet.getString(5), resultSet.getString(6),
18                 // resultSet.getInt(7));
19                 customer = new Customer();
20                 customer.setId(resultSet.getInt(1));
21                 customer.setName(resultSet.getString(2));
22                 customer.setEmail(resultSet.getString(3));
23                 customer.setBirth(resultSet.getDate(4));
24             }
25         } catch (Exception e) {
26             e.printStackTrace();
27         } finally {
28             JDBCTools.release(resultSet, preparedStatement, connection);
29         }
30         return customer;
31 
32     }

 1 public Student getStudent(String sql, Object... args) {
 2         Student student = null;
 3         Connection connection = null;
 4         PreparedStatement preparedStatement = null;
 5         ResultSet resultSet = null;
 6         try {
 7             connection = JDBCTools.getConnection();
 8             preparedStatement = connection.prepareStatement(sql);
 9             for (int i = 0; i < args.length; i++) {
10                 preparedStatement.setObject(i + 1, args[i]);
11             }
12             resultSet = preparedStatement.executeQuery();
13             if (resultSet.next()) {
14                 student = new Student(resultSet.getInt(1), resultSet.getInt(2),
15                         resultSet.getString(3), resultSet.getString(4),
16                         resultSet.getString(5), resultSet.getString(6),
17                         resultSet.getInt(7));
18             }
19         } catch (Exception e) {
20             e.printStackTrace();
21         } finally {
22             JDBCTools.release(resultSet, preparedStatement, connection);
23         }
24         return student;
25 
26     }

/**
     * ResultSetMetaData: 
     * 1).是描述ResultSet的元数据对象，即从中可以获取到 结果集中有多少列，列名是什么。。。
     * 2).如何使用呢？ 1.得到ResultSetMetaData对象： 调用ResultSet的getMetaData()方法
     * 2.ResultSetMetaData有哪些好用的方法？
     * 
     * >int getColumnCount():SQL语句中包含哪些列 
     * >String getColumn(int column):获取指定列的别名，其中索引从1开始
     * 
     */

 1 public <T> T get(Class<T> classz, String sql, Object... args) {
 2         T entity = null;
 3         Connection connection = null;
 4         PreparedStatement preparedStatement = null;
 5         ResultSet resultSet = null;
 6         try {
 7             connection = JDBCTools.getConnection();
 8             preparedStatement = connection.prepareStatement(sql);
 9             for (int i = 0; i < args.length; i++) {
10                 preparedStatement.setObject(i + 1, args[i]);
11             }
12             resultSet = preparedStatement.executeQuery();
13 
14             ResultSetMetaData rsmd = resultSet.getMetaData();
15             Map<String, Object> values = new HashMap<String, Object>();
16             if (resultSet.next()) {
17                 for (int i = 0; i < rsmd.getColumnCount(); i++) {
18                     String columnLabel = rsmd.getColumnLabel(i + 1);
19                     Object columnValue = resultSet.getObject(columnLabel);
20                     values.put(columnLabel, columnValue);
21                 }
22             }
23             if (values.size() > 0) {
24                 entity = classz.newInstance();
25                 for (Map.Entry<String, Object> entry : values.entrySet()) {
26                     String fieldName = entry.getKey();
27                     Object fieldValue = entry.getValue();
28                     ReflectionUtils
29                             .setFieldValue(entity, fieldName, fieldValue);
30                 }
31             }
32         } catch (Exception e) {
33             e.printStackTrace();
34         } finally {
35             JDBCTools.release(resultSet, preparedStatement, connection);
36         }
37         // 返回包含查询信息的实体类对象
38         return entity;
39     }

/**
     * 1.先利用SQL进行查询，得到结果集
     * 2.利用反射创建实体类的对象:创建Student对象
     * 3.获取结果集的列的别名：idCard、studentName 
     * 4.再获取结果集的每一列的值，结合3得到一个Map，键是列的别名：值；列的值：{flowid:5,type=6,idCard:xxx...} 列的别名和我们实体类的属性字段名一致
     * 5.再利用反射为2的对应的属性赋值   属性：Map的键   属性值：Map的键值
     */

 1     @Test
 2     public void testGet() {
 3         String sql = "select id,name,email,birth "
 4                 + " from customers where id=?";
 5         System.out.println(sql);
 6         Customer customer = get(Customer.class, sql, 3);
 7         System.out.println(customer);
 8         sql = "select  flow_id flowId,type, idcard idCard, exam_card examCard,"
 9                 + "student_name studentName,location,grade from examstudent where "
10                 + " flow_id=?";
11         System.out.println(sql);
12         Student student = get(Student.class, sql, 3);
13         System.out.println(student);
14     }

select id,name,email,birth  from customers where id=?
Customer [id=3, name=ABCD, email=mike@163.com, birth=1992-06-07]
select  flow_id flowId,type, idcard idCard, exam_card examCard,student_name studentName,location,grade from examstudent where  flow_id=?
Student [flowId=3, type=6, idCard=371522199206078411, examCard=2015534083, studentName=li, location=dalian, grade=87]