JDBC连接Mysql数据库 (使用Java反射进行优化)

古城微笑少年丶 2021-12-24 07:49 289阅读 0赞

**一、下载mysql驱动**

** **  下载mysql驱动教程链接：[https://jingyan.baidu.com/article/c275f6ba6bf785e33d756707.html][https_jingyan.baidu.com_article_c275f6ba6bf785e33d756707.html]

**二、把下载好的mysql驱动复制粘贴到项目的lib文件夹下 (如果没有lib文件夹，就在项目下新建一个lib文件夹)，然后选中mysql驱动包鼠标右键选择 Build Path → Add to Build Path**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5MTM1Mjg3_size_16_color_FFFFFF_t_70][]

**三、优化 JDBC连接Mysql数据库的 增加、删除和修改方法**

**3.1、首先让我们来看一下优化前的添加、修改和删除方法 有什么缺点**

3.1.1、创建一个Student实体类，用于JDBC连接Mysql数据库

package com.mysql.pojo;
    
    public class Student implements Serializable{
    
    	private Integer id;
    	private String name;
    	private String sex;
    	
    
    	public Student() {}
    
    	public Integer getId() {
    		return id;
    	}
    
    	public void setId(Integer id) {
    		this.id = id;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	public String getSex() {
    		return sex;
    	}
    
    	public void setSex(String sex) {
    		this.sex = sex;
    	}
    
    	public String toString() {
    		return "Student [id=" + id + ", name=" + name + ", sex=" + sex + "]";
    	}
    	
    }

3.1.2、添加数据方法

public void add(Student student) {
    		Connection conn = null;
    		PreparedStatement stmt = null;
    		
    		try {
    			
    			// 1、注册驱动 
    			Class.forName("com.mysql.jdbc.Driver");
    			
    			String url = "jdbc:mysql://localhost:3306/mytest";  //连接数据库的url 格式：协议 ://主机名:端口号/数据库名称
    			String user = "root"; //mysql数据库账号
    			String password = "123456"; //mysql数据库密码
    			
    			//2、获取与mysql数据库的连接 Connection
    			conn = DriverManager.getConnection(url, user, password);
    			//3、编写mysql语句
    			String sql = "insert into student(id,name,sex) values(?,?,?)";
    			stmt = conn.prepareStatement(sql);
    			//4、替换mysql语句中的问号 (注意：下标是从1开始的)
    			stmt.setObject(1, student.getId());
    			stmt.setObject(2, student.getName());
    			stmt.setObject(3, student.getSex());
    		
    			//5、执行executeUpdate
    			int executeUpdate = stmt.executeUpdate();
    
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		} finally {
    			
    			//6、释放资源
    			if (stmt != null) {
    				try {
    					stmt.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				stmt = null;
    			}
    
    			if (conn != null) {
    				try {
    					conn.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    				
    				conn = null;
    			}
    		}
    
    	}

3.1.3、修改数据方法

public void update(Student student) {
    		Connection conn = null;
    		PreparedStatement stmt = null;
    
    		try {
    
    			// 1、注册驱动
    			Class.forName("com.mysql.jdbc.Driver");
    
    			String url = "jdbc:mysql://localhost:3306/mytest"; // 连接数据库的url 格式：协议 ://主机名:端口号/数据库名称
    			String user = "root"; // mysql数据库账号
    			String password = "123456"; // mysql数据库密码
    
    			// 2、获取与mysql数据库的连接 Connection
    			conn = DriverManager.getConnection(url, user, password);
    			// 3、编写mysql语句
    			String sql = "update student set name=?, sex=? where id=?";
    			stmt = conn.prepareStatement(sql);
    			// 4、替换mysql语句中的问号 (注意：下标是从1开始的)
    			stmt.setObject(1, student.getName());
    			stmt.setObject(2, student.getSex());
    			stmt.setObject(3, student.getId());
    
    			// 5、执行executeUpdate
    			int executeUpdate = stmt.executeUpdate();
    
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		} finally {
    
    			// 6、释放资源
    			if (stmt != null) {
    				try {
    					stmt.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				stmt = null;
    			}
    
    			if (conn != null) {
    				try {
    					conn.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				conn = null;
    			}
    		}
    
    	}

3.1.4、删除数据方法

public void delete(Integer id) {
    		Connection conn = null;
    		PreparedStatement stmt = null;
    
    		try {
    
    			// 1、注册驱动
    			Class.forName("com.mysql.jdbc.Driver");
    
    			String url = "jdbc:mysql://localhost:3306/mytest"; // 连接数据库的url 格式：协议 ://主机名:端口号/数据库名称
    			String user = "root"; // mysql数据库账号
    			String password = "123456"; // mysql数据库密码
    
    			// 2、获取与mysql数据库的连接 Connection
    			conn = DriverManager.getConnection(url, user, password);
    			// 3、编写mysql语句
    			String sql = "delete from student where id=?";
    			stmt = conn.prepareStatement(sql);
    			// 4、替换mysql语句中的问号 (注意：下标是从1开始的)
    			stmt.setObject(1, id);
    			
    			// 5、执行executeUpdate
    			int executeUpdate = stmt.executeUpdate();
    			
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		} finally {
    
    			// 6、释放资源
    			if (stmt != null) {
    				try {
    					stmt.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				stmt = null;
    			}
    
    			if (conn != null) {
    				try {
    					conn.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				conn = null;
    			}
    		}
    
    	}

**3.2、通过对比发现，添加、修改和删除方法，除了方法参数、mysql数据库语句和替换mysql语句中的问号不同，其他步骤都是相同的，这时我们可以对这三个方法进行提取和优化，使其变成一个方法，其优化之后的结果如下：**

3.2.1、创建一个jdbc.properties文件，在文件中添加如下信息：

driver=com.mysql.jdbc.Driver
    url=jdbc:mysql://localhost:3306/mytest
    name=root
    password=123456

3.2.2、优化之后的MysqlDemo类

package com.mysql.demo;
    
    import java.io.InputStream;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.util.Properties;
    
    public class MysqlDemo {
    
    	private static Properties properties = null;
    	private static Connection connection = null;
    	private static PreparedStatement statement = null;
    	private static ResultSet resultSet = null;
    
    	static {
    
    		try {
    			// 1.注册驱动
    			InputStream resourceAsStream = MysqlDemo.class.getClassLoader().getResourceAsStream("jdbc.properties");
    			properties = new Properties();
    			properties.load(resourceAsStream);
    			String property = properties.getProperty("className");
    
    			Class.forName(property);
    
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    	// 获取与mysql数据库的连接
    	public static Connection getConnection() {
    		try {
    			// 2.获取连接
    			String url = properties.getProperty("url");
    			String user = properties.getProperty("user");
    			String password = properties.getProperty("password");
    			return DriverManager.getConnection(url, user, password);
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		}
    	}
    
            /*
             * 添加、修改和删除方法优化 
             * 返回值为Integer:影响行数
             * 参数: 
             *   sql:Mysql数据库查询语句 
             *   array:可变参数
             */
    	public static Integer Update(String sql, Object... array) {
    		try {
    			connection = MysqlDemo.getConnection();
    			statement = connection.prepareStatement(sql);
    			for (int i = 0; i < array.length; i++) {
    				statement.setObject(i + 1, array[i]);
    			}
    			return statement.executeUpdate();
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		} finally {
    
    			closeAll(null, statement, connection);
    		}
    	}
    
    	// 关闭资源
    	public static void closeAll(ResultSet resultSet, PreparedStatement statement, Connection connection) {
    		// 关闭resultSet
    		if (resultSet != null) {
    			try {
    				resultSet.close();
    			} catch (Exception e) {
    				throw new RuntimeException(e);
    			} finally {
    				resultSet = null;
    			}
    
    		}
    
    		// 关闭statement
    		if (statement != null) {
    			try {
    				statement.close();
    			} catch (Exception e) {
    				throw new RuntimeException(e);
    			} finally {
    				statement = null;
    			}
    
    		}
    
    		// 关闭connection
    		if (connection != null) {
    			try {
    				connection.close();
    			} catch (Exception e) {
    				throw new RuntimeException(e);
    			} finally {
    				connection = null;
    			}
    
    		}
    
    	}
    
    }

3.2.3、使用方式如下：

public static void main(String[] args) {
    
    		Student student = new Student();
    		student.setId(1);
    		student.setName("李四");
    		student.setSex("男");
    
    		// ------------添加数据操作------------
    		String addSql = "insert into student(id,name,sex) values(?,?,?)";
    		MysqlDemo.Update(addSql, student.getId(), student.getName(), student.getSex());
    
    		// ------------修改数据操作------------
    		student.setName("王五");
    		student.setSex("女");
    		String updateSql = "update student set name=?, sex=? where id=?";
    		MysqlDemo.Update(updateSql, student.getId(), student.getName(), student.getSex());
    
    		// ------------删除数据操作------------
    		String deleteSql = "delete from student  where id=?";
    		MysqlDemo.Update(updateSql, student.getId());
    }

**四、优化 JDBC连接Mysql数据库的 查询方法**

**   4.1、由于查询比较复杂，查询的返回结果可以是一个对象、一个对象集合、一个字段集合或者一个字段(例如查询count(\*) )，首先让我们来看一下优化前的查询方法，有什么缺点**

4.1.1、查询数据方法，并返回一个对象

public Student select(Integer id) {
    		Connection conn = null;
    		PreparedStatement stmt = null;
    		ResultSet resultSet = null;
    
    		try {
    
    			// 1、注册驱动
    			Class.forName("com.mysql.jdbc.Driver");
    
    			String url = "jdbc:mysql://localhost:3306/mytest"; // 连接数据库的url 格式：协议 ://主机名:端口号/数据库名称
    			String user = "root"; // mysql数据库账号
    			String password = "123456"; // mysql数据库密码
    
    			// 2、获取与mysql数据库的连接 Connection
    			conn = DriverManager.getConnection(url, user, password);
    			// 3、编写mysql语句
    			String sql = "select * from student where id=?";
    			stmt = conn.prepareStatement(sql);
    			// 4、替换mysql语句中的问号 (注意：下标是从1开始的)
    			stmt.setObject(1, id);
    			// 5、执行executeQuery
    			resultSet = stmt.executeQuery();
    
    			// 6、创建Student实体类对象
    			Student student = new Student();
    
    			if (resultSet.next()) {
    				student.setId(resultSet.getInt("id"));
    				student.setName(resultSet.getString("name"));
    				student.setSex(resultSet.getString("sex"));
    			}
    
    			return student;
    
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		} finally {
    
    			// 6、释放资源
    			if (stmt != null) {
    				try {
    					stmt.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				stmt = null;
    			}
    
    			if (conn != null) {
    				try {
    					conn.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				conn = null;
    			}
    
    			if (resultSet != null) {
    				try {
    					resultSet.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				resultSet = null;
    			}
    		}
    
    	}

4.1.2、查询数据方法，并返回一个对象的集合

public List<Student> select(String sex) {
    		Connection conn = null;
    		PreparedStatement stmt = null;
    		ResultSet resultSet = null;
    
    		try {
    
    			// 1、注册驱动
    			Class.forName("com.mysql.jdbc.Driver");
    
    			String url = "jdbc:mysql://localhost:3306/mytest"; // 连接数据库的url 格式：协议 ://主机名:端口号/数据库名称
    			String user = "root"; // mysql数据库账号
    			String password = "123456"; // mysql数据库密码
    
    			// 2、获取与mysql数据库的连接 Connection
    			conn = DriverManager.getConnection(url, user, password);
    			// 3、编写mysql语句
    			String sql = "select * from student where sex=?";
    			stmt = conn.prepareStatement(sql);
    			// 4、替换mysql语句中的问号 (注意：下标是从1开始的)
    			stmt.setObject(1, sex);
    			// 5、执行executeQuery
    			resultSet = stmt.executeQuery();
    
    			// 6、声明Student实体类对象
    			Student student = null;
               
    			//7、创建对象集合
    			ArrayList<Student> list = new ArrayList<>();
    			
    			while (resultSet.next()) {
    				student = new Student();
    				student.setId(resultSet.getInt("id"));
    				student.setName(resultSet.getString("name"));
    				student.setSex(resultSet.getString("sex"));
    				
    				//8、添加到对象集合中
    				list.add(student);
    			}
    
    			return list;
    
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		} finally {
    
    			// 9、释放资源
    			if (stmt != null) {
    				try {
    					stmt.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				stmt = null;
    			}
    
    			if (conn != null) {
    				try {
    					conn.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				conn = null;
    			}
    
    			if (resultSet != null) {
    				try {
    					resultSet.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				resultSet = null;
    			}
    		}
    
    	}

4.1.3、查询数据方法，并返回一个字段集合

public List<String> select() {
    		Connection conn = null;
    		PreparedStatement stmt = null;
    		ResultSet resultSet = null;
    
    		try {
    
    			// 1、注册驱动
    			Class.forName("com.mysql.jdbc.Driver");
    
    			String url = "jdbc:mysql://localhost:3306/mytest"; // 连接数据库的url 格式：协议 ://主机名:端口号/数据库名称
    			String user = "root"; // mysql数据库账号
    			String password = "123456"; // mysql数据库密码
    
    			// 2、获取与mysql数据库的连接 Connection
    			conn = DriverManager.getConnection(url, user, password);
    			// 3、编写mysql语句
    			String sql = "select name from student";
    			stmt = conn.prepareStatement(sql);
    
    			// 4、执行executeQuery
    			resultSet = stmt.executeQuery();
    
    			// 5、创建String数据类型集合
    			ArrayList<String> list = new ArrayList<>();
    
    			while (resultSet.next()) {
    				String num = resultSet.getString("name");
    				// 6、添加到String数据类型集合中
    				list.add(num);
    			}
    
    			return list;
    
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		} finally {
    
    			// 6、释放资源
    			if (stmt != null) {
    				try {
    					stmt.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				stmt = null;
    			}
    
    			if (conn != null) {
    				try {
    					conn.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				conn = null;
    			}
    
    			if (resultSet != null) {
    				try {
    					resultSet.close();
    				} catch (SQLException sqlex) {
    					throw new RuntimeException(sqlex);
    				}
    
    				resultSet = null;
    			}
    		}
    
    	}

4**.2、通过对比发现，查询的三个方法，除了方法参数、mysql数据库语句、替换mysql语句中的问号、resultSet结果集处理和返回值不同，其他步骤都是相同的，这时我们可以对这三个方法进行提取和优化，使其变成一个方法，其优化之后的结果如下：**

4.2.1、创建一个jdbc.properties文件，在文件中添加如下信息：

driver=com.mysql.jdbc.Driver
    url=jdbc:mysql://localhost:3306/mytest
    name=root
    password=123456

4.2.2、优化之后的MysqlDemo类

package com.mysql.demo;
    
    import java.io.InputStream;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.util.Properties;
    
    import com.mysql.dbutil.ResultSetHandler;
    
    public class MysqlDemo {
    
    	private static Properties properties = null;
    	private static Connection connection = null;
    	private static PreparedStatement statement = null;
    	private static ResultSet resultSet = null;
    
    	static {
    
    		try {
    			// 1.注册驱动
    			InputStream resourceAsStream = MysqlDemo.class.getClassLoader().getResourceAsStream("jdbc.properties");
    			properties = new Properties();
    			properties.load(resourceAsStream);
    			String property = properties.getProperty("className");
    
    			Class.forName(property);
    
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    	// 获取与mysql数据库的连接
    	public static Connection getConnection() {
    		try {
    			// 2.获取连接
    			String url = properties.getProperty("url");
    			String user = properties.getProperty("user");
    			String password = properties.getProperty("password");
    			return DriverManager.getConnection(url, user, password);
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		}
    	}
    
    
           /*
            * 查询方法优化 返回值使用Object,来解决返回值不同的问题
            * 参数: 
            *   sql:Mysql数据库查询语句 
            *   handler:resultSet结果集处理接口
            *   array:可变参数
            */
    	public static Object Query(String sql, ResultSetHandler handler, Object... array) {
    
    		try {
    			connection = MysqlDemo.getConnection();
    			statement = connection.prepareStatement(sql);
    			for (int i = 0; i < array.length; i++) {
    				statement.setObject(i + 1, array[i]);
    			}
    			resultSet = statement.executeQuery();
    			return handler.Handler(resultSet);
    
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		} finally {
    			closeAll(resultSet, statement, connection);
    		}
    
    	}
    
    	// 关闭资源
    	public static void closeAll(ResultSet resultSet, PreparedStatement statement, Connection connection) {
    		// 关闭resultSet
    		if (resultSet != null) {
    			try {
    				resultSet.close();
    			} catch (Exception e) {
    				throw new RuntimeException(e);
    			} finally {
    				resultSet = null;
    			}
    
    		}
    
    		// 关闭statement
    		if (statement != null) {
    			try {
    				statement.close();
    			} catch (Exception e) {
    				throw new RuntimeException(e);
    			} finally {
    				statement = null;
    			}
    
    		}
    
    		// 关闭connection
    		if (connection != null) {
    			try {
    				connection.close();
    			} catch (Exception e) {
    				throw new RuntimeException(e);
    			} finally {
    				connection = null;
    			}
    
    		}
    
    	}
    }

4.2.3、resultSet结果集处理接口类

package com.mysql.dbutil;
    
    import java.sql.ResultSet;
    
    public interface ResultSetHandler {
    
    	// 处理resultSet结果集抽象方法
    	public abstract Object Handler(ResultSet resultSet);
    
    }

4.2.4、处理对象的ResultSetHandler接口实现类 --- BeanResultSetHandler

package com.mysql.dbutil;
    
    import java.lang.reflect.Field;
    import java.sql.ResultSet;
    import java.sql.ResultSetMetaData;
    
    public class BeanResultSetHandler implements ResultSetHandler {
    
    	//字节码文件对象字段
    	public Class<?> clazz;
    
    	public BeanResultSetHandler(Class<?> clazz) {
    		this.clazz = clazz;
    	}
    
    	public Object Handler(ResultSet resultSet) {
    		try {
    			//通过反射创建实体类对象
    			Object object = clazz.newInstance();
    			
    			//获取此 ResultSet 对象的列的编号、类型和属性。
    			ResultSetMetaData metaData = (ResultSetMetaData) resultSet.getMetaData();
    			
    			//获取此 ResultSet 对象中的列数
    			int Columncount = metaData.getColumnCount();
    			if (resultSet.next()) {
    				for (int i = 0; i < Columncount; i++) {
    					//获取指定列的名称
    					String name = metaData.getColumnName(i + 1);
    
    					//通过反射获取字段
    					Field field = clazz.getDeclaredField(name);
    					field.setAccessible(true);
    					//设置字段值
    					field.set(object, resultSet.getObject(name));
    				}
    			}
    
    			return object;
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		}
    	}
    }

4.2.5、处理集合的ResultSetHandler接口实现类 --- ListResultSetHandler

package com.mysql.dbutil;
    
    import java.lang.reflect.Field;
    import java.sql.ResultSet;
    import java.sql.ResultSetMetaData;
    import java.util.ArrayList;
    import java.util.List;
    
    public class ListResultSetHandler implements ResultSetHandler {
    
    	// 字节码文件对象字段
    	public Class<?> clazz;
    
    	public ListResultSetHandler(Class<?> clazz) {
    		this.clazz = clazz;
    	}
    
    	public Object Handler(ResultSet resultSet) {
    
    		try {
    			List<Object> list = new ArrayList<Object>();
    
    			// 获取此 ResultSet 对象的列的编号、类型和属性。
    			ResultSetMetaData metaData = (ResultSetMetaData) resultSet.getMetaData();
    
    			// 获取此 ResultSet 对象中的列数
    			int Columncount = metaData.getColumnCount();
    			Object object = null;
    
    			while (resultSet.next()) {
    				// 通过反射创建实体类对象
    				object = clazz.newInstance();
    
    				for (int i = 0; i < Columncount; i++) {
    					// 获取指定列的名称
    					String name = metaData.getColumnName(i + 1);
    
    					// 通过反射获取字段
    					Field field = clazz.getDeclaredField(name);
    					field.setAccessible(true);
    					// 设置字段值
    					field.set(object, resultSet.getObject(i + 1));
    				}
    
    				list.add(object);
    			}
    
    			return list;
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		}
    	}
    }

4.2.6、处理字段集合的ResultSetHandler接口实现类 --- ColumnResultSetHandler

package com.mysql.dbutil;
    
    import java.sql.ResultSet;
    import java.util.ArrayList;
    import java.util.List;
    
    public class ColumnResultSetHandler implements ResultSetHandler {
    
    	// 要查询的字段
    	public String str;
    
    	public ColumnResultSetHandler(String str) {
    		this.str = str;
    	}
    
    	public Object Handler(ResultSet resultSet) {
    		try {
    			List<Object> list = new ArrayList<Object>();
    			while (resultSet.next()) {
    				Object object = resultSet.getObject(str);
    				list.add(object);
    			}
    			return list;
    		} catch (Exception e) {
    			throw new RuntimeException(e);
    		}
    	}
    }

4.2.7、使用方式如下：

public static void main(String[] args) {
    
    		// ------------查询数据，并返回一个对象集合------------
    		String sqlForBean = "select * from student where id=?";
    		ResultSetHandler handlerForBean = new BeanResultSetHandler(Student.class);
    		Student student = (Student) MysqlDemo.Query(sqlForBean, handlerForBean, 1);
    
    		// ------------查询数据，并返回一个对象集合------------
    		String sqlForList = "select * from student where sex=?";
    		ResultSetHandler handlerForList = new ListResultSetHandler(Student.class);
    		List<Student> list = (List<Student>) MysqlDemo.Query(sqlForList, handlerForList, "男");
    
    		// ------------查询数据，并返回一个字段集合------------
    		String sqlForColumn = "select name from student where sex=?";
    		ResultSetHandler handlerForColumn = new ColumnResultSetHandler("name");
    		List<String> listForColumn = (List<String>) MysqlDemo.Query(sqlForColumn, handlerForColumn, "男");
    
    		// ------------查询数据，并返回一个字段------------
    		String sqlForField = "select count(*) from student";
    		ResultSetHandler handlerForField = new ColumnResultSetHandler("count(*)");
    		List<Integer> listForField = (List<Integer>) MysqlDemo.Query(sqlForField, handlerForField);
    		Integer count = listForField.get(0);
    
    	}

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