关于java:简单实现DbUtil的query与update方法

写在后面

在浏览本文之前，你或者应该先理解：

• JDBC的实现步骤(注册驱动、建设连贯、发送SQL、处理结果集)
• 数据库连接池的应用(本文应用c3p0连接池)

DbUtils是Apache的一个对于数据库操作的封装类，本文重写了DbUtils的query与update办法,而代码着重于封装的实现原理,对于很多异样等都未做具体的解决。

实现步骤

1. 首先,通过c3p0连接池建设数据库连贯,并获取连贯对象。

• 导入c3p0-0.9.2-pre1.jar
• 创立c3p0.properties或c3p0-config.xml文件,上面是.xml文件次要内容:

<?xml version="1.0" encoding="UTF-8"?>  
<c3p0-config>  
 <!-- 默认配置，当应用ComboPooledDataSource无参结构器时，应用的就是这个配置 -->  
 <default-config>  
 <!-- 根本配置 -->  
 <property name="jdbcUrl">jdbc:mysql://127.0.0.1:3306/share?serverTimezone=Asia/Shanghai&amp;useSSL=false&amp;characterEncoding=utf8</property>  
 <property name="driverClass">com.mysql.cj.jdbc.Driver</property>  
 <property name="user">root</property>  
 <property name="password">123456</property>  
 <!-- 每次增量，当须要创立Connection对象时，一次创立几个 -->  
 <property name="acquireIncrement">3</property>  
 <!-- 当创立池对象后，池中应该有几个Connection对象 -->  
 <property name="initialPoolSize">10</property>  
 <!-- 池中起码Connection个数，如果少于这个值，就会创立Connection -->  
 <property name="minPoolSize">2</property>  
 <!-- 池中最大连贯个数 -->  
 <property name="maxPoolSize">15</property>  
 </default-config>
</c3p0-config> 

• 创立数据库连接池，获取连贯对象的包装类JdbcUtil

public class JdbcUtil {  
    private static ComboPooledDataSource dataSource = new ComboPooledDataSource();  
  
 public static Connection getConnection(){  
        Connection conn = null;  
 try {  
            conn = dataSource.getConnection();  
 } catch (SQLException e) {  
            e.printStackTrace();  
 }  
        return conn;  
 }  
  
    public static DataSource getDataSource(){  
        return dataSource;  
 }  
}

1. 数据库增删查改的类MyRunner

public class MyRunner {  
    private DataSource dataSource;  
  
 public MyRunner(DataSource dataSource){  
        this.dataSource = dataSource;  
 }  
  
    public <T> T query(String sql, MyResultSetHandler<T> handler, Object... params){  
        T result = null;  
 try {  
            Connection conn = dataSource.getConnection();  
 PreparedStatement pstmt = conn.prepareStatement(sql);  
 generateParams(pstmt, params); // 给pstmt赋值  
 result = handler.handle(pstmt.executeQuery());  
 } catch (SQLException e) {  
            e.printStackTrace();  
 }  
        return result;  
 }  
  
    /**  
 * 数据操作 包含增、删、改  
 * @param sql sql语句  
 * @param params 参数列表  
 */  
 public void update(String sql, Object... params){  
        try {  
            Connection conn = dataSource.getConnection();  
 PreparedStatement pstmt = conn.prepareStatement(sql);  
 generateParams(pstmt, params); // 给pstmt赋值  
 pstmt.executeUpdate();  
 } catch (SQLException e) {  
            e.printStackTrace();  
 }  
    }  
  
    /**  
 * 给指定的pstmt 预处理的? 赋值  
 * @param pstmt PreparedStatement  
 * @param params 参数列表  
 * @throws SQLException  
 */ private static void generateParams(PreparedStatement pstmt, Object[] params) throws SQLException {  
        for(int i = 1; i <= params.length; i++){  
            pstmt.setObject(i, params[i-1]);  
 }  
    }  
}

1. 创立对立的解决ResultSet后果集的接口类MyResultSetHandler

/**  
 * @Auther dbc  
 * @Date 2020/9/11 17:04  
 */
public interface MyResultSetHandler<T> {  
    T handle(ResultSet resultSet) throws SQLException;  
}

1. 实现上一步的接口MyBeanHandler

public class MyBeanHandler<T> implements MyResultSetHandler<T> {  
  
    private Class<T> clazz;  
  
 public MyBeanHandler(Class<T> T){  
        this.clazz = T;  
 }  
  
  
    @Override  
 public T handle(ResultSet resultSet) throws SQLException {  
        T t = null;  
 if(resultSet.next()){  
            try {  
                t = clazz.newInstance();  
 ResultSetMetaData metaData = resultSet.getMetaData();  
 int columnCount = metaData.getColumnCount();  
 for(int i = 1; i <= columnCount; i++){  
                    String columnName = metaData.getColumnName(i);  
 Object columnValue = resultSet.getObject(columnName);  
 try {  
                        Field field = clazz.getDeclaredField(columnName);  
 field.setAccessible(true); // 获取拜访操作权限  
 field.set(t, columnValue);  
 }catch (NoSuchFieldException e){  
                        e.printStackTrace();  
 }  
                }  
            } catch (InstantiationException | IllegalAccessException e) {  
                e.printStackTrace();  
 }  
        }  
        return t;  
 }  
  
}

1. 对于后果集为多个,须要用List来接管,同样用一个接口来继承MyResultSetHandler并实现即可,本文就不再做演示。
2. 减少测试类Account,数据库也该当存在此表即一些测试数据。次要有以下字段：

private int id;  
private String name;  
private Double money;
//留神：mysql中定义decimal字段,应由BigDecimal来接管

1. 测试

public static void main(String[] args)  {  
    MyRunner myRunner= new MyRunner(JdbcUtil.getDataSource());  
 Account account = myRunner.query("SELECT * FROM account WHERE id =?;",new MyBeanHandler<Account>(Account.class),1);  
 System.out.println(account);  
 List<Account> accounts = myRunner.query("SELECT * FROM account",new MyBeanListHandler<>(Account.class));  
 System.out.println(accounts);  
}