数据库查询的优化

查询一个实体的优化步骤：

1.创建gerRs(),参考代码如下

public static ResultSet getRs(String sql, Object[] args) {
		Object t = null;
		Connection con = getConnection();
		PreparedStatement ps = null;
		ResultSet rs = null;
		Dao d = new Dao();
		try {
			ps = con.prepareStatement(sql);
			for (int i = 0; i < args.length; i++) {
				if (args[i].getClass() == java.util.Date.class) {
					java.util.Date date = (java.util.Date) args[i];
					ps.setDate(i + 1, new java.sql.Date(date.getTime()));
				} else if (args[i].getClass() == boolean.class || args[i] == Boolean.class) {
					ps.setInt(i + 1, (boolean) args[i] == true ? 1 : 0);
				} else {
					ps.setObject(i + 1, args[i]);
				}
				ps.setString(i + 1, (String) args[i]);
			}
			rs = ps.executeQuery();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return rs;
	}

2.创建封装实体的类，参考代码如下

package com.xxx.generic.demo;

import java.lang.reflect.Field;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;

public class BeanResultSetHandler<T> {
	private Class clazz;

	public BeanResultSetHandler(Class<T> clazz) {
		this.clazz = clazz;
	}

	public T handler(ResultSet rs) {
		T bean = null;
		try {
			if (rs.next()) {
				bean = (T) this.clazz.newInstance();
				ResultSetMetaData rsmd = rs.getMetaData();
				int totalColumns = rsmd.getColumnCount();
				Field[] fields = this.clazz.getDeclaredFields();
				for (Field f : fields) {
					String paramName = f.getName();
					for (int i = 1; i <= totalColumns; i++) {
						String columnName = rsmd.getColumnName(i);
						if (columnName.equals(paramName)) {
							Object columnValue = rs.getObject(columnName);
							f.setAccessible(true);
							if (f.getType() == java.lang.Boolean.class || f.getType() == boolean.class) {
								int n = Integer.parseInt((String) columnValue);
								f.set(bean, n == 0 ? true : false);
							} else if (f.getType() == Double.class || f.getType() == double.class) {
								f.set(bean, (double) columnValue);
							} else if (f.getType() == Float.class || f.getType() == float.class) {
								f.set(bean, (float) columnValue);
							} else {
								f.set(bean, columnValue);
							}
							break;
						}
					}
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			DbUtils.close(null, null, rs);
		}
		return bean;
	}
}

3.创建测试方法，参考代码如下

public void t2() {
		String sql = "select * from student where name=?";
		BeanResultSetHandler handler = new BeanResultSetHandler<>(Student.class);
		Student s = null;
		s = (Student) handler.handler(DbUtils.getRs(sql, new Object[] { "小张" }));
		System.out.println(s);
	}

4.相关说明

在getRs()方法中未曾释放相关的资源流。