【web】赵雅智_框架技术
使用元数据简化JDBC代码
- 业务背景：系统中所有实体对象都涉及到基本的CRUD操作：
- 所有实体的CUD操作代码基本相同，仅仅发送给数据库的SQL语句不同而已，因此可以把CUD操作的所有相同代码抽取到工具类的一个update方法中，并定义参数接收变化的SQL语句。
- 实体的R操作，除SQL语句不同之外，根据操作的实体不同，对ResultSet的映射也各不相同，因此可义一个query方法，除以参数形式接收变化的SQL语句外，可以使用策略模式由qurey方法的调用者决定如何把ResultSet中的数据映射到实体对象中。
原方法：
ZSGC.java
package com.hbsi.yuan;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import org.junit.Test;
import com.hbsi.util.DBManager_c3p0;
public class ZSGC {
@Test
public void insert(){
Connection conn = null;
PreparedStatement st = null;
try{
conn = DBManager_c3p0.getConnection();
String sql ="insert into admin(id,name,pass)values(?,?,?)";
st = conn.prepareStatement(sql);
st.setInt(1,13);
st.setString(2,"aa");
st.setString(3,"aaa");
st.executeUpdate();
}catch(Exception e){
e.printStackTrace();
}finally{
DBManager_c3p0.closeDB(conn, st, null);
}
}
@Test
public void update(){
Connection conn = null;
PreparedStatement st = null;
try{
conn = DBManager_c3p0.getConnection();
String sql ="update admin set name=?,pass=? where id=?";
st = conn.prepareStatement(sql);
st.setString(1,"bb");
st.setString(2,"bbb");
st.setInt(3,13);
st.executeUpdate();
}catch(Exception e){
e.printStackTrace();
}finally{
DBManager_c3p0.closeDB(conn, st, null);
}
}
@Test
public void delete(){
Connection conn = null;
PreparedStatement st = null;
try{
conn = DBManager_c3p0.getConnection();
String sql ="delete from admin where id=?";
st = conn.prepareStatement(sql);
st.setInt(1,13);
st.executeUpdate();
}catch(Exception e){
e.printStackTrace();
}finally{
DBManager_c3p0.closeDB(conn, st, null);
}
}
@Test
public void find(){
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try{
conn = DBManager_c3p0.getConnection();
String sql ="select id,name,pass,sex,role from admin where id=?";
st = conn.prepareStatement(sql);
st.setInt(1,1);
rs = st.executeQuery();
while(rs.next()){
System.out.println(rs.getInt(1));
System.out.println(rs.getString(2));
System.out.println(rs.getString(3));
System.out.println(rs.getString(4));
System.out.println(rs.getInt(5));
}
}catch(Exception e){
e.printStackTrace();
}finally{
DBManager_c3p0.closeDB(conn, st, null);
}
}
}
原表数据
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使用元数据简化代码：
util下新建ResultSetHandler接口
ResultSetHandler.java
package com.hbsi.util;
import java.sql.ResultSet;
public interface ResultSetHandler {
public Object handler(ResultSet rs);
}
单行封装到一个bean对象里，多行，封装到list集合中
写好处理器
BeanHandler.java
package com.hbsi.util;
import java.lang.reflect.Field;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
public class BeanHandler implements ResultSetHandler{
//代表bin
private Class clazz;
public BeanHandler(Class clazz){
this.clazz = clazz;
}
public Object handler(ResultSet rs) {
//要把结果集封装到bean中
try{
if(!rs.next()){
return null;
}
//获取bean对象
Object bean = clazz.newInstance();
//并不知道有哪些字段，结果集的元数据
ResultSetMetaData meta = rs.getMetaData();
//用元数据获取，获得列数
int count = meta.getColumnCount();
//通过循环把bean的值和字段名取到
for(int i=0;i<count;i++){
//得到结果集中地每列字段名
String columnName = meta.getColumnName(i+1);
//按名字走，获取对应值
Object value= rs.getObject(columnName);
//反射bean上与列名相对应得属性
Field f = bean.getClass().getDeclaredField(columnName);
//权限
f.setAccessible(true);
f.set(bean, value);
}
return bean;
}catch(Exception e){
throw new RuntimeException(e);
}
}
}
DBManager_c3p0.java
package com.hbsi.util;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import com.mysql.jdbc.Statement;
public class DBManager_c3p0 {
private static ComboPooledDataSource ds = null;
static{
try{
//创建连接池
ds = new ComboPooledDataSource("mysql");
}catch(Exception e){
e.printStackTrace();
}
}
public static Connection getConnection() throws SQLException{
return ds.getConnection();
}
public static void closeDB(Connection con,PreparedStatement ps,ResultSet rs){
if(rs!=null){
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(ps!=null){
try {
ps.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(con!=null){
try {
con.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
//优化CUD操作
public static void update(String sql,Object[] params){
Connection conn = null;
PreparedStatement st = null;
try{
conn = DBManager_c3p0.getConnection();
st = conn.prepareStatement(sql);
for(int i=0;i<params.length;i++){
st.setObject(i+1, params[i]);
}
st.executeUpdate();
}catch(Exception e){
e.printStackTrace();
}finally{
DBManager_c3p0.closeDB(conn, st, null);
}
}
//
public static Object query(String sql,Object[] params, ResultSetHandler h){
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try{
conn = DBManager_c3p0.getConnection();
st = conn.prepareStatement(sql);
for(int i=0;i<params.length;i++){
st.setObject(i+1, params[i]);
}
rs = st.executeQuery();
return h.handler(rs);
}catch(Exception e){
throw new RuntimeException(e);
}finally{
DBManager_c3p0.closeDB(conn, st, rs);
}
}
}
Admin,java
package www.hbsi.domain;
import java.io.Serializable;
/**
* 把一个表admin映射(mapping)成Class类
*
* @author redarmy
*
*/
//可序列化的接口
public class Admin implements Serializable {
private static final long serialVersionUID = 1L;
// 把admin表中的字段映射成Admin类的成员属性(字段类型的转换如下 int --int Integer,varchar--String )
private int id;
private String name;
private String pass;
private String sex;
private int role;
public Admin(int id, String name, String pass, String sex, int role) {
super();
this.id = id;
this.name = name;
this.pass = pass;
this.sex = sex;
this.role = role;
}
//构造器
public Admin() {
super();
// TODO Auto-generated constructor stub
}
public Admin(String name, String pass, String sex, int role) {
super();
this.name = name;
this.pass = pass;
this.sex = sex;
this.role = role;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPass() {
return pass;
}
public void setPass(String pass) {
this.pass = pass;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public int getRole() {
return role;
}
public void setRole(int role) {
this.role = role;
}
@Override
public String toString() {
return "Admin [id=" + id + ", name=" + name + ", pass=" + pass
+ ", role=" + role + ", sex=" + sex + "]";
}
}
YouHuaZSGC.java
package com.hbsi.yuan;
import org.junit.Test;
import www.hbsi.domain.Admin;
import com.hbsi.util.BeanHandler;
import com.hbsi.util.DBManager_c3p0;
public class YouHuaZSGC {
@Test
public void insert(){
String sql ="insert into admin(id,name,pass)values(?,?,?)";
Object[] params ={13,"abc","abc"};
DBManager_c3p0.update(sql, params);
}
@Test
public void update(){
String sql ="update admin set name=?,pass=? where id=?";
Object[] params ={"xxx","xxxx",13};
DBManager_c3p0.update(sql, params);
}
@Test
public void delete(){
String sql ="delete from admin where id=?";
Object[] params ={13};
DBManager_c3p0.update(sql, params);
}
@Test
public void find(){
//单行封装到一个bean对象里，多行，封装到list集合中
String sql ="select id,name,pass from admin where id=?";
Object[] params ={4};
Admin users = (Admin) DBManager_c3p0.query(sql, params, new BeanHandler(Admin.class));
System.out.println(users.getId()+":"+users.getName()+":"+users.getPass());
}
}
原表
增加
修改
删除
查找
查询所有：
BeanListHandler.java
package com.hbsi.util;
import java.lang.reflect.Field;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;
public class BeanListHandler implements ResultSetHandler {
private Class clazz;
public BeanListHandler(Class clazz) {
super();
this.clazz = clazz;
}
public Object handler(ResultSet rs) {
try{
List list = new ArrayList();
while(rs.next()){
Object bean = clazz.newInstance();
ResultSetMetaData meta = rs.getMetaData();
int count = meta.getColumnCount();
for(int i=0;i<count;i++){
String columnName = meta.getColumnName(i+1);
Object value= rs.getObject(columnName);
Field f = bean.getClass().getDeclaredField(columnName);
f.setAccessible(true);
f.set(bean, value);
}
list.add(bean);
}
return list;
}catch(Exception e){
throw new RuntimeException(e);
}
}
}
YouHuaZSGC.java
package com.hbsi.yuan;
import java.util.List;
import org.junit.Test;
import com.hbsi.domain.Admin;
import com.hbsi.util.BeanHandler;
import com.hbsi.util.BeanListHandler;
import com.hbsi.util.DBManager_c3p0;
public class YouHuaZSGC {
@Test
public void findAll(){
//单行封装到一个bean对象里，多行，封装到list集合中
String sql ="select id,name,pass,sex,role from admin";
Object[] params ={};
List<Admin> list = (List<Admin>) DBManager_c3p0.query(sql, params, new BeanListHandler(Admin.class));
for(Admin admins:list){
System.out.println(admins.getId()+"--"+admins.getName()+"--"+admins.getPass());
}
System.out.println(list.size());
}
}
