三、定义DAO实现模板类简化DAO实现类
3.1 定义和使用抽象化DAO类(模板模式)
使用继承模板DAO类来优化DAO实现类的编写:
优化查询操作,区分开变化和不变的部分:
sql和ResultSet的处理是变化部分,创建和释放资源部分是不变部分。
提取超类,将不变部分放入超类,变化部分留给子类实现。
超类的主要代码:
public Object find(String sql, Object[] args) {
…
rs = ps.executeQuery();
if (rs.next()) return rowMapper(rs);
…
}
protected abstract Object rowMapper(ResultSet rs);
package org.com.dao.refactor.template;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import org.com.dao.DAOException;
import org.com.lin.JdbcUtilsSing;
public abstract class AbstractDao{
public Object find(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtilsSing.getInstance().getConnection();
ps = conn.prepareStatement(sql);
int len=0;
if(args!=null){
len=args.length;
}
for (int i = 0;i<len; i++){
ps.setObject(i + 1, args[i]);
}
rs = ps.executeQuery();
Object obj = null;
if (rs.next()) {
obj = rowMapper(rs);
}
return obj;
} catch (SQLException e) {
throw new DAOException(e.getMessage(), e);
} finally {
JdbcUtilsSing.getInstance().free(rs, ps, conn);
}
}
abstract protected Object rowMapper(ResultSet rs) throws SQLException;
public int update(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
try {
conn = JdbcUtilsSing.getInstance().getConnection();
ps = conn.prepareStatement(sql);
int len=0;
if(args!=null){
len=args.length;
}
for (int i = 0;i<len; i++){
ps.setObject(i + 1, args[i]);
}
return ps.executeUpdate();
} catch (SQLException e) {
throw new DAOException(e.getMessage(), e);
} finally {
JdbcUtilsSing.getInstance().free(null, ps, conn);
}
}
public ResultSet insertBackPrimaryKey(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
try {
conn = JdbcUtilsSing.getInstance().getConnection();
ps = conn.prepareStatement(sql);
int len=0;
if(args!=null){
len=args.length;
}
for (int i = 0;i<len; i++){
ps.setObject(i + 1, args[i]);
}
ps.executeUpdate();
return ps.getGeneratedKeys();
} catch (SQLException e) {
throw new DAOException(e.getMessage(), e);
} finally {
JdbcUtilsSing.getInstance().free(null, ps, conn);
}
}
}
package org.com.dao.refactor.template;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import org.com.dao.DAOException;
import org.com.domain.User;
public class UserDAOImpl extends AbstractDao{
public User getUser(int userId) {
String sql="select id,name,birthday,money from user where id=?";
Object[] args=new Object[]{userId};
return (User) super.find(sql, args);
}
@Override
protected Object rowMapper(ResultSet rs) throws SQLException {
User user = new User();
user.setId(rs.getInt("id"));
user.setName(rs.getString("name"));
user.setMoney(rs.getFloat("money"));
user.setBirthday(rs.getDate("birthday"));
return user;
}
//如下两个方法要么用原来的实现方法,要么在另一个AbstractDao子类中定义重新实现rowMapper方法
//所以,这样仍然不够通用与灵活
public List findByName(String name) {
return null;
}
public String getUserName(int userId) {
return null;
}
public int update(User user) {
String sql="update user set name=?,birthday=?,money=? where id=?";
Object[] args=new Object[]{user.getName(),user.getBirthday(),user.getMoney(),user.getId()};
return super.update(sql, args);
}
public int delete(User user) {
String sql="delete from user where id=?";
Object[] args=new Object[]{user.getId()};
return super.update(sql, args);
}
public int insert(User user){
String sql="insert into user (name,birthday,money) values(?,?,?)";
Object[] args=new Object[]{user.getName(),user.getBirthday(),user.getMoney()};
return super.update(sql, args);
}
public int insertBackPrimaryKey(User user){
String sql="insert into user (name,birthday,money) values(?,?,?)";
Object[] args=new Object[]{user.getName(),user.getBirthday(),user.getMoney()};
ResultSet rs=super.insertBackPrimaryKey(sql, args);
if(rs!=null){
try {
user.setId(rs.getInt(0));
} catch (SQLException e) {
throw new DAOException(e.getMessage(), e);
}
}
return user.getId();
}
}
3.2 定义和使用抽象化DAO类(策略模式)
使用组合DAO模板类来优化DAO实现类的编写:
优化查询操作,区分开变化和不变的部分:
sql和ResultSet的处理是变化部分,创建和释放资源部分是不变部分。
提取接口封装变化部分。
JDBC操作主要代码:
public Object find(String sql, Object[] args, RowMapper rowMapper) {
…
rs = ps.executeQuery();
if (rs.next())return rowMapper.mapRow(rs);
…
}
回调接口:
public interface RowMapper {
public Object mapRow(ResultSet rs) throws SQLException;
}
package org.com.dao.refactor.strategy;
import java.sql.ResultSet;
import java.sql.SQLException;
public interface RowMapper {
Object rowMapper(ResultSet rs) throws SQLException;
}
package org.com.dao.refactor.strategy;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import org.com.dao.DAOException;
import org.com.lin.JdbcUtilsSing;
public class MyDaoTemplate{
public Object find(String sql, Object[] args,RowMapper rowMapper) {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtilsSing.getInstance().getConnection();
ps = conn.prepareStatement(sql);
int len=0;
if(args!=null){
len=args.length;
}
for (int i = 0;i<len; i++){
ps.setObject(i + 1, args[i]);
}
rs = ps.executeQuery();
Object obj = null;
if (rs.next()) {
obj = rowMapper.rowMapper(rs);
}
return obj;
} catch (SQLException e) {
throw new DAOException(e.getMessage(), e);
} finally {
JdbcUtilsSing.getInstance().free(rs, ps, conn);
}
}
public int update(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
try {
conn = JdbcUtilsSing.getInstance().getConnection();
ps = conn.prepareStatement(sql);
int len=0;
if(args!=null){
len=args.length;
}
for (int i = 0;i<len; i++){
ps.setObject(i + 1, args[i]);
}
return ps.executeUpdate();
} catch (SQLException e) {
throw new DAOException(e.getMessage(), e);
} finally {
JdbcUtilsSing.getInstance().free(null, ps, conn);
}
}
public ResultSet insertBackPrimaryKey(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
try {
conn = JdbcUtilsSing.getInstance().getConnection();
ps = conn.prepareStatement(sql);
int len=0;
if(args!=null){
len=args.length;
}
for (int i = 0;i<len; i++){
ps.setObject(i + 1, args[i]);
}
ps.executeUpdate();
return ps.getGeneratedKeys();
} catch (SQLException e) {
throw new DAOException(e.getMessage(), e);
} finally {
JdbcUtilsSing.getInstance().free(null, ps, conn);
}
}
}
package org.com.dao.refactor.strategy;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import org.com.dao.DAOException;
import org.com.domain.User;
public class UserDAOImpl{
private MyDaoTemplate template;
public User getUser(int userId) {
String sql="select id,name,birthday,money from user where id=?";
Object[] args=new Object[]{userId};
User user=(User) this.template.find(sql, args,new RowMapper(){
public Object rowMapper(ResultSet rs) throws SQLException {
User user = new User();
user.setId(rs.getInt("id"));
user.setName(rs.getString("name"));
user.setMoney(rs.getFloat("money"));
user.setBirthday(rs.getDate("birthday"));
return user;
}
});
return user;
}
public List findByName(String name) {
String sql="select id,name,birthday,money from user where name=?";
Object[] args=new Object[]{name};
List all=(List) this.template.find(sql, args,new RowMapper(){
public Object rowMapper(ResultSet rs) throws SQLException {
List all=new ArrayList();
while(rs.next()){
User user = new User();
user.setId(rs.getInt("id"));
user.setName(rs.getString("name"));
user.setMoney(rs.getFloat("money"));
user.setBirthday(rs.getDate("birthday"));
all.add(user);
}
return all;
}
});
return all;
}
public String getUserName(int userId) {
String sql="select name from user where id=?";
Object[] args=new Object[]{userId};
String name=(String) this.template.find(sql, args,new RowMapper(){
public Object rowMapper(ResultSet rs) throws SQLException {
return rs.getObject("name");
}
});
return name;
}
public int update(User user) {
String sql="update user set name=?,birthday=?,money=? where id=?";
Object[] args=new Object[]{user.getName(),user.getBirthday(),user.getMoney(),user.getId()};
return this.template.update(sql, args);
}
public int delete(User user) {
String sql="delete from user where id=?";
Object[] args=new Object[]{user.getId()};
return this.template.update(sql, args);
}
public int insert(User user){
String sql="insert into user (name,birthday,money) values(?,?,?)";
Object[] args=new Object[]{user.getName(),user.getBirthday(),user.getMoney()};
return this.template.update(sql, args);
}
public int insertBackPrimaryKey(User user){
String sql="insert into user (name,birthday,money) values(?,?,?)";
Object[] args=new Object[]{user.getName(),user.getBirthday(),user.getMoney()};
ResultSet rs=this.template.insertBackPrimaryKey(sql, args);
if(rs!=null){
try {
user.setId(rs.getInt(0));
} catch (SQLException e) {
throw new DAOException(e.getMessage(), e);
}
}
return user.getId();
}
}
JDBC工具类
最新推荐文章于 2021-04-09 23:27:06 发布