用JDBC封装CRUD操作（个人总结）

先定义好实体类，我简化了属性：

package org.lmw.crud.po;
/**
*
* <br/>Copyright (C), 2010, Mingwei Liu
* <br/>This program is protected by copyright laws.
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 30, 2010 10:48:36 PM
*
*/
public class User {
private int id;
private String name;

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;
}

@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + id;
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
User other = (User) obj;
if (id != other.id)
return false;
return true;
}

}

然后定义接口：

package org.lmw.crud.po.dao;
import org.lmw.crud.po.User;
/**
*
* <br/>Copyright (C), 2010, Mingwei Liu
* <br/>This program is protected by copyright laws.
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 30, 2010 10:52:54 PM
*
*/
public interface UserDao {

public void save(User user);

public boolean delete(User user);

public void update(User user);

public User selectByName(String name);

}

初学JDBC时，都没个dao自己获得数据库连接，自己执行SQL语句，自己关闭资源，这样有两个缺陷。

第一SQL异常无法处理，第二大量的代码是重复的。

第一个问题我们可以定义一个DaoException继承RuntimeException，这样上层就不用捕获SQL异常了。即使换成文件存储数据，也不用更改Service层的代码，真正做到了各层之间的解耦。

第二个问题可以使用Template模式解决。

定义DaoException的代码：

package com.hp.trainermanage.dao.impl;
/**
*Root of the hierarchy of data access exceptions.
* <p>
* As this class is a runtime exception, there is no need for user code to catch
* it or subclasses if any error is to be considered fatal (the usual case). <br/>
* Copyright (C), 2010, Mingwei Liu <br/>
* This program is protected by copyright laws.
*
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 9, 2010 4:26:19 PM
*/
public class DaoException extends RuntimeException {
private static final long serialVersionUID = 6260282384874832029L;
/**
* Constructor for DaoException.
*
*/
public DaoException() {
}
/**
* Constructor for DaoException.
*
* @param message
*            the detail exception message
*/
public DaoException(String message) {
super(message);
}
/**
* Constructor for DaoException.
*
* @param cause
*            the root cause
*/
public DaoException(Throwable cause) {
super(cause);
}
/**
* Constructor for DaoException.
*
* @param message
*            the detail exception message
* @param cause
*            the root cause
*/
public DaoException(String message, Throwable cause) {
super(message, cause);
}
}

定义与数据库打交道的接口：

package com.hp.trainermanage.dao.impl;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
/**
*
* <br/>Copyright (C), 2010, Mingwei Liu
* <br/>This program is protected by copyright laws.
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 28, 2010 10:42:47 AM
*/
public interface JdbcUtil {

/**
*
* @return
* @throws SQLException
*/
public Connection getConnection() throws SQLException;

/**
*
* @param rs
* @param st
* @param conn
*/
public void free(ResultSet rs, Statement st, Connection conn);
}

MySQL实现：

package com.hp.trainermanage.dao.impl;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
import javax.sql.DataSource;
import org.apache.commons.dbcp.BasicDataSourceFactory;
/**
*
* <br/>
* Copyright (C), 2010, Mingwei Liu <br/>
* This program is protected by copyright laws.
*
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 9, 2010 7:33:40 PM
*/
public final class JdbcUtilMySQLImpl implements JdbcUtil {
private static DataSource dataSource = null;
static {
try {
Properties properties = new Properties();
InputStream is = JdbcUtilMySQLImpl.class.getClassLoader()
.getResourceAsStream("jdbc.properties");
properties.load(is);
dataSource = BasicDataSourceFactory.createDataSource(properties);
} catch (Exception e) {
throw new ExceptionInInitializerError(e);
}
}

public DataSource getDataSource() {
return dataSource;
}
@Override
public Connection getConnection() throws SQLException {
return dataSource.getConnection();
}
@Override
public void free(ResultSet rs, Statement st, Connection conn) {
try {
if (rs != null)
rs.close();
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (st != null)
st.close();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (conn != null)
try {
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}

定义JdbcTemplate类：

package com.hp.trainermanage.dao.impl;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.LinkedList;
import java.util.List;
import org.apache.log4j.Logger;
/**
*
* <br/>
* Copyright (C), 2010, Mingwei Liu <br/>
* This program is protected by copyright laws.
*
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 10, 2010 8:21:34 AM
*
*/
public class JdbcTemplate {
JdbcUtil jdbcUtil = new JdbcUtilMySQLImpl();
private static Logger logger = Logger.getLogger(JdbcTemplate.class);
public Object query(String sql, Object[] args, RowMapper rowMapper) {
Connection connection = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
connection = jdbcUtil.getConnection();
pstmt = connection.prepareStatement(sql);
if (args != null) {
for (int i = 0; i < args.length; i++) {
pstmt.setObject(i + 1, args[i]);
}
}
rs = pstmt.executeQuery();
Object obj = null;
if (rs.next()) {
obj = rowMapper.mapRow(rs);
}
return obj;
} catch (SQLException e) {
logger.error(e);
throw new DaoException(e.getMessage(), e);
} finally {
jdbcUtil.free(rs, pstmt, connection);
}
}
public List<Object> queryForList(String sql, Object[] args,
RowMapper rowMapper) {
Connection connection = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
connection = jdbcUtil.getConnection();
pstmt = connection.prepareStatement(sql);
if (args != null) {
for (int i = 0; i < args.length; i++) {
pstmt.setObject(i + 1, args[i]);
}
}
rs = pstmt.executeQuery();
List<Object> objects = new LinkedList<Object>();
while (rs.next()) {
Object obj = rowMapper.mapRow(rs);
objects.add(obj);
}
return objects;
} catch (SQLException e) {
logger.error(e);
throw new DaoException(e.getMessage(), e);
} finally {
jdbcUtil.free(rs, pstmt, connection);
}
}
public int executeUpdate(String sql, Object[] args) {
Connection connection = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
connection = jdbcUtil.getConnection();
pstmt = connection.prepareStatement(sql);
for (int i = 0; i < args.length; i++) {
pstmt.setObject(i + 1, args[i]);
}
return pstmt.executeUpdate();
} catch (SQLException e) {
logger.error(e);
throw new DaoException(e.getMessage(), e);
} finally {
jdbcUtil.free(rs, pstmt, connection);
}
}
}

定义SuperDao所有dao的父类：

package com.hp.trainermanage.dao.impl;
/**
*
* <br/>Copyright (C), 2010, Mingwei Liu
* <br/>This program is protected by copyright laws.
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 10, 2010 6:14:34 PM
*
*/
public class SuperDao {

private JdbcTemplate jdbcTemplate = new JdbcTemplate();
public JdbcTemplate getJdbcTemplate() {
return jdbcTemplate;
}
}

定义代表对象和记录的映射的接口RowMapper：

package com.hp.trainermanage.dao.impl;
import java.sql.ResultSet;
import java.sql.SQLException;
/**
* An interface used by {@link JdbcTemplate} for mapping rows of a
* {@link java.sql.ResultSet} on a per-row basis.
* <br/>Copyright (C), 2010, Mingwei Liu
* <br/>This program is protected by copyright laws.
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 10, 2010 8:17:21 AM
*/
public interface RowMapper {

/**
* Implementations must implement this method to map each row of data
* in the ResultSet.
* @param rs the ResultSet to map (pre-initialized for the current row)
* @return the result object for the current row
* @throws SQLException if a SQLException is encountered getting
*/
public Object mapRow(ResultSet rs) throws SQLException;
}

最后实现UserDao：

package org.lmw.crud.po.dao.impl;
import java.sql.ResultSet;
import java.sql.SQLException;
import org.lmw.crud.po.User;
import org.lmw.crud.po.dao.UserDao;
/**
*
* <br/>Copyright (C), 2010, Mingwei Liu
* <br/>This program is protected by copyright laws.
* @author Mingwei Liu E-mail:liumingweiweiwei@126.com
* @version v1.0 Date Created：Jul 30, 2010 11:07:23 PM
*
*/
public class UserDaoImpl extends SuperDao implements UserDao, RowMapper {
@Override
public void delete(User user) {
String sql = "delete from t_user where name=?";
Object[] args = new Object[] {user.getName()};
getJdbcTemplate().executeUpdate(sql, args);
}
@Override
public void save(User user) {
String sql = "insert into t_user values(null, ?)";
Object[] args = new Object[] {user.getName()};
getJdbcTemplate().executeUpdate(sql, args);

}
@Override
public User selectByName(String name) {
String sql = "select id, name from t_user where name=?";
Object[] args = new Object[] {name};
return  (User) getJdbcTemplate().query(sql, args, this);
}
@Override
public void update(User user) {
String sql = "update t_user set name=? where id=?";
Object[] args = new Object[] {user.getName(),user.getId()};
getJdbcTemplate().executeUpdate(sql, args);
}
@Override
public Object mapRow(ResultSet rs) throws SQLException {
return new User(rs.getInt("id"), rs.getString("name"));
}

}

最后上个整体架构的类图：