在使用JDBC时，会重复的写很多重复的代码，例如
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
String sql="insert into t_user(username,brithday) values(?,?)";
try {
conn = JdbcUtils.getConnection();
ps = conn.prepareStatement(sql);
} catch (SQLException e) {
throw new DaoException(e.getMessage(), e);
} finally {
JdbcUtils.free(rs, ps, conn);
}
这部分代码在数据库操作方法中都会有。因此我们可以把这部分不变的内容提取出来，作为一个公用的方法。
例如，我们的增，删，改操作可以这样写
/**
* 增，删，改方法
* @param sql
* @param args sql参数
* @return
*/
public int update(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
ps = conn.prepareStatement(sql);
for (int i = 0; i < args.length; i++)
ps.setObject(i + 1, args[i]);
return ps.executeUpdate();
} catch (SQLException e) {
throw new DaoException(e.getMessage(), e);
} finally {
JdbcUtils.free(rs, ps, conn);
}
}
最麻烦的就是返回一个对象的操作了。因为我不知道要返回的对象是什么，所以在往对象里设值的时候就不确定了。因此我们可以在这个类里面定义一个抽象的方法，具体怎么实现，它的子类知道。
因此我们的这个类就可以这样设计了
package com.zzg.jdbc.base;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.zzg.jdbc.exception.DaoException;
import com.zzg.jdbc.util.JdbcUtils;
public abstract class BaseDao {
/**
* 增，删，改方法
* @param sql
* @param args sql参数
* @return
*/
public int update(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
ps = conn.prepareStatement(sql);
for (int i = 0; i < args.length; i++)
ps.setObject(i + 1, args[i]);
return ps.executeUpdate();
} catch (SQLException e) {
throw new DaoException(e.getMessage(), e);
} finally {
JdbcUtils.free(rs, ps, conn);
}
}
/**
* 返回一个对象
* @param <T>
* @param sql
* @param args
* @return
*/
public <T> T find(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
ps = conn.prepareStatement(sql);
for (int i = 0; i < args.length; i++)
ps.setObject(i + 1, args[i]);
rs = ps.executeQuery();
T t = null;
if (rs.next()) {
t = rowMapper(rs);
}
return t;
} catch (SQLException e) {
throw new DaoException(e.getMessage(), e);
} finally {
JdbcUtils.free(rs, ps, conn);
}
}
/**
* 返回一个List
* @param <T>
* @param sql
* @param args
* @return
*/
public <T> List<T> list(String sql, Object[] args) {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
ps = conn.prepareStatement(sql);
for (int i = 0; i < args.length; i++)
ps.setObject(i + 1, args[i]);
rs = ps.executeQuery();
T t = null;
List<T> list = new ArrayList<T>();
while (rs.next()) {
t = rowMapper(rs);
list.add(t);
}
return list;
} catch (SQLException e) {
throw new DaoException(e.getMessage(), e);
} finally {
JdbcUtils.free(rs, ps, conn);
}
}
abstract protected <T> T rowMapper(ResultSet rs) throws SQLException;
}
在使用时我们的类只需要继承上面那个类就可以了。
package com.zzg.jdbc.dao.impl;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import com.zzg.jdbc.base.BaseDao;
import com.zzg.jdbc.dao.UserDao;
import com.zzg.jdbc.domain.User;
public class UserDaoImpl extends BaseDao implements UserDao {
@Override
public User findUser(int id) {
String sql = "select *from t_user where id=?";
Object[] args = new Object[] { id };
User user = super.find(sql, args);
return user;
}
@Override
public List<User> listUser(String username) {
String sql = "select *from t_user where username=?";
Object[] args = new Object[] { username };
List<User> list = super.list(sql, args);
for (User u : list) {
System.out.println(u.getId());
}
return list;
}
@Override
protected Object rowMapper(ResultSet rs) throws SQLException {
User user = new User();
user.setId(rs.getInt("id"));
user.setUsername(rs.getString("username"));
user.setBrithday(rs.getDate("brithday"));
return user;
}
}
附加分页的方法：
/**
* 分页
* @param tableName
* @param PK
* @param methodPageNum
* @param methodNumPerPage
* @param conditions
* @param <T>
* @return
* @throws SQLException
*/
public <T> List<T> getPageListResultSet(String tableName,String PK,int methodPageNum,int methodNumPerPage,Map<String,String> conditions) throws SQLException{
int pageNum = methodPageNum==0?DEFAULT_PAGE_NUM:methodPageNum;
int numPerPage = methodNumPerPage==0?DEFAULT_NUM_PER_PAGE:methodNumPerPage;
List<T> list = null;
DataSetOp dataSetOp = null;
try {
dataSetOp = new DataSetOp();
String PAGE_SQL_PREFIX = " SELECT * FROM (SELECT ROW_NUMBER() OVER(ORDER BY t1.ID DESC) AS ROW_NUM, t1.* FROM ";
String PAGE_SQL_END = " ) TT WHERE TT.ROW_NUM >? AND TT.ROW_NUM <= ? ";
if(StringUtil.isNotBlank(PK)){
PAGE_SQL_PREFIX = PAGE_SQL_PREFIX.replace("ID",PK);
}
StringBuffer sql = new StringBuffer(PAGE_SQL_PREFIX);
sql.append(tableName).append(" t1 WHERE 1=1 ");
//设置条件
if(conditions!=null && conditions.size()>0){
Set<String> key = conditions.keySet();
for (Iterator it = key.iterator(); it.hasNext();) {
String column = (String) it.next();
//System.out.println(conditions.get(s));
StringBuffer cd = new StringBuffer(" and t1.");
cd.append(column).append("=‘").append(conditions.get(column)).append("‘ ");
sql.append(cd);
}
}
sql.append(PAGE_SQL_END);
System.out.println(sql);
PreparedStatement ps = dataSetOp.getConnection().prepareStatement(sql.toString());
ps.setInt(1, (pageNum - 1) * numPerPage);
ps.setInt(2, pageNum*numPerPage);
ResultSet rs = ps.executeQuery();
T t = null;
list = new ArrayList<T>();
while (rs.next()) {
t = rowMapper(rs);
list.add(t);
}
} catch (DataException e) {
e.printStackTrace();
}finally{
if(dataSetOp != null) dataSetOp.close();
}
return list;
}
时间： 2024-10-27 04:01:23