JDBC用到了哪些设计模式
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发布时间：2022-04-08 18:01
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时间：2022-04-08 22:22
class DAO {
public int update(String sql, Object ... args){
Connection conn = null;
PreparedStatement ps = null;
int rowNum = 0;
try{
conn = JDBCUtils.getConnection();
ps = conn.prepareStatement(sql);
for(int i = 0; i < args.length; i++){
ps.setObject(i + 1, args[i]);
}
rowNum = ps.executeUpdate();
return rowNum;
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.release(conn, ps, null);
}
return rowNum;
}
public <T> T get(Class<T> clazz, String sql, Object ...args){
T entity = null;
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();
Map<String, Object> map = new HashMap<String, Object>();
List<String> columnLabels = getColumnLabels(rs);
if(rs.next()){
for(String columnLabel : columnLabels){
Object columnValue = rs.getObject(columnLabel);
map.put(columnLabel, columnValue);
}
}
if(map.size() > 0){
entity = clazz.newInstance();
for(Map.Entry<String, Object> entry : map.entrySet()){
String fieldName = entry.getKey();
Object value = entry.getValue();
//使用BeanUtils工具类来为属性赋值
BeanUtils.setProperty(entity, fieldName, value);
/**使用反射的方式为属性赋值
Field field = clazz.getDeclaredField(key);
field.setAccessible(true);
field.set(entity, value);*/
}
return entity;
}
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.release(conn, ps, rs);
}
return entity;
}
public <T> List<T> getForList(Class<T> clazz, String sql, Object ... args){
List<T> list = new ArrayList<>();
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();
/**
* 将得到的ResultSet结果集转换为Map<String, Object>列表，
* 其中key值为rs表的别名，value值为对应别名的值
*/
List<Map<String, Object>> data = handleResultSetToMapList(rs);
/**
* 将MapList转换为对应的BeanList
*/
list = transferMapListToBeanList(clazz, data);
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.release(conn, ps, rs);
}
return list;
}
private <T> List<T> transferMapListToBeanList(Class<T> clazz,List<Map<String, Object>> data) throws Exception {
List<T> list = new ArrayList<>();
if(data.size() > 0){
for(Map<String, Object> map : data){
T entity = clazz.newInstance();
for(Map.Entry<String, Object> entry : map.entrySet()){
String fieldName = entry.getKey();
Object value = entry.getValue();
BeanUtils.setProperty(entity, fieldName, value);;
}
list.add(entity);
}
}
return list;
}
public static <E> E getForValue(String sql, Object ... args){
E entity = null;
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();
if(rs.next()){
return (E)rs.getObject(1);
}
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.release(conn, ps, rs);
}
return entity;
}
/**
* 将获取到的结果集处理成MapList
* @param rs
* @return
* @throws Exception
*/
private List<Map<String, Object>> handleResultSetToMapList(ResultSet rs)
throws Exception {
List<String> columnLabels = getColumnLabels(rs);
List<Map<String, Object>> data = new ArrayList<Map<String, Object>>();
while(rs.next()){
Map<String, Object> map = new HashMap<String, Object>();
for(String columnLabel : columnLabels){
Object columnValue = rs.getObject(columnLabel);
map.put(columnLabel, columnValue);
}
data.add(map);
}
return data;
}
/**
* 根据结果集获取所有列的别名
* @param rs
* @return
* @throws Exception
*/
private List<String> getColumnLabels(ResultSet rs) throws Exception{
List<String> list = new ArrayList<>();
ResultSetMetaData rsmd = rs.getMetaData();
for(int i = 0; i < rsmd.getColumnCount(); i++){
list.add(rsmd.getColumnLabel(i + 1));
}
return list;
}
}
JDBC--DAO设计模式
标签：
热心网友
时间：2022-04-08 19:30
至少有：
1. 静态工厂
DriverManager.getConnection(...)
2. 单例
DriverManager.getDriver(...)
3. 针对resultset及其子类/接口，有不少修饰模式
