通用的增、删、改和查方法 DAO
通用的增、删、改的方法 （version 1.0 ）
public
void
update
(
String sql
){
//1.
获取数据库的连接
Connection conn
=
null
;
//2.
创建一个
Statement
对象，用来传送
sql
语句
Statement st
=
null
;
try
{
conn
=
JDBCUtils
.
getConnection
();
st
=
conn
.
createStatement
();
//3.
执行
sql
语句
st
.
execute
(
sql
);
}
catch
(
Exception e
)
{
// TODO Auto-generated catch block
e
.
printStackTrace
();
}
finally
{
//4.
关闭操作
if
(
st
!=
null
){
try
{
st
.
close
();
}
catch
(
SQLException e
)
{
// TODO Auto-generated catch block
e
.
printStackTrace
();
}
}
if
(
conn
!=
null
){
try
{
conn
.
close
();
}
catch
(
SQLException e
)
{
// TODO Auto-generated catch block
e
.
printStackTrace
();
}
}
}
}
通用的增、删、改的方法（ version 2.0 ）
public
void
update
(
String
sql
)
{
// 1.获取数据库的连接
Connection
conn
=
null;
// 2.创建一个Statement对象，用来传送 sql语句
Statement
st
=
null;
try
{
conn
=
JDBCUtils
.
getConnection
()
;
st
=
conn
.
createStatement
()
;
// 3.执行 sql语句
st
.
executeUpdate
(
sql
)
;
}
catch
(
Exception
e
)
{
e
.
printStackTrace
()
;
}
finally
{
// //4.关闭操作
JDBCUtils
.
close
(
null,
st
,
conn
)
;
}
}
通用的增、删、改的方法（ version 3.0）
public
void
update
(
Connection conn
,
String sql
,
Object
...
args
)
{
try
{
QueryRunner runner
= new QueryRunner ();
runner
.
update
(
conn
,
sql
,
args
);
}
catch
(
SQLException e
)
{
e
.
printStackTrace
();
}
}
使用QueryRunner 类
通用的查询方法，返回一个对象【代码少】
public
T getInstance
(
Connection conn
,
String sql
,
Object
...
args
)
{
try
{
QueryRunner runner
= new QueryRunner ();
ResultSetHandler
<
T
>
handler
=
new
BeanHandler
<
T
>(
clazz
); //clazz怎么来的？请向下看
return
runner
.
query
(
conn
,
sql
,
handler
,
args
);
}
catch
(
Exception e
)
{
e
.
printStackTrace
();
return
null
;
}
通用的查询方法，返回多个对象【代码少】
【MapListHandler 】
public
List
<
T
>
getForList1
(
Connection conn
,
String sql
,
Object
...
args
)
{
QueryRunner runner
=
new
QueryRunner
();
try
{
ResultSetHandler
<
List
<
Map
<
String
,
Object
>>>
handler
=
new
MapListHandler
();
List
<
Map
<
String
,
Object
>>
map
=
runner
.
query
(
conn
,
sql
,
handler
);
return
(
List
<
T
>)
map
;
}
catch
(
Exception e
)
{
e
.
printStackTrace
();
}
return
null
;
}
【BeanListHandler】
public
List
<
T
>
getForList2
(
Connection conn
,
String sql
,
Object
...
args
)
{
QueryRunner runner
=
new
QueryRunner
();
try
{
ResultSetHandler
<
List
<
T
>>
handler
=
new
BeanListHandler
<
T
>(
clazz
);
List
<
T
>
list
=
runner
.
query
(
conn
,
sql
,
handler
);
return
list
;
}
catch
(
Exception e
)
{
e
.
printStackTrace
();
}
return
null
;
}
此处的clazz来自于--->
public
class
DAO
<
T
>
{
Class
<
T
>
clazz
=
null
;
public
DAO
()
{
//
此处的
this
相当于正在创建的
customerDAO
对象
clazz
=
ReflectionUtils
.
getSuperClassGeneric
(
this
.
getClass
());
}
此处的ReflectionUtils来自于--->
class
ReflectionUtils
{
//
如何获取形参
clazz
的父类的泛型
public
static
Class getSuperClassGeneric
(
Class clazz
)
{
Type t
=
clazz
.
getGenericSuperclass
();
ParameterizedType type
=
(
ParameterizedType
)
t
;
Type
[]
types
=
type
.
getActualTypeArguments
();
return
(
Class
)
types
[
0
];
}
}
查询某些特殊数值的数据
public
<
E
>
E getValue1
(
Connection conn
,
String sql
,
Object
...
args
){
try
{
ResultSetHandler
<
Object
>
handler
=
new
ScalarHandler
();
QueryRunner runner
=
new
QueryRunner
();
Object obj
=
runner
.
query
(
conn
,
sql
,
handler
,
args
);
return
(
E
)
obj
;
}
catch
(
Exception e
)
{
e
.
printStackTrace
();
}
return
null
;
}
之前的查询方法（代码量大）
//
通用的查询方法，返回一个对象
public T getInstance (Connection conn , String sql , Object... args) {
PreparedStatement ps = null;
ResultSet rs = null;
T t = null;
try {
ps = conn .prepareStatement (sql );
for (int i = 0; i < args.length; i++) {
ps .setObject (i + 1, args[i]);
}
rs = ps .executeQuery ();
ResultSetMetaData rsmd = rs .getMetaData ();
int columnCount = rsmd .getColumnCount ();
t = null;
if (rs .next ()) {
t = clazz .newInstance ();
for (int i = 0; i < columnCount; i++) {
Object columnVal = rs .getObject (i + 1);
String columnLabel = rsmd.getColumnLabel( i + 1);
PropertyUtils .setProperty (t , columnLabel, columnVal);
}
}
} catch (Exception e ) {
e .printStackTrace ();
} finally {
JDBCUtils .close (rs , ps , null);
}
return t ;
}
//通用的查询方法，返回一个包含多个对象的集合(练习)
public
List
<
T
>
getForList
(
Connection
conn
,
String
sql
,
Object
...
args
)
{
PreparedStatement
ps
=
null;
ResultSet
rs
=
null;
List
<
T
>
list
=
null ;
T
t
=
null;
try
{
ps
=
conn
.
prepareStatement
(
sql
)
;
for
(
int
i
=
0
;
i
<
args
.
length
;
i
++
)
{
ps
.
setObject
(
i
+
1
,
args
[
i
])
;
}
rs
=
ps
.
executeQuery
()
;
ResultSetMetaData
rsmd
=
rs
.
getMetaData
()
;
int
columnCount
=
rsmd
.
getColumnCount
()
;
t
=
null ;
list
=
new
ArrayList
<
T
>
()
;
while
(
rs
.
next
())
{
t
=
clazz
.
newInstance
()
;
for
(
int
i
=
0
;
i
<
columnCount
;
i
++
)
{
Object
columnVal
=
rs
.
getObject
(
i
+
1
)
;
String
columnLabel
=
rsmd
.
getColumnLabel
(
i
+
1
)
;
PropertyUtils
.
setProperty
(
t
,
columnLabel
,
columnVal
)
;
}
list
.
add
(
t
)
;
}
}
catch
(
Exception
e
)
{
e
.
printStackTrace
()
;
}
finally
{
JDBCUtils
.
close
(
rs
,
ps
,
null
)
;
}
return
list
;
}