ano*_*ous 9 java spring jdbc jdbctemplate
我有一个Java SE 8 Spring 4.1.6-RELEASE应用程序,我正在实现该org.springframework.jdbc.core.RowMapper<T>接口,我java.sql.ResultSet对其T mapRow(ResultSet rs, int rowNum)方法中传递的接口有一些疑问.
当我检查ResultSet类时,我看到了一堆方法来获取列值:
??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ? Return Type ? Method ? Return (javadoc, se 8) ? ??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ? String ? getString ? the column value; if the value is SQL NULL, the value returned is null ? ? boolean ? getBoolean ? the column value; if the value is SQL NULL, the value returned is false ? ? byte ? getByte ? the column value; if the value is SQL NULL, the value returned is 0 ? ? short ? getShort ? the column value; if the value is SQL NULL, the value returned is 0 ? ? int ? getInt ? the column value; if the value is SQL NULL, the value returned is 0 ? ? long ? getLong ? the column value; if the value is SQL NULL, the value returned is 0 ? ? float ? getFloat ? the column value; if the value is SQL NULL, the value returned is 0 ? ? double ? getDouble ? the column value; if the value is SQL NULL, the value returned is 0 ? ? BigDecimal ? getBigDecimal ? the column value; if the value is SQL NULL, the value returned is null ? ? byte[] ? getBytes ? the column value; if the value is SQL NULL, the value returned is null ? ? Date ? getDate ? the column value; if the value is SQL NULL, the value returned is null ? ? Time ? getTime ? the column value; if the value is SQL NULL, the value returned is null ? ? Timestamp ? getTimestamp ? the column value; if the value is SQL NULL, the value returned is null ? ? InputStream ? getAsciiStream ? a Java input stream that delivers the database column value as a stream of one-byte ASCII characters; if the value is SQL NULL, the value returned is null ? ? Reader ? getCharacterStream ? a java.io.Reader object that contains the column value; if the value is SQL NULL, the value returned is null in the Java programming language ? ? InputStream ? getBinaryStream ? a Java input stream that delivers the database column value as a stream of uninterpreted bytes; if the value is SQL NULL, the value returned is null ? ? <T> T ? getObject ? an instance of type holding the column value ? ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
通常的期望/做法是:
rs.getObject("COLUMN_NAME", Boolean.class);
rs.getObject("COLUMN_NAME", Byte.class);
rs.getObject("COLUMN_NAME", Short.class);
rs.getObject("COLUMN_NAME", Integer.class);
rs.getObject("COLUMN_NAME", Long.class);
等,对于所有原始类型？正如其他所有东西返回null的实例一样SQL NULL.
如果是这样,当有类型的Object方法存在时,为不同类型设置所有方法的重点是什么？
另外,每种方法的优缺点是什么？
使用getInt(String columnLabel):
Integer resultingActionId = rs.getInt("RESULTING_ACTION_ID");
if (rs.wasNull) {
resultingActionId = null
}使用getObject(String columnLabel)和转换为Integer:
Integer resultingActionId = (Integer) rs.getObject("RESULTING_ACTION_ID");使用getObject(String columnLabel, Class type):
Integer resultingActionId = rs.getObject("RESULTING_ACTION_ID", Integer.class);举例来说,我发现org.springframework.jdbc.core.JdbcTemplate以前有queryForLongqueryForIntqueryForObject方法.
谢谢!
如果你看一下java.sql.ResultSet，你会发现你不需要那么明确。实际上，除非您有一个允许您使用 getObject 方法的连接的 typeMapper，否则它将无法工作（java.sql.ResultSet.getObject）。
我不知道它是否对您有帮助，但我设法找到了自己的 RowMapper，它非常适合我的需求。
private class ShabaUserMapper implements RowMapper<ShabaUser>
{
@Override
public ShabaUser mapRow( ResultSet rs, int rowNum ) throws SQLException
{
Collection<SimpleGrantedAuthority> roles = new ArrayList<SimpleGrantedAuthority>();
String auths = rs.getString( "role" );
roles.add( new SimpleGrantedAuthority( auths ) );
ShabaUser user = new ShabaUser( rs.getString( "username" ), rs.getString( "password" ),
rs.getBoolean( "enabled" ), rs.getString( "first_name" ),
rs.getString( "last_name" ), rs.getString( "email" ),
rs.getString( "date_joined" ), rs.getString( "last_online" ), true, true, true,
roles );
// Can be null!
Integer awesomeness = rs.getInt( "awesomeness" );
if ( rs.wasNull() )
{
awesomeness = null;
}
user.setAwesomeness( awesomeness );
return user;
}
}
private class ShabaUserListExtractor implements ResultSetExtractor<List<ShabaUser>>
{
private final ShabaUserMapper rowMapper;
private int rowsExpected;
public ShabaUserListExtractor()
{
this( new ShabaUserMapper(), 0 );
}
public ShabaUserListExtractor( ShabaUserMapper rowMapper, int rowsExpected )
{
Assert.notNull( rowMapper, "RowMapper is required" );
this.rowMapper = rowMapper;
this.rowsExpected = rowsExpected;
}
@Override
public List<ShabaUser> extractData( ResultSet rs ) throws SQLException
{
HashMap<String, ShabaUser> results = ( this.rowsExpected > 0
? new HashMap<String, ShabaUser>(
rowsExpected )
: new HashMap<String, ShabaUser>() );
int rowNum = 0;
while ( rs.next() )
{
ShabaUser user = rowMapper.mapRow( rs, rowNum++ );
if ( results.containsKey( user.getUsername() ) )
{
ShabaUser inUser = results.get( user.getUsername() );
ArrayList<GrantedAuthority> combinedAuthorities = new ArrayList<GrantedAuthority>();
combinedAuthorities.addAll( inUser.getAuthorities() );
combinedAuthorities.addAll( user.getAuthorities() );
results.put( user.getUsername(),
createUserDetails( user.getUsername(), user, combinedAuthorities ) );
} else
{
results.put( user.getUsername(), user );
}
}
return new ArrayList<ShabaUser>( results.values() );
}
}
我意识到这是很多代码，但希望您能看到这里完成了什么。实际的 RowMapper 实现实际上是为了容纳从行信息中提取对象的所有“脏工作”。
只要您的数据库设置正确并且在必需的列上设置了 NOT NULL，您就永远不会遇到拉出空行的问题。虽然我认为检查 ResultSet 中的空响应不会有什么坏处，但如果该列应该有一个值，您仍然最终会抛出异常。
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