我有一个 Java SE 8 Spring 4.1.6-RELEASE 应用程序，我正在其中实现 org.springframework.jdbc.core.RowMapper<T> 界面，我对 java.sql.ResultSet 有一些疑问在其 T mapRow(ResultSet rs, int rowNum) 中传递的接口(interface)方法。
当我检查 ResultSet类，我看到了一堆方法来取回列值:
╔══════════════╦═════════════════════╦════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════╗ ║ 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 ║ ╚══════════════╩═════════════════════╩════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════╝
Is the genernal expectation / practice to call:
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);
等等，对于所有的原始类型？由于其他一切都返回 null例如 SQL NULL .
如果是这样，当类型化对象方法存在时，拥有不同类型的所有方法有什么意义？
此外，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)并转换到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);
例如，我注意到 org.springframework.jdbc.core.JdbcTemplate 曾经有 , queryForLong 等方法，用于从单行查询中获取单个值并将它们全部替换为有利于类型化的 queryForInt queryForObject方法。
谢谢!
最佳答案
如果你看一下java.sql.ResultSet ，你可以看到你不需要那么明确。实际上，除非你有一个允许你使用 getObject 方法的连接类型映射器，否则它不会工作(java.sql.ResultSet.getObject)。
我不知道它是否对你有帮助，但我设法找到了一个我自己的 RowMapper，它非常适合我的需要。
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() );
}
}
我知道这是很多代码，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所有从行信息中提取对象的“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，您就永远不会遇到提取空行的问题。虽然我认为检查 ResultSet 的空响应不会有什么坏处，但如果该列应该有一个值，您仍然会最终抛出异常。
关于Java Spring - RowMapper ResultSet - 整数/空值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33266078/