java - 基于列标签的 CachedRowSetImpl getString 抛出 "Invalid column name"

Question

当我执行以下代码时，一切都很好:

ResultSet rs = con.prepareStatement("SELECT r.UID AS R FROM r").executeQuery();
System.out.println(rs.getMetaData().getColumnLabel(1));
rs.next();
System.out.println(rs.getString("R"));

结果是:

R
23

但是当我执行以下代码时:

ResultSet rs = con.prepareStatement("SELECT r.UID AS R FROM r").executeQuery();
CachedRowSetImpl rslt = new CachedRowSetImpl();
rslt.populate(rs);
System.out.println(rslt.getMetaData().getColumnLabel(1));
rslt.next();
System.out.println(rslt.getString("R"));

结果是:

R
java.sql.SQLException: Invalid column name

为什么这里会抛出异常？

Answer 1

问题在于 CachedRowSet (com.sun.rowset.CachedRowSetImpl) 的引用实现包含一个错误:当您按名称检索列时，它会使用columnName，并且不是columnLabel，因此违背了使用 columnLabel 检索的 JDBC 规范的其余部分值(value)观。此错误导致无法通过 columnLabel 从行集中检索值。

Oracle 的错误是 http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7046875 ，但是(惊讶，惊讶)他们不让公众观看。

有两种可能的解决方法。一种是检查您的驱动程序是否提供了一个属性，以使 ResultSetMetaData.getColumnName(..) 方法返回 columnLabel 值，第二种解决方法是创建一个子类CachedRowSetImpl(不幸的是，这需要很多重写方法)。

以下版本是从此消息复制的:Re: Regression from 2.1.6

import java.math.BigDecimal;
import java.sql.Array;
import java.sql.Blob;
import java.sql.Clob;
import java.sql.Ref;
import java.sql.SQLException;
import java.util.Calendar;
import java.util.Collection;
import java.util.Hashtable;

import javax.sql.rowset.RowSetMetaDataImpl;

import com.sun.rowset.CachedRowSetImpl;

public class FixedCachedRowSetImpl extends CachedRowSetImpl {

    private static final long serialVersionUID = -9067504047398250113L;
    private RowSetMetaDataImpl RowSetMD;

    public FixedCachedRowSetImpl() throws SQLException {
        super();
    }

    public FixedCachedRowSetImpl(Hashtable env) throws SQLException {
        super(env);
    }

    private int getColIdxByName(String name) throws SQLException {
        RowSetMD = (RowSetMetaDataImpl) this.getMetaData();
        int cols = RowSetMD.getColumnCount();

        for (int i = 1; i <= cols; ++i) {
            String colName = RowSetMD.getColumnLabel(i);
            if (colName != null) if (name.equalsIgnoreCase(colName))
                return (i);
            else
                continue;
        }
        throw new SQLException(resBundle.handleGetObject("cachedrowsetimpl.invalcolnm").toString());
    }

    @Override
    public Collection<?> toCollection(String column) throws SQLException {
        return toCollection(getColIdxByName(column));
    }

    @Override
    public String getString(String columnName) throws SQLException {
        return getString(getColIdxByName(columnName));
    }

    @Override
    public boolean getBoolean(String columnName) throws SQLException {
        return getBoolean(getColIdxByName(columnName));
    }

    @Override
    public byte getByte(String columnName) throws SQLException {
        return getByte(getColIdxByName(columnName));
    }

    @Override
    public short getShort(String columnName) throws SQLException {
        return getShort(getColIdxByName(columnName));
    }

    @Override
    public int getInt(String columnName) throws SQLException {
        return getInt(getColIdxByName(columnName));
    }

    @Override
    public long getLong(String columnName) throws SQLException {
        return getLong(getColIdxByName(columnName));
    }

    @Override
    public float getFloat(String columnName) throws SQLException {
        return getFloat(getColIdxByName(columnName));
    }

    @Override
    public double getDouble(String columnName) throws SQLException {
        return getDouble(getColIdxByName(columnName));
    }

    @Override
    public BigDecimal getBigDecimal(String columnName, int scale) throws SQLException {
        return getBigDecimal(getColIdxByName(columnName), scale);
    }

    @Override
    public byte[] getBytes(String columnName) throws SQLException {
        return getBytes(getColIdxByName(columnName));
    }

    @Override
    public java.sql.Date getDate(String columnName) throws SQLException {
        return getDate(getColIdxByName(columnName));
    }

    @Override
    public java.sql.Time getTime(String columnName) throws SQLException {
        return getTime(getColIdxByName(columnName));
    }

    @Override
    public java.sql.Timestamp getTimestamp(String columnName) throws SQLException {
        return getTimestamp(getColIdxByName(columnName));
    }

    @Override
    public java.io.InputStream getAsciiStream(String columnName) throws SQLException {
        return getAsciiStream(getColIdxByName(columnName));

    }

    @Override
    public java.io.InputStream getUnicodeStream(String columnName) throws SQLException {
        return getUnicodeStream(getColIdxByName(columnName));
    }

    @Override
    public java.io.InputStream getBinaryStream(String columnName) throws SQLException {
        return getBinaryStream(getColIdxByName(columnName));
    }

    @Override
    public Object getObject(String columnName) throws SQLException {
        return getObject(getColIdxByName(columnName));
    }

    @Override
    public int findColumn(String columnName) throws SQLException {
        return getColIdxByName(columnName);
    }

    @Override
    public java.io.Reader getCharacterStream(String columnName) throws SQLException {
        return getCharacterStream(getColIdxByName(columnName));
    }

    @Override
    public BigDecimal getBigDecimal(String columnName) throws SQLException {
        return getBigDecimal(getColIdxByName(columnName));
    }

    @Override
    public boolean columnUpdated(String columnName) throws SQLException {
        return columnUpdated(getColIdxByName(columnName));
    }

    @Override
    public void updateNull(String columnName) throws SQLException {
        updateNull(getColIdxByName(columnName));
    }

    @Override
    public void updateBoolean(String columnName, boolean x) throws SQLException {
        updateBoolean(getColIdxByName(columnName), x);
    }

    @Override
    public void updateByte(String columnName, byte x) throws SQLException {
        updateByte(getColIdxByName(columnName), x);
    }

    @Override
    public void updateShort(String columnName, short x) throws SQLException {
        updateShort(getColIdxByName(columnName), x);
    }

    @Override
    public void updateInt(String columnName, int x) throws SQLException {
        updateInt(getColIdxByName(columnName), x);
    }

    @Override
    public void updateLong(String columnName, long x) throws SQLException {
        updateLong(getColIdxByName(columnName), x);
    }

    @Override
    public void updateFloat(String columnName, float x) throws SQLException {
        updateFloat(getColIdxByName(columnName), x);
    }

    @Override
    public void updateDouble(String columnName, double x) throws SQLException {
        updateDouble(getColIdxByName(columnName), x);
    }

    @Override
    public void updateBigDecimal(String columnName, BigDecimal x) throws SQLException {
        updateBigDecimal(getColIdxByName(columnName), x);
    }

    @Override
    public void updateString(String columnName, String x) throws SQLException {
        updateString(getColIdxByName(columnName), x);
    }

    @Override
    public void updateBytes(String columnName, byte x[]) throws SQLException {
        updateBytes(getColIdxByName(columnName), x);
    }

    @Override
    public void updateDate(String columnName, java.sql.Date x) throws SQLException {
        updateDate(getColIdxByName(columnName), x);
    }

    @Override
    public void updateTime(String columnName, java.sql.Time x) throws SQLException {
        updateTime(getColIdxByName(columnName), x);
    }

    @Override
    public void updateTimestamp(String columnName, java.sql.Timestamp x) throws SQLException {
        updateTimestamp(getColIdxByName(columnName), x);
    }

    @Override
    public void updateAsciiStream(String columnName, java.io.InputStream x, int length) throws SQLException {
        updateAsciiStream(getColIdxByName(columnName), x, length);
    }

    @Override
    public void updateBinaryStream(String columnName, java.io.InputStream x, int length) throws SQLException {
        updateBinaryStream(getColIdxByName(columnName), x, length);
    }

    @Override
    public void updateCharacterStream(String columnName, java.io.Reader reader, int length) throws SQLException {
        updateCharacterStream(getColIdxByName(columnName), reader, length);
    }

    @Override
    public void updateObject(String columnName, Object x, int scale) throws SQLException {
        updateObject(getColIdxByName(columnName), x, scale);
    }

    @Override
    public void updateObject(String columnName, Object x) throws SQLException {
        updateObject(getColIdxByName(columnName), x);
    }

    @Override
    public Object getObject(String columnName, java.util.Map<String, Class<?>> map) throws SQLException {
        return getObject(getColIdxByName(columnName), map);
    }

    @Override
    public Ref getRef(String colName) throws SQLException {
        return getRef(getColIdxByName(colName));
    }

    @Override
    public Blob getBlob(String colName) throws SQLException {
        return getBlob(getColIdxByName(colName));
    }

    @Override
    public Clob getClob(String colName) throws SQLException {
        return getClob(getColIdxByName(colName));
    }

    @Override
    public Array getArray(String colName) throws SQLException {
        return getArray(getColIdxByName(colName));
    }

    @Override
    public java.sql.Date getDate(String columnName, Calendar cal) throws SQLException {
        return getDate(getColIdxByName(columnName), cal);
    }

    @Override
    public java.sql.Time getTime(String columnName, Calendar cal) throws SQLException {
        return getTime(getColIdxByName(columnName), cal);
    }

    @Override
    public java.sql.Timestamp getTimestamp(String columnName, Calendar cal) throws SQLException {
        return getTimestamp(getColIdxByName(columnName), cal);
    }

    @Override
    public void updateRef(String columnName, java.sql.Ref ref) throws SQLException {
        updateRef(getColIdxByName(columnName), ref);
    }

    @Override
    public void updateClob(String columnName, Clob c) throws SQLException {
        updateClob(getColIdxByName(columnName), c);
    }

    @Override
    public void updateBlob(String columnName, Blob b) throws SQLException {
        updateBlob(getColIdxByName(columnName), b);
    }

    @Override
    public void updateArray(String columnName, Array a) throws SQLException {
        updateArray(getColIdxByName(columnName), a);
    }

    @Override
    public java.net.URL getURL(String columnName) throws SQLException {
        return getURL(getColIdxByName(columnName));
    }
}

您还可以查看org.springframework.jdbc.support.rowset.ResultSetWrappingSqlRowSet ，其中还说:

Note: Since JDBC 4.0, it has been clarified that any methods using a String to identify the column should be using the column label. The column label is assigned using the ALIAS keyword in the SQL query string. When the query doesn't use an ALIAS, the default label is the column name. Most JDBC ResultSet implementations follow this new pattern but there are exceptions such as the com.sun.rowset.CachedRowSetImpl class which only uses the column name, ignoring any column labels. As of Spring 3.0.5, ResultSetWrappingSqlRowSet will translate column labels to the correct column index to provide better support for the com.sun.rowset.CachedRowSetImpl which is the default implementation used by JdbcTemplate when working with RowSets.