问题
I am using a simple app to aid learning database with Apache.Derby and working in Eclipse. The following code runs ok but conn.getMetaData() does not return anything meaningful regarding the table - colnameslist.size for example is 0. However I added meta.getDatabaseProductName() to see what happened and that returns 'Apache.Derby' so I guess there is some sort of connection.
The connection url is "jdbc:derby:C:/Users/RonLaptop/MyDB".
The string passed into getTableContents() is "MYENERGYAPP.ENERGYTABLE7".
As it does not error I am at a bit of a loss.
package com.energy;
import javax.swing.*;
import javax.swing.table.*;
import java.sql.*;
import java.util.*;
/** an immutable table model built from getting
metadata about a table in a jdbc database
*/
public class JDBCTableModel extends AbstractTableModel {
Object[][] contents;
String[] columnNames;
Class[] columnClasses;
public JDBCTableModel (Connection conn,
String string)
throws SQLException {
super();
getTableContents (conn, string);
}
protected void getTableContents (Connection conn,
String string)
throws SQLException {
// get metadata: what columns exist and what
// types (classes) are they?
DatabaseMetaData meta = conn.getMetaData();
String productName = meta.getDatabaseProductName();
String[] types = null;
System.out.println ("got meta = " + meta);
ResultSet results =
meta.getColumns (null, null, string, null) ;
System.out.println ("got column results");
ArrayList colNamesList = new ArrayList();
ArrayList colClassesList = new ArrayList();
while (results.next()) {
colNamesList.add (results.getString ("COLUMN_NAME"));
System.out.println ("name: " +
results.getString ("COLUMN_NAME"));
int dbType = results.getInt ("DATA_TYPE");
switch (dbType) {
case Types.INTEGER:
colClassesList.add (Integer.class); break;
case Types.FLOAT:
colClassesList.add (Float.class); break;
case Types.DOUBLE:
case Types.REAL:
colClassesList.add (Double.class); break;
case Types.DATE:
case Types.TIME:
case Types.TIMESTAMP:
colClassesList.add (java.sql.Date.class); break;
default:
colClassesList.add (String.class); break;
};
System.out.println ("type: " +
results.getInt ("DATA_TYPE"));
}
columnNames = new String [colNamesList.size()];
colNamesList.toArray (columnNames);
columnClasses = new Class [colClassesList.size()];
colClassesList.toArray (columnClasses);
// get all data from table and put into
// contents array
Statement statement =
conn.createStatement ();
results = statement.executeQuery ("SELECT * FROM " +
string);
ArrayList rowList = new ArrayList();
while (results.next()) {
ArrayList cellList = new ArrayList();
for (int i = 0; i<columnClasses.length; i++) {
Object cellValue = null;
if (columnClasses[i] == String.class)
cellValue = results.getString (columnNames[i]);
else if (columnClasses[i] == Integer.class)
cellValue = new Integer (
results.getInt (columnNames[i]));
else if (columnClasses[i] == Float.class)
cellValue = new Float (
results.getInt (columnNames[i]));
else if (columnClasses[i] == Double.class)
cellValue = new Double (
results.getDouble (columnNames[i]));
else if (columnClasses[i] == java.sql.Date.class)
cellValue = results.getDate (columnNames[i]);
else
System.out.println ("Can't assign " +
columnNames[i]);
cellList.add (cellValue);
}// for
Object[] cells = cellList.toArray();
rowList.add (cells);
} // while
// finally create contents two-dim array
contents = new Object[rowList.size()] [];
for (int i=0; i<contents.length; i++)
contents[i] = (Object []) rowList.get (i);
System.out.println ("Created model with " +
contents.length + " rows");
// close stuff
results.close();
statement.close();
}
// AbstractTableModel methods
public int getRowCount() {
return contents.length;
}
public int getColumnCount() {
if (contents.length == 0)
return 0;
else
return contents[0].length;
}
public Object getValueAt (int row, int column) {
return contents [row][column];
}
// overrides methods for which AbstractTableModel
// has trivial implementations
public Class getColumnClass (int col) {
return columnClasses [col];
}
public String getColumnName (int col) {
return columnNames [col];
}
}
回答1:
Try using just the name of the table; when I do this, I don't need to put the name of the 'app' level in front of the table name (i.e. just EVERYGYTABLE7). And make sure the table name has that capitalization; it is possible to create a table with a mixed-case name, and I think Derby is strict about that.
回答2:
I'm just quite unclear from your question. First, try if your table exists (ignoring case) as something like the one mentioned below.
ResultSet rs = null;
try
{
DatabaseMetaData meta = conn.getMetaData();
rs = meta.getTables(null, null, null, new String[] {"TABLE"});
while (rs.next())
{
String currentTableName = rs.getString("TABLE_NAME");
if (currentTableName.equalsIgnoreCase(tableName))
{
//...Your code goes here.
}
}
}
catch(SQLException e)
{
LOGGER.log(Level.SEVERE, e.getMessage(), e);
}
finally
{
DbUtils.closeQuietly(rs); // Apache Commons DbUtils
}
回答3:
In the string "MYENERGYAPP.ENERGYTABLE7", ""MYENERGYAPP" is the Schema Name, and "ENERGYTABLE7" is the Table Name.
It looks like you are passing the entire string into the "tableName" argument of the DatabaseMetaData.getColumns() call.
Try passing the Schema Name into the "schemaName" argument (the second argument to getColumns()), and pass the Table Name into the "tableName" argument (the third argument).
See http://docs.oracle.com/javase/1.4.2/docs/api/java/sql/DatabaseMetaData.html#getColumns(java.lang.String, java.lang.String, java.lang.String, java.lang.String)
来源：https://stackoverflow.com/questions/8770459/connection-getmetadata-does-not-seem-to-return-table-info