I'm using a ResultSet in Java, and am not sure how to properly close it. I'm considering using the ResultSet to construct a HashMap and then closing the ResultSet after that. Is this HashMap technique efficient, or are there more efficient ways of handling this situation? I need both keys and values, so using a HashMap seemed like a logical choice.
If using a HashMap is the most efficient method, how do I construct and use the HashMap in my code?
Here's what I've tried:
public HashMap resultSetToHashMap(ResultSet rs) throws SQLException {
ResultSetMetaData md = rs.getMetaData();
int columns = md.getColumnCount();
HashMap row = new HashMap();
while (rs.next()) {
for (int i = 1; i <= columns; i++) {
row.put(md.getColumnName(i), rs.getObject(i));
}
}
return row;
}
Iterate over the ResultSet
Create a new Object for each row, to store the fields you need
Add this new object to ArrayList or Hashmap or whatever you fancy
Close the ResultSet, Statement and the DB connection
Done
EDIT: now that you have posted code, I have made a few changes to it.
public List resultSetToArrayList(ResultSet rs) throws SQLException{
ResultSetMetaData md = rs.getMetaData();
int columns = md.getColumnCount();
ArrayList list = new ArrayList(50);
while (rs.next()){
HashMap row = new HashMap(columns);
for(int i=1; i<=columns; ++i){
row.put(md.getColumnName(i),rs.getObject(i));
}
list.add(row);
}
return list;
}
I just cleaned up RHT's answer to eliminate some warnings and thought I would share. Eclipse did most of the work:
public List<HashMap<String,Object>> convertResultSetToList(ResultSet rs) throws SQLException {
ResultSetMetaData md = rs.getMetaData();
int columns = md.getColumnCount();
List<HashMap<String,Object>> list = new ArrayList<HashMap<String,Object>>();
while (rs.next()) {
HashMap<String,Object> row = new HashMap<String, Object>(columns);
for(int i=1; i<=columns; ++i) {
row.put(md.getColumnName(i),rs.getObject(i));
}
list.add(row);
}
return list;
}
RHT pretty much has it. Or you could use a RowSetDynaClass and let someone else do all the work :)
this is my alternative solution, instead of a List of Map, i'm using a Map of List.
Tested on tables of 5000 elements, on a remote db, times are around 350ms for eiter method.
private Map<String, List<Object>> resultSetToArrayList(ResultSet rs) throws SQLException {
ResultSetMetaData md = rs.getMetaData();
int columns = md.getColumnCount();
Map<String, List<Object>> map = new HashMap<>(columns);
for (int i = 1; i <= columns; ++i) {
map.put(md.getColumnName(i), new ArrayList<>());
}
while (rs.next()) {
for (int i = 1; i <= columns; ++i) {
map.get(md.getColumnName(i)).add(rs.getObject(i));
}
}
return map;
}
A couple of things to enhance the other answers. First, you should never return a HashMap, which is a specific implementation. Return instead a plain old java.util.Map. But that's actually not right for this example, anyway. Your code only returns the last row of the ResultSet as a (Hash)Map. You instead want to return a List<Map<String,Object>>. Think about how you should modify your code to do that. (Or you could take Dave Newton's suggestion).
i improved the solutions of RHTs/Brad Ms and of Lestos answer.
i extended both solutions in leaving the state there, where it was found.
So i save the current ResultSet position and restore it after i created the maps.
The rs is the ResultSet, its a field variable and so in my solutions-snippets not visible.
I replaced the specific Map in Brad Ms solution to the gerneric Map.
public List<Map<String, Object>> resultAsListMap() throws SQLException
{
var md = rs.getMetaData();
var columns = md.getColumnCount();
var list = new ArrayList<Map<String, Object>>();
var currRowIndex = rs.getRow();
rs.beforeFirst();
while (rs.next())
{
HashMap<String, Object> row = new HashMap<String, Object>(columns);
for (int i = 1; i <= columns; ++i)
{
row.put(md.getColumnName(i), rs.getObject(i));
}
list.add(row);
}
rs.absolute(currRowIndex);
return list;
}
In Lestos solution, i optimized the code. In his code he have to lookup the Maps each iteration of that for-loop. I reduced that to only one array-acces each for-loop iteration. So the program must not seach each iteration step for that string-key.
public Map<String, List<Object>> resultAsMapList() throws SQLException
{
var md = rs.getMetaData();
var columns = md.getColumnCount();
var tmp = new ArrayList[columns];
var map = new HashMap<String, List<Object>>(columns);
var currRowIndex = rs.getRow();
rs.beforeFirst();
for (int i = 1; i <= columns; ++i)
{
tmp[i - 1] = new ArrayList<>();
map.put(md.getColumnName(i), tmp[i - 1]);
}
while (rs.next())
{
for (int i = 1; i <= columns; ++i)
{
tmp[i - 1].add(rs.getObject(i));
}
}
rs.absolute(currRowIndex);
return map;
}
Here is the code little modified that i got it from google -
List data_table = new ArrayList<>();
Class.forName("oracle.jdbc.driver.OracleDriver");
con = DriverManager.getConnection(conn_url, user_id, password);
Statement stmt = con.createStatement();
System.out.println("query_string: "+query_string);
ResultSet rs = stmt.executeQuery(query_string);
ResultSetMetaData rsmd = rs.getMetaData();
int row_count = 0;
while (rs.next()) {
HashMap<String, String> data_map = new HashMap<>();
if (row_count == 240001) {
break;
}
for (int i = 1; i <= rsmd.getColumnCount(); i++) {
data_map.put(rsmd.getColumnName(i), rs.getString(i));
}
data_table.add(data_map);
row_count = row_count + 1;
}
rs.close();
stmt.close();
con.close();
public static List<HashMap<Object, Object>> GetListOfDataFromResultSet(ResultSet rs) throws SQLException {
ResultSetMetaData metaData = rs.getMetaData();
int count = metaData.getColumnCount();
String[] columnName = new String[count];
List<HashMap<Object,Object>> lst=new ArrayList<>();
while(rs.next()) {
HashMap<Object,Object> map=new HashMap<>();
for (int i = 1; i <= count; i++){
columnName[i-1] = metaData.getColumnLabel(i);
map.put(columnName[i-1], rs.getObject(i));
}
lst.add(map);
}
return lst;
}
Related
So I'm trying to store a MySQL query result set into a multi dimensional HashMap as listed so:
public HashMap<String, HashMap<String, String>> getData(String query)
{
Statement stmt = null;
HashMap<String, HashMap<String, String>> results = new HashMap<String, HashMap<String, String>>();
try
{
stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(query);
ResultSetMetaData rsmd = rs.getMetaData();
while (rs.next())
{
for (int i = 1; i < rsmd.getColumnCount() + 1; i++)
{
results.put(Integer.toString(i - 1), new HashMap<String, String>());
results.get(Integer.toString(i - 1)).put(rsmd.getColumnLabel(i), rs.getString(i));
}
}
}
catch (SQLException ex)
{
ex.printStackTrace(System.out);
}
return results;
}
However when using the function to print it out as so:
public static void printMap(Map mp)
{
Iterator it = mp.entrySet().iterator();
while (it.hasNext())
{
Map.Entry pair = (Map.Entry)it.next();
System.out.println(pair.getKey() + " = " + pair.getValue());
it.remove();
}
}
It is only storing a single row result and I can't wrap my head around why.
0 = {Date=2014-11-04}
1 = {Num=1256}
2 = {ATime=null}
3 = {ALocCode=null}
4 = {DTime=1:00 PM}
5 = {DLocCode=JFK}
6 = {EstATime=8:00 PM}
7 = {EstDTime=1:00 PM}
8 = {EId=7624}
My question is, and the only way I can put it is relating to PHP, is how can I make it store like this?
$result[0]['Date'] = '3214';
....
$result[1]['Date'] = '6426';
Since that is essentially what I'm trying to achieve?
main problem that you've swapped "rows" and "columns", next one is that you're re-creating HashMap every time you put field, proper code will look like this:
public Map<String, Map<String, String>> getData(final String query) {
final Map<String, Map<String, String>> results = new HashMap<>();
try (final Statement stmt = this.conn.createStatement(); final ResultSet rs = stmt.executeQuery(query);) {
final ResultSetMetaData rsmd = rs.getMetaData();
long rId = 0;
while (rs.next()) {
final Map<String, String> record = new HashMap<>();
for (int i = 1; i < (rsmd.getColumnCount() + 1); i++) {
record.put(rsmd.getColumnLabel(i), rs.getString(i));
}
results.put(String.valueOf(rId++), record);
}
} catch (final SQLException ex) {
ex.printStackTrace(System.out);
}
return results;
}
public static void printMap(final Map<?, ?> mp) {
for (final Entry<?, ?> entry : mp.entrySet()) {
final Object key = entry.getKey();
final Object value = entry.getValue();
if (value instanceof Map) {
System.out.println(key);
printMap((Map<?, ?>) value);
} else {
System.out.println(key + "=" + entry.getValue());
}
}
}
The answer by Lashane is good for the errors you needed solving, however it can be improved:
You wanted numeric access ($result[0]['Date']) to the rows, not string.
print method should use fully typed parameter.
Rows should be stored in TreeMap or LinkedHashMap or ArrayList to retain row order. ArrayList is better for your case, actually.
Columns should be stored in LinkedHashMap to retain column order.
Do not catch exception and continue. Allow it to cascade up to caller.
Updated version:
public List<Map<String, String>> getData(final String query) throws SQLException {
final List<Map<String, String>> results = new ArrayList<>();
try (Statement stmt = this.conn.createStatement();
ResultSet rs = stmt.executeQuery(query)) {
ResultSetMetaData metaData = rs.getMetaData();
while (rs.next()) {
Map<String, String> record = new LinkedHashMap<>();
for (int col = 1; col <= metaData.getColumnCount(); col++)
record.put(metaData.getColumnLabel(col), rs.getString(col));
results.add(record);
}
}
return results;
}
public static void printMap(List<Map<String, String>> rows) {
for (int rowNum = 0; rowNum < rows.size(); rowNum++)
System.out.println(rowNum + " = " + rows.get(rowNum));
}
You can now access it like you did in PHP:
// PHP (for reference, the way you requested)
$result[0]['Date']
// Java
result.get(0).get("Date")
// Groovy
result[0]['Date']
result[0].Date
// JSP
<c:forEach var="row" items="${result}" varStatus="rowStatus">
${rowStatus.index} = <c:out value="${row.Date}"/>, ...
</c:forEach>
How can I get the value of HashTable inside the arrayList?
I have the following code:
public ArrayList resultSetToArrayList(ResultSet rs) {
ArrayList list = new ArrayList();
try {
ResultSetMetaData md = rs.getMetaData();
int columns = md.getColumnCount();
int rowcount = 0;
while (rs.next()) {
Hashtable row = new Hashtable();
for (int i = 1; i <= columns; ++i) {
row.put(md.getColumnName(i), rs.getString(i));
}
list.add(rowcount, row);
rowcount++;
}
} catch (Exception e) {
e.printStackTrace();
}
return list;
}
You appear to be using raw types and Hashtable instead of a HashMap. I think you're asking for something like
public List<Map<String, String>> resultSetToArrayList(ResultSet rs) {
List<Map<String, String>> list = new ArrayList<>();
try {
ResultSetMetaData md = rs.getMetaData();
int columns = md.getColumnCount();
while (rs.next()) {
Map<String, String> row = new HashMap<>();
for (int i = 1; i <= columns; ++i) {
row.put(md.getColumnName(i), rs.getString(i));
}
list.add(row);
}
} catch (Exception e) {
e.printStackTrace();
}
return list;
}
As for getting the values back out of a Map, you might iterate the Map.keySet() like
for (String key : map.keySet()) {
System.out.printf("%s = %s%n", key, map.get(key));
}
I would like to create DefaultTableModel from ResultSet. To do that, I need Object[][].
For that, I have to specify the size of the object before I iterate through the table: I go to the rs.last(), then rs.getRow(), then rs.beforeFirst();
After that, the rs.next() does not executes in the while cycle.
What am I doing wrong?
public static DefaultTableModel buildTableModel(ResultSet _resultSet) {
ResultSetMetaData metaData;
Object[] columnNames = null;
Object[][] tableData = null;
int columnCount;
int currentRowNumber = 0;
try {
metaData = _resultSet.getMetaData();
columnCount = metaData.getColumnCount();
columnNames = new Object[columnCount];
_resultSet.last();
tableData = new Object[_resultSet.getRow()][columnCount];
_resultSet.beforeFirst();
for (int currentColumn = 0; currentColumn <= columnCount; currentColumn++) {
columnNames[currentColumn] = metaData.getColumnName(currentColumn + 1);
}
while (_resultSet.next()) {
for (int columnIndex = 0; columnIndex <= columnCount; columnIndex++) {
tableData[currentRowNumber][columnIndex] = _resultSet.getObject(columnIndex + 1);
}
currentRowNumber++;
}
} catch (SQLException ex) {
System.out.println("bad");
}
return new DefaultTableModel(tableData, columnNames);
}
Probably your ResultSet is not scroll insensitive, that is, it can only be traversed forward.
See the documentation here:
[...] A default ResultSet object is not updatable and has a cursor that moves forward only. Thus, you can iterate through it only once and only from the first row to the last row. [...]
To create a bi-directional one, do something like:
Connection conn = DriverManager.getConnection(...);
Statement stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ...);
ResultSet rset = stmt.executeQuery(sql);
At first you need to print column name from ResultSetMetaData. Than you apply _resultSet.last(); and _resultSet.beforeFirst();. This way it has been working my machine.
public static DefaultTableModel buildTableModel(ResultSet _resultSet) {
ResultSetMetaData metaData;
Object[] columnNames = null;
Object[][] tableData = null;
int columnCount;
int currentRowNumber = 0;
try {
metaData = _resultSet.getMetaData();
columnCount = metaData.getColumnCount();
columnNames = new Object[columnCount];
// Print column here.
for (int currentColumn = 0; currentColumn <= columnCount; currentColumn++) {
columnNames[currentColumn] = metaData.getColumnName(currentColumn + 1);
}
tableData = new Object[_resultSet.getRow()][columnCount];
//Here point resultSet cursor to last and beforeFirst.
_resultSet.last();
_resultSet.beforeFirst();
// After swaping the above part. Now it will enter on while loop.
while (_resultSet.next()) {
for (int columnIndex = 0; columnIndex <= columnCount; columnIndex++) {
tableData[currentRowNumber][columnIndex] = _resultSet.getObject(columnIndex + 1);
}
currentRowNumber++;
}
} catch (SQLException ex) {
System.out.println("bad");
}
return new DefaultTableModel(tableData, columnNames);
}
Problem I have now is that the stored procedure called by the jdbcTemplate returns large amount of records, million records, which make our java query method very slow.
My java query method does the paging of the results so it is very slow. How can I improve this without altering the DB stored procedure. That is, to query for specific rows only so the java method would not have the burden of processing million records to do the paging.
public PageModel<Map<String, String>> query(String sql, final int offset, final int limit) throws ReportException {
try {
return jdbcTemplate.query(sql, new ResultSetExtractor<PageModel<Map<String, String>>>() {
#Override
public PageModel<Map<String, String>> extractData(ResultSet rs)
throws SQLException, DataAccessException {
long startTime = System.nanoTime();
PageModel<Map<String, String>> pageModel = new PageModel<Map<String,String>>();
List<Map<String, String>> list = new ArrayList<Map<String,String>>();
int rows = 0;
// skip rows
for (int i=0; i<offset&&rs.next(); i++) {
rows++;
}
// get rows
for (int i=0; i<limit&&rs.next(); i++) {
Map<String, String> map = new HashMap<String, String>();
ResultSetMetaData metadata = rs.getMetaData();
int count = metadata.getColumnCount();
for (int j=1; j<=count; j++) {
map.put(metadata.getColumnName(j), rs.getString(j));
}
list.add(map);
rows++;
}
// iterate remaining rows to get total rows
while (rs.next())
rows++;
pageModel.setOffset(offset);
pageModel.setLimit(limit);
pageModel.setData(list);
pageModel.setTotal(rows);
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println("Query took: " + duration);
return pageModel;
}
});
} catch (DataAccessException e) {
throw new ReportException(e);
}
}
How can I improve this without altering the DB stored procedure.
There is no any solution in your case, only altering SP
If is there any way to insert a resultset into jtable directly?
Bad idea.
You shouldn't be passing anything from the java.sql package out of your persistence tier.
You can certainly iterate over a ResultSet and load the contents into your DefaultTableModel. But I wouldn't recommend it.
Something like this:
public DefaultTableModel map(ResultSet resultSet) throws SQLException
{
DefaultTableModel defaultTableModel = new DefaultTableModel();
ResultSetMetaData meta = resultSet.getMetaData();
int numberOfColumns = meta.getColumnCount();
while (resultSet.next())
{
Object [] rowData = new Object[numberOfColumns];
for (int i = 0; i < rowData.length; ++i)
{
rowData[i] = resultSet.getObject(i+1);
}
defaultTableModel.addRow(rowData);
}
return defaultTableModel;
}