synchronized Problem - variable return problem

[Nakata kokuyo]

hi, i have 2 methods , which use synchronized, and both methods share a variable as following template code :

 
private List list = new ArrayList();
 
public synchronized void setParamList(List _list)
{
    list = _list;
}
 
public synchronized List getParamList()
{
    return list;
}
 
public synchronized void simpleSQL()
{
    ... // sql query which use preparaStatement, with different ? for parameter, however, i avoid use setParameter(), so i use like following
 
   String _query ; 
 
   sqllist.add(param1);
   sqllist.add(param2);
   
   setParamList(sqlList);
    // the size of sqlList = 2
 
   resultList = generalQueryMethod(String _query)
 
}
 
public synchronized  List generalQueryMethod(String _query)
{
   List sqlParamList = getParamList();
   //sqlParamList size = 0
   
}
 

the problem here is when i set the list which in this case to size=2, but how come when i retrieve back the list using getParamList() and the size=0 ?

can anyone spot the problem , thanks for guidance

note :: i run this as utility class in my web application, which i start the method with simpleSQL() first then only generalQueryMethod()

[Ernest Friedman-Hill]

There's nothing wrong here, but you're obviously not showing the real code (the line

resultList = generalQueryMethod(String _query)

gives that away.) We can't find problems if we don't see the real code!

Nothing you've shown here involves multiple threads, so nothing requires these methods to be synchronized (of course, nothing requires "list" to be a member as opposed to a local, either, so again you're not showing us the whole picture.

[Nakata kokuyo]

sorry for unclear, here is my real sample code, it might too long to show here, that's why i just give a scenario, and i take out the exception part

 public synchronized List getDefaultSalesmanInfo(String dist_cd, String sortCol, boolean isSortedAsc)
            throws NpException {
 
        List sqlParamList = new ArrayList();
        List returnSqlList = new ArrayList();
 
        ResultSet rs = null;
 
        try {
 
            StringBuffer query = new StringBuffer();
            query.append("SELECT a.DIST_CD, a.SLSMAN_CD, b.SLSMAN_NAME FROM ")
                    .append(getDbSchema()).append(".O_DISTSLSMAN a, ")
                    .append(getDbSchema()).append(".O_SALESMAN b ")
                    .append("WHERE b.SYNCOPERATION <> 'D' ")
                    .append("AND a.SLSMAN_CD=b.SLSMAN_CD AND a.DIST_CD=? ");
 
            if (sortCol != null && !sortCol.equals(""))
                query.append(" ORDER BY ").append(getUpperStatement(sortCol));
            if (!isSortedAsc)
                query.append(" DESC");
 
            getLogger().log(NpLogger.DEBUG, "SalesmanController.getDistSalesman(). SQL="
                    + query + "|1=" + dist_cd);
 
 
             rs = getSqlResultSet(query.toString());
 
            sqlParamList.add(dist_cd);
            System.out.println("sqlParamList size in getDefault() ====" + sqlParamList.size());
            setSqlParam(sqlParamList);
 
            returnSqlList = getSqlResultList(rs); // call getSqlResultList(rs)
        }
        
        return returnSqlList;
    }

 public synchronized ResultSet getSqlResultSet(String _sql) throws NpException {
 
        Connection dbCon = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        ArrayList list = null;
        String sql = _sql;
        List sqlParamList = new ArrayList();
 
        try {
            dbCon = getConnection();
            dbCon.setAutoCommit(true);
 
            ps = dbCon.prepareStatement(sql);
            displayListSize();
            sqlParamList = getSqlParam();
            System.out.println("sqlParamList size ===" + sqlParamList.size());
            for (int i = 0; i < sqlParamList.size(); i++) {
                String sqlParamStr = (String) sqlParamList.get(i);
                ps.setString(i + 1, sqlParamStr);
                System.out.println("sqlParamStr ===" + sqlParamStr);
            }
 
            resultSet = ps.executeQuery();
 
        } 
 
        return resultSet;
    }
 

// set the parameter into list which use getSqlResultset()
    public synchronized void setSqlParam(List _sqlList) {
 
        if (_sqlList.size() > 0) {
            this.sqlList = _sqlList;
          
        }
    }

 public synchronized  List getSqlParam() {        
        return this.sqlList;
    }

[ November 09, 2005: Message edited by: Nakata kokuyo ]
[ November 09, 2005: Message edited by: Nakata kokuyo ]

[Ernest Friedman-Hill]

Maybe you're confused about where the code is going? There are a lot of variables and methods with similar names here, and maybe you're looking at the wrong ones. I know it's hard for me to find my way around. For example, you show the method

public synchronized ResultSet getSqlResultSet(String _sql) throws NpException

but it isn't called anywhere in your example code; you don't show

List getSqlResultList(ResultSet rs)

which is called from getDefaultSalesmanInfo(); in fact, it's the only thing called after setSqlParam(), so it's the only thing that would have a chance to report the problem you're seeing. Take a good look at getSqlResultList() and see if that doesn't clear things up...

[Nakata kokuyo]

getSqlResultList() code

 public synchronized List getSqlResultList(ResultSet _rs) {
        ResultSet rs = _rs;
        List tempResultList = new ArrayList();
        int count = 1;
        try {
            while (rs.next()) {
                Object tempObj = rs.getObject(count);
                tempResultList.add(tempObj);
                count ++;
            }
        } catch (SQLException e) {
            e.printStackTrace();  
        }
        return tempResultList;
    }

[Ernest Friedman-Hill]

OK, so now, in the call tree starting from getDefaultSalesmanInfo(), you're never calling getSqlParam(). So how do you know that the member sqlList is of length 0?

[Nakata kokuyo]

the getSqlParam() call from getSqlResultSet(), which is pass to another list

sqlParamList = getSqlParam();

[Ernest Friedman-Hill]

Right, but that's [before you call setSqlParam(). Of course the list is still empty at that point; you haven't set it to anything yet.

[Nakata kokuyo]

Ernest, you are right , i very disappointed with such stupid mistake,

anyway, when we use synchronized method, should we put all method as synchronized ?

for example, should i get rig on synchronized in getSqlResultSet() method? the reason i think on get rid it, is due to the getSqlResultSet() might share by other method..

say if getSqlResultSet() is a general method to execute query, it might call by other method as well , if i make it synchronized, would it affect other method which couldn't access it ?

lastly , thank you very much for your guidance and have a nice day