Groovy DAO Variable Scope Issue - grails

Question

In our Grails project we use a common Groovy DAO accessing an Amazon Oracle Database with PooledDataSource, and things were not working, and I suspect it was because the scope of some of the variables was incorrect. I have trimmed the code down and changed the names to a small subset of what we are doing in several locations. Some of the code in question was written by another developer with much more Java experience than me - I am a relative Java/Groovy novice - forgive the basic questions.
class SomeDAO {
MyPooledDataSource ds = new MyPooledDataSource()
Connection conn
PreparedStatement stmt
String queryText
public String getUserCount() {
String jsonOne
PojoOne one = new PojoOne()
ds.setDataSource()
conn = ds.getPooled()
queryText = getQuery("SomeQuery")
try {
stmt = conn.prepareStatement(queryText)
stmt.setString(1, 'YTD')
stmt.setString(2, '2014')
ResultSet rs = stmt.executeQuery()
while (rs.next()) {
one.setUsers(rs.getString("USER_CT"))
one.setDropped(rs.getString("DROPPED_CT"))
}
} catch (SQLException e) {}
jsonOne = (one as JSON).toString()
return jsonOne
}
public String getUserMetrics() {
String jsonTwo
ArrayList objArray = new ArrayList()
ds.setDataSource()
conn = ds.getPooled()
try {
queryText = getQuery("SomeOtherQuery")
stmt = conn.prepareStatement(queryText)
stmt.setString(1, 'YTD')
stmt.setString(2, '2014')
ResultSet rsQuery = stmt.executeQuery()
while (rsQuery.next()) {
PojoTwo two = new PojoTwo()
two.setDisplay(rsQuery.getString("NAME"))
two.setDescription(rsQuery.getString("DESC"))
two.setValue(rsQuery.getString("AMT"))
objArray.add(two)
}
} catch (SQLException e) {}
jsonTwo = (objArray as JSON).toString()
return jsonTwo
}
public String getQuery(String operationName){
String query = "select QRY_TXT from T_SVC_QRY where OPERATION_NM = '" + operationName + "'"
ResultSet rs
ds.setDataSource()
conn = ds.getPooled()
stmt = conn.prepareStatement(query)
rs = stmt.executeQuery(query)
while (rs.next()) {
queryText = rs.getString("QRY_TXT")
}
return queryText
}
}
I have a some concerns about the code we've written...
Seems like...
Connection conn
PreparedStatement stmt
String queryText
...should not be at the Class level, but declared in each method to avoid mutation of the variables by another method (or even the same method by a different request) causing side effects. Correct? Please explain
Should PooledDataSource be declared at the Class level for re-use. Correct? Please explain
Do we need to do the ds.setDataSource() in each method, or should that be done once for the class and why?
Seems like if try/catch is appropriate for the getUserCount and getUserMetrics methods, than it should be used in the getQuery method as well. Correct? Please explain

Answer 1

That's funky code. Only the DataSource should be shared. Do a Google search with your favorite search engine for groovy.sql.Sql - it's your best bet for working directly with JDBC in a Groovy or Grails project. It has lots of helper methods that let you write intuitive code and let it do the heavy lifting.
You might want to start by checking out the Javadoc page for the class.