Merge pull request #11 from djunglas/master

Minor code improvements (reading scalar and exception safety)

Author: vlkong

lib/jdbc-custom-data-source.jar

@@ -215,7 +215,7 @@ public void readXML(InputStream input) throws IOException {
 
             // input parameters
             Node readNode = doc.getElementsByTagName(READ).item(0);
-            if (readNode.getNodeType() == Node.ELEMENT_NODE) {
+            if (readNode != null && readNode.getNodeType() == Node.ELEMENT_NODE) {
                 NodeList queries = ((Element)readNode).getElementsByTagName(QUERY);
                 for (int iquery = 0; iquery < queries.getLength(); iquery++) {
                     Node qNode = queries.item(iquery);
@@ -230,7 +230,7 @@ public void readXML(InputStream input) throws IOException {
 
             // write parameters
             Node writeNode = doc.getElementsByTagName(WRITE).item(0);
-            if (writeNode.getNodeType() == Node.ELEMENT_NODE) {
+            if (writeNode != null && writeNode.getNodeType() == Node.ELEMENT_NODE) {
                 NodeList tables = ((Element)writeNode).getElementsByTagName(TABLE);
                 for (int itable = 0; itable < tables.getLength(); itable++) {
                     Node tNode = tables.item(itable);
@@ -246,4 +246,4 @@ public void readXML(InputStream input) throws IOException {
             throw new RuntimeException("Could not read XML configuration");
         }
     }
-}
+}

src/main/java/com/ibm/opl/customdatasource/JdbcConfiguration.java

@@ -112,22 +112,33 @@ void fillNamesAndTypes(IloTupleSchema schema, String[] names, Type[] types) {
      * Overrides the IloCustomOplDataSource method to read data when the model
      * is generated.
      */
+    @Override
     public void customRead() {
         long startTime = System.currentTimeMillis();
-        System.out.println("Reading elements from database");
-        Properties prop = _configuration.getReadQueries();
-        Enumeration<?> propertyNames = prop.propertyNames();
-        while (propertyNames.hasMoreElements()) {
-            String name = (String) propertyNames.nextElement();
-            String query = prop.getProperty(name);
-            System.out.println("Reading " + name + " using \"" + query + "\"");
-            customRead(name, query);
+        try {
+            System.out.println("Reading elements from database");
+            Properties prop = _configuration.getReadQueries();
+            Enumeration<?> propertyNames = prop.propertyNames();
+            while (propertyNames.hasMoreElements()) {
+               String name = (String) propertyNames.nextElement();
+               String query = prop.getProperty(name);
+               System.out.println("Reading " + name + " using \"" + query + "\"");
+               customRead(name, query);
+            }
+            long endTime = System.currentTimeMillis();
+            System.out.println("Done (" + (endTime - startTime)/1000.0 + " s)");
+        }
+        catch (SQLException e) {
+            // Since the superclass's method signature does not allow us to
+            // throw an exception from here, we have to wrap the exception.
+            long endTime = System.currentTimeMillis();
+            System.err.println(e.getMessage() + " (after " + (endTime - startTime)/1000.0 + " s)");
+            e.printStackTrace();
+            throw new RuntimeException(e);
         }
-        long endTime = System.currentTimeMillis();
-        System.out.println("Done (" + (endTime - startTime)/1000.0 + " s)");
     }
 
-    public void customRead(String name, String query) {
+    public void customRead(String name, String query) throws SQLException {
         IloOplElementDefinition def = _def.getElementDefinition(name);
         Type type = def.getElementDefinitionType();
         Type leaf = def.getLeaf().getElementDefinitionType();
@@ -139,17 +150,105 @@ public void customRead(String name, String query) {
                 readSet(leaf, name, query);
             }
         }
+        else if ( type == Type.INTEGER || type == Type.FLOAT || type == Type.STRING ) {
+           readValue(name, query);
+        }
+        else
+           throw new IllegalArgumentException("Cannot read element " + name + " of type " + type);
     }
 
-    public void readSet(Type leaf, String name, String query) {
+    /** Helper class to execute queries in an exception safe way.
+     * Use the class via the following template:
+     * <pre>
+     final RunQuery q = new RunQuery("SELECT * FROM table;");
+     try {
+        ResultSet rs = q.getResult();
+        ...
+     }
+     finally {
+        q.close();
+     }
+     </pre>
+     * This will correctly clean up and release all resources no matter whether
+     * an exception is throw or not.
+     */
+    private final class RunQuery {
+       private Connection conn = null;
+       private Statement stmt = null;
+       private ResultSet rs = null;
+       public RunQuery(String query) throws SQLException {
+          Connection conn = DriverManager.getConnection(_configuration.getUrl(),
+                                                        _configuration.getUser(),
+                                                        _configuration.getPassword());
+          Statement stmt = null;
+          ResultSet rs = null;
+          try {
+             stmt = conn.createStatement();
+             rs = stmt.executeQuery(query);
+             // Everything worked without problem. Transfer ownership of
+             // the objects to the newly constructed instance.
+             this.conn = conn; conn = null;
+             this.stmt = stmt; stmt = null;
+             this.rs = rs; rs = null;
+          }
+          finally {
+             if ( rs != null )  rs.close();
+             if ( stmt != null )  stmt.close();
+             if ( conn != null )  conn.close();
+          }
+       }
+       public void close() throws SQLException {
+          rs.close();
+          stmt.close();
+          conn.close();
+       }
+       ResultSet getResult() { return rs; }
+    }
+
+    /** Read the scalar value for <code>name</code> from <code>query</code>.
+     * <b>Note:</b> the function will just use the first value produced by
+     *              <code>query</code> and assign that to the element identified
+     *              by <code>name</code>. If the query produces more than one
+     *              value the surplus values are ignored.
+     * @param name The name of the element to fill.
+     * @param query The SQL query that produces the data for <code>name</code>.
+     * @throws SQLException if querying the database fails or the query does
+     *                      not produce at least one value.
+     */
+    public void readValue(String name, String query) throws SQLException {
+        IloOplElementDefinition def = _def.getElementDefinition(name);
         IloOplDataHandler handler = getDataHandler();
+        final RunQuery q = new RunQuery(query);
         try {
-            Connection conn = DriverManager.getConnection(_configuration.getUrl(),
-                    _configuration.getUser(),
-                    _configuration.getPassword());
-            Statement stmt = conn.createStatement();
-            ResultSet rs = stmt.executeQuery(query);
+           ResultSet rs = q.getResult();
+           rs.next();
+           handler.startElement(name);
+           Type type = def.getElementDefinitionType();
+           if (type == Type.INTEGER) {
+               handler.addIntItem(rs.getInt(1));
+           }
+           else if (type == Type.FLOAT) {
+               handler.addNumItem(rs.getDouble(1));
+           }
+           else if (type == Type.STRING) {
+               handler.addStringItem(rs.getString(1));
+           }
+           else
+              throw new IllegalArgumentException("Cannot load element " + name + " of type " + type);
+           handler.endElement();
+        }
+        finally {
+            // We don't use try-with-resources so that we can compile
+            // with pre-1.8 compilers as well.
+            q.close();
+        }
+    }
 
+    public void readSet(Type leaf, String name, String query) throws SQLException {
+        IloOplDataHandler handler = getDataHandler();
+        final RunQuery q = new RunQuery(query);
+        try {
+            ResultSet rs = q.getResult();
             handler.startElement(name);
             handler.startSet();
 
@@ -163,32 +262,27 @@ else if (leaf == Type.STRING)
             }
             handler.endSet();
             handler.endElement();
-            rs.close();
-            stmt.close();
-            conn.close();
-        } catch (SQLException e) {
-            e.printStackTrace();
+        }
+        finally {
+            q.close();
         }
     }
 
-    public void readTupleSet(String name, String query) {
+    public void readTupleSet(String name, String query) throws SQLException {
         IloOplDataHandler handler = getDataHandler();
-        try {
-            IloOplElement elt = handler.getElement(name);
-            ilog.opl_core.cppimpl.IloTupleSet tupleSet = (ilog.opl_core.cppimpl.IloTupleSet) elt.asTupleSet();
-            IloTupleSchema schema = tupleSet.getSchema_cpp();
-            int size = schema.getTotalColumnNumber();
+        IloOplElement elt = handler.getElement(name);
+        ilog.opl_core.cppimpl.IloTupleSet tupleSet = (ilog.opl_core.cppimpl.IloTupleSet) elt.asTupleSet();
+        IloTupleSchema schema = tupleSet.getSchema_cpp();
+        int size = schema.getTotalColumnNumber();
 
-            String[] oplFieldsName = new String[size];
-            Type[] oplFieldsType = new Type[size];
+        String[] oplFieldsName = new String[size];
+        Type[] oplFieldsType = new Type[size];
 
-            fillNamesAndTypes(schema, oplFieldsName, oplFieldsType);
+        fillNamesAndTypes(schema, oplFieldsName, oplFieldsType);
 
-            Connection conn = DriverManager.getConnection(_configuration.getUrl(),
-                    _configuration.getUser(),
-                    _configuration.getPassword());
-            Statement stmt = conn.createStatement();
-            ResultSet rs = stmt.executeQuery(query);
+        final RunQuery q = new RunQuery(query);
+        try {
+            ResultSet rs = q.getResult();
 
             handler.startElement(name);
             handler.startSet();
@@ -208,12 +302,9 @@ public void readTupleSet(String name, String query) {
             }
             handler.endSet();
             handler.endElement();
-            rs.close();
-            stmt.close();
-            conn.close();
-        } catch (SQLException e) {
-            e.printStackTrace();
         }
-
+        finally {
+            q.close();
+        }
     }
 };