com.webcab.ejb.finance.trading.indicators.jdbc
Interface MovingAverageJDBC

All Superinterfaces:

EJBObject, Remote

public interface MovingAverageJDBC

extends EJBObject

A JDBC interface for the MovingAverage Enterprise JavaBean. This component consists of several business methods that apply MovingAverage methods onto SQL query results and SQL update queries directly from and into your DBMS.

This component is designed to easily transfer onto an Application Server JDBC specific tasks that make use of the mathematical capabilities of the MovingAverage enterprise Bean.

This component contains four methods:

• Two methods to retrieve JDBC queries and place the results back into your database
• A method to retrieve JDBC queries and return the results as Java objects
• A method to accept Java objects as parameters and place the results into your database

Every one of these four methods looks up the name of the method you wish to apply to your database entries and according to its parameters, decides where to read the input parameters from and where to write them back to.

Since every method accepts as parameter the name of the method contained by the MovingAverage bean and determines which one to use according to the number of columns the input query returns or the length of the parameter array, we can consider the following generic examples.

If you wish to invoke a bean's method the standard way by passing its parameters directly from your Java class and you require the resulting number to be written in a certain location in your database, you need to use the call (methodName, inputValues, outputQuery) method:

    // Create an EJB instance of this component
    JDBCInterface jdbc = jdbcHome.create (...)
    
    // Invoke a generic method from the MovingAverage bean
    jdbc.call ("myMethodName", new Double[]
               {new Double (6), new Double (0.8)},
               "INSERT INTO DATA3 (RESULT) VALUES (?)");
 

The previous call invokes method "myMethodName" from the MovingAverage bean which presumably accepts no more than two double parameters and using the prepared/callable statement

    INSERT INTO DATA3 (RESULT) VALUES (?)
 

adds a new row to the DATA3 table and writes the result computed by the "myMethodName" method in the RESULT field. As you may notice, the output query is a prepared/callable statement where the question mark has been replaced by the method "myMethodNames"'s result.

Say you need to take the input parameters from your database and retrieve the output as an array of Java objects, you will be using the following method:

    // Create an EJB instance of this component
    JDBCInterface jdbc = jdbcHome.create (...)

    // Invoke a generic method from the MovingAverage bean
    Object[] o = jdbc.call ("myMethodName", "SELECT * FROM FX_examples.GBP_USD_high");
    for (int i = 0; i < o.length; i++)
        System.out.println (o[i].toString ());
 

This call method retrieves the result set denoted by the SELECT statement, applies the method "myMethodName" from the MovingAverage bean to every row and puts the results in an array in the same order the rows were retrieved.

In order to read from a database and write back to a database, you will need to specify both an input and an output query. If the output location does not depend on the input location, you may use the call (methodName, inputQuery, outputQuery) method.

    // Create an EJB instance of this component
    JDBCInterface jdbc = jdbcHome.create (...)

    // Invoke a generic method from the MovingAverage bean
    jdbc.call ("myMethodName", "SELECT DATASET, WEIGHT FROM DATA",
                  "INSERT INTO DATA3 (RESULT ) VALUES (?)");
 

For every computed row using the "myMethodName" method from the MovingAverage bean, you add a new row to the DATA3 table in the RESULT field. Every question mark from the output query is replaced by the value of the result returned by "myMethodName". In case your method returns an array of values, every value is written into a corresponding question mark.

Please note that even though the results are written in the same order they were computed, the entries inserted in the DATA3 table do not point back to the entries in the input DATASET table.

Because of this limitation, we provide a more complex input/output query method which enables you to take full control over the way you update your database. In most input-output SQL queries you will require to somehow calculate the position of the computed result according to the position of the input values, taken from the same database. That is why this fourth method allows you to assign input query column values to certain question mark symbols contained by the output prepared/callable statement. This way you can control every output query to update table cells according to the value of a primary key or foreign key corresponding to the input values.

Please take a look at the following listing:

    // Create an EJB instance of this component
    JDBCInterface jdbc = jdbcHome.create (...)

    // Invoke a generic method from the MovingAverage bean
    jdbc.call ("myMethodName",
               "SELECT C_ID, SHARES, VALUE FROM TRADES",
               "UPDATE CUSTOMER SET MONEY=? WHERE C_ID=?",
               new int[][] {
                {2, 1}
               });
 

As you can see "myMethodName" is the method of choice from the MovingAverage bean and

    SELECT C_ID, SHARES, VALUE FROM TRADES
 

is the query to return the input values. The last parameter is an array of integer pairs, where the left item of every pair represents the number of the IN parameter (the question mark) of the prepared/callable statement and the right item points to the value from the input query result set to assign the IN parameter to. Both indices start numbering from 1. The input value is reassigned with every row to the corresponding IN parameter. In our case, we are assigning the second IN parameter (WHERE C_ID=?) to the first input column, C_ID.

Note that all input parameters assigned to at least one IN parameter will not be passed on to the method used to compute the input values. In this case only the fields SHARES and VALUE in the TRADES table will be considered. Of course if you require an assigned parameter to be computed as well, specify its name again in your SELECT statement.

Method Summary

void	call(String methodName, Serializable[] inputValues, String outputQuery) Given an array of Java objects, this method identifies the corresponding MovingAverage method methodName and writes the result of the computation to the database, as indicated by the output query.
Serializable[]	call(String methodName, String inputQuery) Given a SELECT type SQL query (retrieving rows from a database), this method identifies the corresponding MovingAverage method methodName and applies it to every row in the query result set returning the results in a Serializable[] array.
void	call(String methodName, String inputQuery, String outputQuery) Given a SELECT type SQL query (retrieving rows from a database), this method identifies the corresponding MovingAverage method methodName and applies it to every row in the query result set writing the results back to the database as specified by the output query.
void	call(String methodName, String inputQuery, String outputQuery, int[][] inputOutputPairs) Given a SELECT type SQL query (retrieving rows from a database), this method identifies the corresponding MovingAverage method methodName and applies it to every row in the query result set writing the results back to the database as specified by the output query and the input-output pairs.
MovingAverage	instance() This method returns the underlying EJB instance of the MovingAverage business class.
Serializable	oneSelect(String methodName, String inputQuery) Invokes method methodName once using values from running one SELECT statement.

Methods inherited from interface javax.ejb.EJBObject

getEJBHome, getHandle, getPrimaryKey, isIdentical, remove

Method Detail

instance

public MovingAverage instance()
                       throws RemoteException

This method returns the underlying EJB instance of the MovingAverage business class. Use this method to work directly with the MovingAverage EJB object.

RemoteException

oneSelect

public Serializable oneSelect(String methodName,
                              String inputQuery)
                       throws SQLException,
                              MovingAverageJDBCException,
                              RemoteException

Invokes method methodName once using values from running one SELECT statement. The parameters of the underlying method can be primitives (e.g. numbers), one-dimensional arrays, but at most one of them can be a two-dimensional array.

The inputQuery parameter of this method specifies the SELECT statement to use in invoking the underlying method. The columns of the result set returned by the SELECT statement correspond to the values of the parameters being sent to the underlying method as described below.

Calling Methods with Primitive Parameters

If methodName takes only non-array parameters, the method will be evaluated only for the first row in the SELECT result-set. The parameters will match their corresponding column in the same order -- first column value goes to the first parameter, second column value goes to the second parameter etc. The number of columns returned must be equal to or greater than the number of parameters in methodName's declaration.

Calling Methods with One-Dimensional Arrays and Primitive Parameters

If methodName takes both non-array and one-dimensional array parameters, the method will be evaluated only for the first row in the SELECT result-set for the non-array parameters, and for the entire column values for the one-dimensional array parameters. The parameters will match their corresponding column in the same order -- first column values go to the first parameter, second column values go to the second parameter etc. The number of columns returned must be equal to or greater than the number of parameters in methodName's declaration.

Calling Methods with a Two-Dimensional Array Parameter

If methodName takes (besides non-array and one-dimensional array parameters) one two-dimensional array parameter, the values being sent to the two-dimensional array parameter stretch between the last of the first columns (corresponding to the first primitive and/or array parameters) and the first of the last columns (corresponding to the last primitive and/or array parameters). In this case, this method will assume that all values returned by the SELECT statement are being used. Also note that every column represents a one-dimensional array element in the two-dimensional array value.

Consider the following example for a fictive underlying method with the following signature:

     double[][] bicubicSplinePointwiseEvaluation(
                            double[] tabulationPointsInFirstVariable
                            double[] tabulationPointsInSecondVariable,
                            double[][] function,
                            double interpolationPointFirstCoordinate,
                            double interpolationPointSecondCoordinate)
 

First two parameters will be assigned to the first two columns returned by the SELECT statement and the last two parameters will be assigned to the last two columns. The third parameter, which is a two-dimensional array will be assigned to the remaining columns.

If the underlying method's return type is void, this method will return null.

Returns:

The value returned by methodName as invoked using the values from the database, or null if the methodName's return type is void.

SQLException

MovingAverageJDBCException

RemoteException

call

public void call(String methodName,
                 String inputQuery,
                 String outputQuery)
          throws SQLException,
                 MovingAverageJDBCException,
                 RemoteException

Given a SELECT type SQL query (retrieving rows from a database), this method identifies the corresponding MovingAverage method methodName and applies it to every row in the query result set writing the results back to the database as specified by the output query.

If the bean contains more than one method with the same name, this method will make its choice according to the number of columns the query will return. Note that the type of every column is not taken into consideration, since the bean does not contain methods that have the same name and the same number of parameters.

Parameters:

methodName - The name of the MovingAverage method you wish to analyze.

inputQuery - The SQL query text that will retrieve the results you wish to apply the method methodName to.

outputQuery - A prepared/callable statement (containing question mark symbols) to specify the UPDATE/INSERT write-back procedure.

SQLException

MovingAverageJDBCException

RemoteException

call

public void call(String methodName,
                 String inputQuery,
                 String outputQuery,
                 int[][] inputOutputPairs)
          throws SQLException,
                 MovingAverageJDBCException,
                 RemoteException

Given a SELECT type SQL query (retrieving rows from a database), this method identifies the corresponding MovingAverage method methodName and applies it to every row in the query result set writing the results back to the database as specified by the output query and the input-output pairs.

If the bean contains more than one method with the same name, this method will make its choice according to the number of columns the query will return. Note that the column types are not taken into consideration, since the bean does not contain methods that have the same name and the same number of parameters.

Every pair specifies the index (starting from 1) of the prepared/callable statement IN parameter and the index (starting from 1) of the input query column to assign to. Every column assigned to at least one IN parameter is not used for evaluation.

Parameters:

methodName - The name of the MovingAverage method you wish to analyze.

inputQuery - The SQL query text that will retrieve the results you wish to apply the method methodName to.

outputQuery - A prepared/callable statement (containing question mark symbols) to specify the UPDATE/INSERT write-back procedure.

inputOutputPairs - A list of pairs that assign to certain IN parameters column values returned by the input query. If you leave this parameter null or empty, this method will behave similarly to call(methodName, inputQuery, outputQuery).

SQLException

MovingAverageJDBCException

RemoteException

call

public void call(String methodName,
                 Serializable[] inputValues,
                 String outputQuery)
          throws SQLException,
                 MovingAverageJDBCException,
                 RemoteException

Given an array of Java objects, this method identifies the corresponding MovingAverage method methodName and writes the result of the computation to the database, as indicated by the output query.

If the bean contains more than one method with the same name, this method will make its choice according to the length of the array of objects.

If the method returns an array of objects, every of its elements are assigned to the IN parameters of the prepared/callable statement.

Parameters:

methodName - The name of the MovingAverage method you wish to analyze.

inputValues - An array of objects representing input values for the methodName.

outputQuery - A prepared/callable statement with at least one IN parameter describing where in the database to put the computed result.

SQLException

MovingAverageJDBCException

RemoteException

call

public Serializable[] call(String methodName,
                           String inputQuery)
                    throws SQLException,
                           MovingAverageJDBCException,
                           RemoteException

Given a SELECT type SQL query (retrieving rows from a database), this method identifies the corresponding MovingAverage method methodName and applies it to every row in the query result set returning the results in a Serializable[] array.

If the bean contains more than one method with the same name, this method will make its choice according to the number of columns the query will return. Note that the type of every column is not taken into consideration, since the bean does not contain methods that have the same name and the same number of parameters.

Parameters:

methodName - The name of the MovingAverage method you wish to analyze.

inputQuery - The SQL query text that will retrieve the results you wish to apply the method methodName to.

Returns:

An array of results where every item represents the result of the method methodName applied to the corresponding row from the SQL query result-set.

SQLException

MovingAverageJDBCException

RemoteException