function.java

一个用java写的开源的数据库系统

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 * Originally developed by Thomas Mueller and the Hypersonic SQL Group. 
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package org.hsqldb;

import java.sql.SQLException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Hashtable;

/**
 * Provides services to evaluate Java methods in the context of
 * SQL function and stored procedure calls.
 *
 * @version 1.7.0
 */

// fredt@users 20020912 - patch 1.7.1 - shortcut treatment of identity() call
// fredt@users 20020912 - patch 1.7.1 - cache java.lang.reflect.Method objects
// fredt@users 20021013 - patch 1.7.1 - ignore non-static methods
class Function {

    private Session          cSession;
    private String           sFunction;
    private Method           mMethod;
    private int              iReturnType;
    private int              iArgCount;
    private int              iArgType[];
    private boolean          bArgNullable[];
    private Object           oArg[];
    private Expression       eArg[];
    private boolean          bConnection;
    private boolean          isIdentityFunction;
    private static Hashtable methodCache = new Hashtable();

    /**
     * Constructs a new Function object with the given function call name
     * and using the specified Session context. <p>
     *
     * The call name is the fully qualified name of a static Java method, as
     * opposed to the method's canonical signature.  That is, the name
     * is of the form "package.class.method."  This implies that Java
     * methods with the same fully qualified name but different signatures
     * cannot be used properly as HSQLDB SQL functions or stored procedures.
     * For instance, it is impossible to call both System.getProperty(String)
     * and System.getProperty(String,String) under this arrangement, because
     * the HSQLDB Function object is unable to differentiate between the two;
     * it simply chooses the first method matching the FQN in the array of
     * methods obtained from calling getMethods() on an instance of the
     * Class indicated in the FQN, hiding all other methods with the same
     * FQN. <p>
     *
     * The function FQN must match at least one static Java method FQN in the
     * specified class or construction cannot procede and a SQLException is
     * thrown. <p>
     *
     * The Session paramter is the connected context in which this
     * Function object will evaluate.  If it is determined that the
     * connected user does not have the right to evaluate this Function,
     * construction cannot proceed and a SQLException is thrown.
     *
     *
     * @param function the fully qualified name of a Java method
     * @param session the connected context in which this Function object will
     *                evaluate
     * @throws SQLException if the specified function FQN corresponds to no
     *                      Java method or the session user at the time of
     *                      construction does not have the right to evaluate
     *                      this Function.
     */
    Function(String function, Session session) throws SQLException {

        cSession  = session;
        sFunction = function;

        if (function.equals("org.hsqldb.Library.identity")) {
            isIdentityFunction = true;
        }

        int i = function.lastIndexOf('.');

        Trace.check(i != -1, Trace.UNEXPECTED_TOKEN, function);

        String classname = function.substring(0, i);

        session.check("CLASS \"" + classname + "\"", UserManager.ALL);

        mMethod = (Method) methodCache.get(function);

        if (mMethod == null) {
            String methodname    = function.substring(i + 1);
            Class  classinstance = null;

            try {
                classinstance = Class.forName(classname);
            } catch (Exception e) {
                throw Trace.error(Trace.ERROR_IN_FUNCTION,
                                  classname + " " + e);
            }

            Method method[] = classinstance.getMethods();

            for (i = 0; i < method.length; i++) {
                Method m = method[i];

                if (m.getName().equals(methodname)
                        && Modifier.isStatic(m.getModifiers())) {
                    mMethod = m;

                    break;
                }
            }

            Trace.check(mMethod != null, Trace.UNKNOWN_FUNCTION, methodname);
            methodCache.put(function, mMethod);
        }

        Class returnclass = mMethod.getReturnType();

        iReturnType = Column.getTypeNr(returnclass.getName());

        Class arg[] = mMethod.getParameterTypes();

        iArgCount    = arg.length;
        iArgType     = new int[iArgCount];
        bArgNullable = new boolean[iArgCount];

        for (i = 0; i < arg.length; i++) {
            Class  a    = arg[i];
            String type = a.getName();

            if ((i == 0) && type.equals("java.sql.Connection")) {

                // only the first parameter can be a Connection
                bConnection = true;
            } else {

// fredt@users - byte[] is now supported directly as "[B"
//                if (type.equals("[B")) {
//                    type = "byte[]";
//                }
                iArgType[i]     = Column.getTypeNr(type);
                bArgNullable[i] = !a.isPrimitive();
            }
        }

        eArg = new Expression[iArgCount];
        oArg = new Object[iArgCount];
    }

    /**
     * Retrieves the value this Function evaluates to, given the current
     * state of this object's {@link #resolve(TableFilter) resolved}
     * TableFilter, if any, and any mapping of expressions to this
     * Function's parameter list that has been performed via
     * {link #setArgument(int,Expression) setArgument}.
     *
     *
     * @return the value resulting from evaluating this Function
     * @throws SQLException if an invocation exception is encountered when
     * calling the Java
     * method underlying this object
     */
    Object getValue() throws SQLException {

        int i = 0;

        if (isIdentityFunction) {
            return new Integer(cSession.getLastIdentity());
        }

        if (bConnection) {
            oArg[i] = cSession.getInternalConnection();

            i++;
        }

        for (; i < iArgCount; i++) {
            Expression e = eArg[i];
            Object     o = null;

            if (e != null) {

                // no argument: null
                o = e.getValue(iArgType[i]);
            }

            if ((o == null) &&!bArgNullable[i]) {

                // null argument for primitive datatype: don't call
                return null;
            }

            oArg[i] = o;
        }

        try {
            return mMethod.invoke(null, oArg);
        } catch (Exception e) {
            String s = sFunction + ": " + e.toString();

            throw Trace.getError(Trace.FUNCTION_NOT_SUPPORTED, s);
        }
    }

    /**
     * Retrieves the number of parameters that must be supplied to evaluate
     * this Function object from SQL.  <p>
     *
     * This value may be different than the number of parameters of the
     * underlying Java method.  This is because HSQLDB automatically detects
     * if the first parameter is of type java.sql.Connection, and supplies a
     * live Connection object constructed from the evaluating session context
     * if so.
     *
     *
     * @return the number of arguments this Function takes, as known to the
     * calling SQL context
     */
    int getArgCount() {
        return iArgCount - (bConnection ? 1
                                        : 0);
    }

    /**
     * Resolves the arguments supplied to this Function object against the
     * specified TableFilter.
     *
     *
     * @param f the TableFilter against which to resolve this Function
     * object's arguments
     * @throws SQLException if there is a problem resolving an argument
     * against the specified TableFilter
     */
    void resolve(TableFilter f) throws SQLException {

        for (int i = 0; i < iArgCount; i++) {
            if (eArg[i] != null) {
                eArg[i].resolve(f);
            }
        }
    }

    /**
     * Checks each of this object's arguments for resolution, throwing a
     * SQLException if any arguments have not yet been resolved.
     *
     *
     * @throws SQLException if any arguments have not yet been resolved
     */
    void checkResolved() throws SQLException {

        for (int i = 0; i < iArgCount; i++) {
            if (eArg[i] != null) {
                eArg[i].checkResolved();
            }
        }
    }

    /**
     * Retrieves the java.sql.Types type of the argument at the specified
     * offset in this Function object's paramter list
     *
     *
     * @param i the offset of the desired argument in this Function object's
     * paramter list
     * @return the specified argument's java.sql.Types type
     */
    int getArgType(int i) {
        return iArgType[i];
    }

    /**
     * Retrieves the java.sql.Types type of this Function
     * object's return type
     *
     *
     * @return this Function object's java.sql.Types return type
     */
    int getReturnType() {
        return iReturnType;
    }

    /**
     * Binds the specified expression to the specified argument in this
     * Function object's paramter list.
     *
     *
     * @param i the position of the agument to bind to
     * @param e the expression to bind
     */
    void setArgument(int i, Expression e) {

        if (bConnection) {
            i++;
        }

        eArg[i] = e;
    }
}