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annotate src/main/java/nl/cwi/monetdb/jdbc/MonetWrapper.java @ 295:003ae6d881db

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Add "final" keyword to method arguments and local variables where possible. It discovered some bugs in the MonetStatement constructor (changed the argument instead of object variable) which are fixed now. See also https://en.wikipedia.org/wiki/Final_(Java)
author Martin van Dinther <martin.van.dinther@monetdbsolutions.com>
date Thu, 01 Aug 2019 20:18:43 +0200 (2019-08-01)
parents 2d62ca1f758b
children 54137aeb1f92
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1 /*
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2 * This Source Code Form is subject to the terms of the Mozilla Public
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3 * License, v. 2.0. If a copy of the MPL was not distributed with this
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4 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
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5 *
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d4baf8a4b43a Update Copyright year to 2019
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6 * Copyright 1997 - July 2008 CWI, August 2008 - 2019 MonetDB B.V.
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7 */
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8
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9 package nl.cwi.monetdb.jdbc;
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11 import java.sql.SQLException;
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12 import java.sql.SQLFeatureNotSupportedException;
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14 /**
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15 * A Wrapper class which provide the ability to retrieve the delegate instance
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16 * when the instance in question is in fact a proxy class.
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17 *
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18 * The wrapper pattern is employed by many JDBC driver implementations to provide
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19 * extensions beyond the traditional JDBC API that are specific to a data source.
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20 * Developers may wish to gain access to these resources that are wrapped (the delegates)
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21 * as proxy class instances representing the the actual resources.
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22 * This class contains a standard mechanism to access these wrapped resources
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23 * represented by their proxy, to permit direct access to the resource delegates.
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24 *
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25 * @author Fabian Groffen, Martin van Dinther
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26 * @version 1.1
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27 */
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28 public class MonetWrapper implements java.sql.Wrapper {
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29 /**
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30 * Returns true if this either implements the interface argument or
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31 * is directly or indirectly a wrapper for an object that does.
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32 * Returns false otherwise. If this implements the interface then
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33 * return true, else if this is a wrapper then return the result of
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34 * recursively calling <code>isWrapperFor</code> on the wrapped object.
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35 * If this does not implement the interface and is not a wrapper, return
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36 * false. This method should be implemented as a low-cost operation
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37 * compared to <code>unwrap</code> so that callers can use this method to avoid
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38 * expensive <code>unwrap</code> calls that may fail.
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39 * If this method returns true then calling <code>unwrap</code> with the same argument should succeed.
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40 *
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41 * @param iface a Class defining an interface.
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42 * @return true if this implements the interface or directly or indirectly wraps an object that does.
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43 * @throws SQLException if an error occurs while determining whether this is a wrapper
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44 * for an object with the given interface.
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45 * @since 1.6
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46 */
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47 @Override
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48 public boolean isWrapperFor(final Class<?> iface) throws SQLException {
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49 return iface != null && iface.isAssignableFrom(getClass());
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50 }
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52 /**
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53 * Returns an object that implements the given interface to allow
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54 * access to non-standard methods, or standard methods not exposed by the proxy.
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55 * The result may be either the object found to implement the interface
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56 * or a proxy for that object.
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57 * If the receiver implements the interface then the result is the receiver
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58 * or a proxy for the receiver.
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59 * If the receiver is a wrapper and the wrapped object implements the interface
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60 * then the result is the wrapped object or a proxy for the wrapped object.
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61 * Otherwise return the result of calling <code>unwrap</code> recursively on
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62 * the wrapped object or a proxy for that result.
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63 * If the receiver is not a wrapper and does not implement the interface,
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64 * then an <code>SQLException</code> is thrown.
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65 *
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66 * @param iface A Class defining an interface that the result must implement.
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67 * @return an object that implements the interface. May be a proxy for the actual implementing object.
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68 * @throws SQLException If no object found that implements the interface
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69 * @since 1.6
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70 */
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71 @Override
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72 @SuppressWarnings("unchecked")
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73 public <T> T unwrap(final Class<T> iface) throws SQLException {
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74 if (isWrapperFor(iface)) {
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75 return (T) this;
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76 }
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77 throw new SQLException("Cannot unwrap to interface: " + (iface != null ? iface.getName() : ""), "0A000");
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78 }
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80 /**
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81 * Small helper method that formats the "Method ... not implemented" message
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82 * and creates a new SQLFeatureNotSupportedException object
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83 * whose SQLState is set to "0A000": feature not supported.
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84 *
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85 * @param name the method name
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86 * @return a new created SQLFeatureNotSupportedException object with SQLState 0A000
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87 */
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88 static final SQLFeatureNotSupportedException newSQLFeatureNotSupportedException(final String name) {
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89 return new SQLFeatureNotSupportedException("Method " + name + " not implemented", "0A000");
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90 }
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91 }