The basic service for managing a set of JDBC drivers.
NOTE: The DataSource
interface, new in the
JDBC 2.0 API, provides another way to connect to a data source.
The use of a DataSource
object is the preferred means of
connecting to a data source.
As part of its initialization, the DriverManager
class will
attempt to load the driver classes referenced in the "jdbc.drivers"
system property. This allows a user to customize the JDBC Drivers
used by their applications. For example in your
~/.hotjava/properties file you might specify:
jdbc.drivers=foo.bah.Driver:wombat.sql.Driver:bad.taste.ourDriver
A program can also explicitly load JDBC drivers at any time. For
example, the my.sql.Driver is loaded with the following statement:
Class.forName("my.sql.Driver");
When the method getConnection
is called,
the DriverManager
will attempt to
locate a suitable driver from amongst those loaded at
initialization and those loaded explicitly using the same classloader
as the current applet or application.
Starting with the Java 2 SDK, Standard Edition, version 1.3, a
logging stream can be set only if the proper
permission has been granted. Normally this will be done with
the tool PolicyTool, which can be used to grant permission
java.sql.SQLPermission "setLog"
.
DriverManager
's list. Applets can only
deregister drivers from their own classloaders.
The equals
method implements an equivalence relation
on non-null object references:
x
, x.equals(x)
should return
true
.
x
and y
, x.equals(y)
should return true
if and only if
y.equals(x)
returns true
.
x
, y
, and z
, if
x.equals(y)
returns true
and
y.equals(z)
returns true
, then
x.equals(z)
should return true
.
x
and y
, multiple invocations of
x.equals(y) consistently return true
or consistently return false
, provided no
information used in equals
comparisons on the
objects is modified.
x
,
x.equals(null)
should return false
.
The equals method for class Object
implements
the most discriminating possible equivalence relation on objects;
that is, for any non-null reference values x
and
y
, this method returns true
if and only
if x
and y
refer to the same object
(x == y
has the value true
).
Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.
DriverManager
attempts to select an appropriate driver from
the set of registered JDBC drivers.DriverManager
attempts to select an appropriate driver from
the set of registered JDBC drivers.DriverManager
attempts to select an appropriate driver from
the set of registered JDBC drivers.DriverManager
attempts to select an appropriate driver from
the set of registered JDBC drivers.Note: The classname of a driver can be found using
d.getClass().getName()
DriverManager
and all drivers.getLogWriter
and setLogWriter
methods should be used instead
of the get/setlogStream
methods, which are deprecated.java.util.Hashtable
.
The general contract of hashCode
is:
hashCode
method on each of
the two objects must produce the same integer result.
As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)
wait
methods.
The awakened thread will not be able to proceed until the current thread relinquishes the lock on this object. The awakened thread will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened thread enjoys no reliable privilege or disadvantage in being the next thread to lock this object.
This method should only be called by a thread that is the owner of this object's monitor. A thread becomes the owner of the object's monitor in one of three ways:
synchronized
statement
that synchronizes on the object.
Class,
by executing a
synchronized static method of that class.
Only one thread at a time can own an object's monitor.
wait
methods.
The awakened threads will not be able to proceed until the current thread relinquishes the lock on this object. The awakened threads will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened threads enjoy no reliable privilege or disadvantage in being the next thread to lock this object.
This method should only be called by a thread that is the owner
of this object's monitor. See the notify
method for a
description of the ways in which a thread can become the owner of
a monitor.
DriverManager
.
A newly-loaded driver class should call
the method registerDriver
to make itself
known to the DriverManager
.DriverManager
and all drivers.
In the Java 2 SDK, Standard Edition, version 1.3 release, this method checks
to see that there is an SQLPermission
object before setting
the logging stream. If a SecurityManager
exists and its
checkPermission
method denies setting the log writer, this
method throws a java.lang.SecurityException
.
PrintWriter
object
that is used by the DriverManager
and all drivers.
There is a minor versioning problem created by the introduction
of the method setLogWriter
. The
method setLogWriter
cannot create a PrintStream
object
that will be returned by getLogStream
---the Java platform does
not provide a backward conversion. As a result, a new application
that uses setLogWriter
and also uses a JDBC 1.0 driver that uses
getLogStream
will likely not see debugging information written
by that driver.
In the Java 2 SDK, Standard Edition, version 1.3 release, this method checks
to see that there is an SQLPermission
object before setting
the logging stream. If a SecurityManager
exists and its
checkPermission
method denies setting the log writer, this
method throws a java.lang.SecurityException
.
toString
method returns a string that
"textually represents" this object. The result should
be a concise but informative representation that is easy for a
person to read.
It is recommended that all subclasses override this method.
The toString
method for class Object
returns a string consisting of the name of the class of which the
object is an instance, the at-sign character `@
', and
the unsigned hexadecimal representation of the hash code of the
object. In other words, this method returns a string equal to the
value of:
getClass().getName() + '@' + Integer.toHexString(hashCode())
The current thread must own this object's monitor. The thread
releases ownership of this monitor and waits until another thread
notifies threads waiting on this object's monitor to wake up
either through a call to the notify
method or the
notifyAll
method. The thread then waits until it can
re-obtain ownership of the monitor and resumes execution.
As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:
synchronized (obj) { while (<condition does not hold>) obj.wait(); ... // Perform action appropriate to condition }This method should only be called by a thread that is the owner of this object's monitor. See the
notify
method for a
description of the ways in which a thread can become the owner of
a monitor.The current thread must own this object's monitor.
This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. Thread T becomes disabled for thread scheduling purposes and lies dormant until one of four things happens:
A thread can also wake up without being notified, interrupted, or timing out, a so-called spurious wakeup. While this will rarely occur in practice, applications must guard against it by testing for the condition that should have caused the thread to be awakened, and continuing to wait if the condition is not satisfied. In other words, waits should always occur in loops, like this one:
synchronized (obj) { while (<condition does not hold>) obj.wait(timeout); ... // Perform action appropriate to condition }(For more information on this topic, see Section 3.2.3 in Doug Lea's "Concurrent Programming in Java (Second Edition)" (Addison-Wesley, 2000), or Item 50 in Joshua Bloch's "Effective Java Programming Language Guide" (Addison-Wesley, 2001).
If the current thread is interrupted by another thread while it is waiting, then an InterruptedException is thrown. This exception is not thrown until the lock status of this object has been restored as described above.
Note that the wait method, as it places the current thread into the wait set for this object, unlocks only this object; any other objects on which the current thread may be synchronized remain locked while the thread waits.
This method should only be called by a thread that is the owner
of this object's monitor. See the notify
method for a
description of the ways in which a thread can become the owner of
a monitor.
This method is similar to the wait
method of one
argument, but it allows finer control over the amount of time to
wait for a notification before giving up. The amount of real time,
measured in nanoseconds, is given by:
1000000*timeout+nanos
In all other respects, this method does the same thing as the method of one argument. In particular, wait(0, 0) means the same thing as wait(0).
The current thread must own this object's monitor. The thread releases ownership of this monitor and waits until either of the following two conditions has occurred:
notify
method
or the notifyAll
method.
timeout
milliseconds plus nanos
nanoseconds arguments, has
elapsed.
The thread then waits until it can re-obtain ownership of the monitor and resumes execution.
As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:
synchronized (obj) { while (<condition does not hold>) obj.wait(timeout, nanos); ... // Perform action appropriate to condition }This method should only be called by a thread that is the owner of this object's monitor. See the
notify
method for a
description of the ways in which a thread can become the owner of
a monitor.