faq.so

berkeley db 4.6.21的源码。berkeley db是一个简单的数据库管理系统

m4_comment([$Id: faq.so,v 1.16 2007/07/11 11:13:30 mjc Exp $])

m4_ref_title(Java API,
    Java FAQ, [Java @FAQ, Java FAQ], java/program, arch/bigpic)

m4_nlistbegin

m4_nlist([dnl
m4_bold([On what platforms is the m4_db Java API supported?])

m4_p([dnl
All platforms supported by m4_db that have a JVM compatible with J2SE
1.4 or above.])])

m4_nlist([dnl
m4_bold([How does the m4_db Java API relate to the J2EE standard?])

m4_p([dnl
The m4_db Java API does not currently implement any part of the J2EE
standard.  That said, it does implement the implicit standard for Java
m4_linkweb(http://java.sun.com/j2se/1.5.0/docs/guide/collections/,dnl
[Java Collections]).  The concept of a transaction exists in several
Java packages (J2EE, XA, JINI to name a few).  Support for these APIs
will be added based on demand in future versions of m4_db.])])

m4_nlist([dnl
m4_bold([How should I incorporate db.jar and the db native library into
a Tomcat or other J2EE application servers?])

m4_p([dnl
Tomcat and other J2EE application servers have the ability to rebuild
and reload code automatically.  When using Tomcat this is the case when
"reloadable" is set to "true".  If your WAR file includes the db.jar it
too will be reloaded each time your code is reloaded.  This causes
exceptions as the native library can't be loaded more than once and
there is no way to unload native code.  The solution is to place the
db.jar in $TOMCAT_HOME/common/lib and let Tomcat load that library once
at start time rather than putting it into the WAR that gets reloaded
over and over.])])

m4_nlist([dnl
m4_bold([Can I use the m4_db Java API from within a EJB, a Servlet or a
JSP page?])

m4_p([dnl
Yes.  The m4_db Java API can be used from within all the popular J2EE
application servers in many different ways.])])

m4_nlist([dnl
m4_bold([During one of the first calls to the m4_db Java API, a
DbException is thrown with a "Bad file number" or "Bad file descriptor"
message.])

m4_p([dnl
There are known large-file support bugs under JNI in various releases
of the JDK.  Please upgrade to the latest release of the JDK, and, if
that does not solve the problem, disable big file support using the
--disable-largefile configuration option.])])

m4_nlist([dnl
m4_bold([How can I use native methods from a debug build of the
Java library?])

m4_p([dnl
Set Java's library path so that the debug version of m4_db's Java
library appears, but the release version does not.  m4_db tries to load
the release library first, and if that fails tries the debug library.])])

m4_nlist([dnl
m4_bold([Why is ClassNotFoundException thrown when adding a record to
the database, when a SerialBinding is used?])

m4_p([dnl
This problem occurs if you copy the db.jar file into the Java extensions
(ext) directory.  This will cause the database code to run under the
System class loader, and it won't be able to find your application
classes.])

m4_p([dnl
You'll have to actually remove db.jar from the Java extension directory.
If you have more than one installation of Java, be sure to remove it
from all of them.  This is necessary even if db.jar is specified in the
classpath.])

m4_p([dnl
An example of the exception is:])
m4_indent([dnl
collections.ship.basic.SupplierKey
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at com.sleepycat.bind.serial.StoredClassCatalog.getClassInfo(StoredClassCatalog.java:211)
...])])

m4_nlist([dnl
m4_bold([I'm upgrading my Java application to m4_db 4.3.  Can I use the
com.sleepycat.db.internal package rather than porting my code to the new
API?])

m4_p([dnl
While it is possible to use the low-level API from applications, there
are some caveats that should be considered when upgrading.  The first is
that the internal API depends on some classes in the public API such as
DatabaseEntry.])

m4_p([dnl
In addition, the internal API is closer to the C API and doesn't have
some of the default settings that were part of the earlier Java API.
For example, applications will need to set the DB_THREAD flag explicitly
if handles are to be used from multiple threads, or subtle errors may
occur.])])

m4_nlistend

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