Oracle8i Enterprise JavaBeans and CORBA Developer's Guide Release 8.1.5 A64683-01 |
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Unlike a conventional Java VM, which compiles and loads Java files, the Oracle8 i JVM compiles and loads schema objects. The three kinds of Java schema objects are:
To make a class file runnable by the Oracle8 i JVM, you use the loadjava
tool to create a Java class schema object from the class file or the source file and load it into a schema. To make a resource file accessible to the JVM, you use loadjava
to create and load a Java resource schema object from the resource file.
The dropjava
tool does the reverse of the loadjava
tool; it deletes schema objects that correspond to Java files. You should always use dropjava
to delete a Java schema object that was created with loadjava
; dropping by means of SQL DDL commands will not update auxiliary data maintained by loadjava
and dropjava
(see "Digest Table").
You must load resource files with loadjava
. If you create .class
files outside the database with a conventional compiler, then you must load them with loadjava
. The alternative to loading class files is to load source files and let the Oracle8 i system compile and manage the resulting class schema objects. In the current Oracle8 i release, most developers will find that compiling and debugging most of their code outside the database and then loading .class
files to debug those files which must be tested inside the database, is the most productive approach. For a particular Java class, you can load either its .class
file or its .java
file, but not both.
loadjava
accepts JAR files that contain either source and resource files or class and resource files (recall that you can load a class's source or its class file but not both). When you pass loadjava
a JAR file or a ZIP file, loadjava
opens the archive and loads its members individually; there is no JAR or ZIP schema object. A file whose content has not changed since the last time it was loaded is not re-loaded (see "Digest Table"), therefore there is little performance penalty for loading JARs. Loading JAR files is the simplest and most foolproof way to use loadjava
.
It is illegal for two schema objects in the same schema to define the same class. For example, suppose a.java
defines class x
and you want to move the definition of x
to b.java
. If a.java
has already been loaded, then loadjava
will reject an attempt to load b.java
(which also defines x
). Instead, do either of the following:
"dropjava"
) a.java
, load b.java
(which defines x
), then load the new a.java
(which does not define x
).
a.java
(which does not define x
), then load b.java
(which defines x
).
Many Java classes contain references to other classes. A conventional JVM searches for classes in the directories, ZIP files, and JARs named in the CLASSPATH. The Oracle8 i JVM, by contrast, searches schemas for class schema objects. Each Oracle8 i class has a resolver spec, which is the Oracle8 i counterpart to the CLASSPATH. For a hypothetical class alpha
, its resolver spec is a list of schemas to search for classes alpha
uses. Notice that resolver specs are per-class, whereas in a classic JVM, CLASSPATH is global to all classes.
In addition to a resolver spec, each class schema object has a list of interclass reference bindings. Each reference list item contains a reference to another class, and one of the following:
An Oracle8 i facility called the resolver maintains reference lists. For each interclass reference in a class, the resolver searches the schemas specified by the class's resolver spec for a valid class schema object that satisfies the reference. If all references are resolved, the resolver marks the class valid. A class that has never been resolved, or has been resolved unsuccessfully, is marked invalid. A class that depends on a schema object that becomes invalid is also marked invalid at the same time; in other words, invalidation cascades upward from a class to the classes that use it and the classes that use them, and so on. When resolving a class that depends on an invalid class, the resolver first tries to resolve the dependency because it may be marked invalid only because it has never been resolved. The resolver does not re-resolve classes that are marked valid.
A class developer can direct loadjava
to resolve classes, or can defer resolution until run time. (The resolver runs automatically when a class tries to load a class that is marked invalid.) It is best to resolve before run time to learn of missing classes early; unsuccessful resolution at run time produces a "class not found" exception. Furthermore, run-time resolution can fail for lack of database resources if the tree of classes is very large.
loadjava
has two resolution modes (in addition to "defer resolution"):
-resolve
option): Loads all classes you specify on the command line, marks them invalid, and then resolves them. Use this mode when initially loading classes that refer to each other, and in general when reloading isolated classes as well. By loading all classes and then resolving them, this mode avoids the error message that occurs if a class refers to a class that will be loaded later in the execution of the command.
-andresolve
option): Resolves each class as it is loaded. In general, this mode is not recommended, especially in combination with a resolver spec that leaves unresolved classes marked valid. For example, suppose you are loading A followed by B, and A refers to B, and you use the following loadjava
arguments (resolver spec notation is described in "resolver"):
-andresolve
-resolver "((* definer's_schema) (* public) (* -))"
A will be resolved before B is loaded; although B is not present, A will be marked valid because the third element of the resolver spec says to mark A valid even though a class it refers to (B) cannot be found. After A, B will be loaded, resolved, and marked valid (assuming its dependencies are satisfied). If you then execute A, it will not be re-resolved because it is marked valid. But if A calls B, you may get an unpredictable exception because A has not been successfully resolved with respect to B.
If you can, it is best to defer resolution until all classes have been loaded; this technique avoids the situation in which the resolver marks a class invalid because a class it uses has not yet been loaded.
The schema object digest table is an optimization that is usually invisible to developers. The digest table enables loadjava
to skip files that have not changed since they were last loaded. This feature improves the performance of makefiles and scripts that invoke loadjava
for collections of files, only some of which need to be re-loaded. A re-loaded archive file might also contain some files that have changed since they were last loaded and some that have not.
The loadjava
tool detects unchanged files by maintaining a digest table in each schema. The digest table relates a file name to a digest, which is a shorthand representation of the file's content (a hash). Comparing digests computed for the same file at different times is a fast way to detect a change in the file's content--much faster than comparing every byte in the file. For each file it processes, loadjava
computes a digest of the file's content and then looks up the file name in the digest table. If the digest table contains an entry for the file name that has the identical digest, then loadjava
does not load the file because a corresponding schema object exists and is up to date. If you invoke loadjava
with the -verbose
option, then it will show you the results of its digest table lookups.
Normally, the digest table is invisible to developers because loadjava
and dropjava
keep it synchronized with schema object additions, changes, and deletions. For this reason, always use dropjava
to delete a schema object that was created with loadjava
, even if you know how to drop a schema object with DDL. If the digest table becomes corrupted (loadjava
does not update a schema object whose file has changed), use loadjava
's -force
option to bypass the digest table lookup.
Loading a source file creates or updates a Java source schema object and invalidates the class schema object(s) previously derived from the source. (If the class schema objects don't exist, loadjava
creates them.) loadjava
invalidates the old class schema objects because they were not compiled from the newly loaded source. Compilation of a newly loaded source, called for instance A, is automatically triggered by any of the following conditions:
To force compilation when you load a source file, use the loadjava
-resolve
or -andresolve
option.
The compiler writes error messages to the predefined USER_ERRORS
view; loadjava
retrieves and displays the messages produced by its compiler invocations. See the Oracle8i Reference for a description of this table.
The compiler recognizes two options which are described in this section, encoding
and online
. There are two ways to specify options to the compiler. If you run loadjava
with one of the resolve options (which may trigger compilation), then you can specify compiler options on the command line.
You can additionally specify persistent compiler options in a per-schema database table called JAVA$OPTIONS
which you create as described shortly. You can use the JAVA$OPTIONS
table for default compiler options, which you can override selectively with a loadjava
command-line option.
A JAVA$OPTIONS
row contains the names of source schema objects to which an option setting applies; you can use multiple rows to set the options differently for different source schema objects. The compiler looks up options in the JAVA$OPTIONS
table when it has been invoked without a command line (that is, by the class loader), or when the command line does not specify an option. When compiling a source schema object for which there is neither a JAVA$OPTIONS
entry nor a command line value for an option, the compiler assumes a default value as follows:
encoding
= latin1
: see Table 6-2 for a description of this option.
online
= true
: see the Oracle8i SQLJ Developer's Guide and Reference for a description of this option, which only applies to Java sources that contain SQLJ constructs.
You can set JAVA$OPTIONS
entries by means of the following functions and procedures, which are defined in the database package DBMS_JAVA
:
PROCEDURE set_compiler_option(name VARCHAR2, option VARCHAR2, value VARCHAR2);
FUNCTION get_compiler_option(name VARCHAR2, option VARCHAR2) RETURNS VARCHAR2;
PROCEDURE reset_compiler_option(name VARCHAR2, option VARCHAR2);
The name
parameter is a Java package name, or a fully qualified class name, or the empty string. When the compiler searches the JAVA$OPTIONS
table for the options to use for compiling a Java source schema object, it uses the row whose name
most closely matches the schema object's fully qualified class name. For examples, see Table 6-1 . A name
whose value is the empty string matches any schema object name.
The option
parameter is either 'online'
or 'encoding'
. For the value
s you can specify for these options, see Table 6-2 and the Oracle8i SQLJ Developer's Guide and Reference , respectively.
A schema does not initially have a JAVA$OPTIONS
table. To create a JAVA$OPTIONS
table, use the DBMS_JAVA
package's java.set_compiler_option
procedure to set a value; the procedure will create the table if it does not exist. Specify parameters in single quotes. For example:
SQL> execute dbms_java.set_compiler_option('x.y', 'online', 'false');
Table 6-1 represents a hypothetical JAVA$OPTIONS
database table. Because the table has no entry for the encoding
option, the compiler will use the default or the value specified on the command line. The online
options shown in the table match schema object names as follows:
a.b.c.d
matches class and package names beginning with a.b.c.d
; they will be compiled with online
= true
.
a.b
matches class and package names beginning with a.b
but not a.b.c.d
; they will be compiled with online
= false
.
online
= true
.
Table 6-1 Example JAVA$OPTIONS Table and Matching Examples
JAVA$OPTIONS Entries |
Match Examples | ||
---|---|---|---|
Name | Option | Value | |
|
|
|
|
|
|
|
|
(empty string) |
|
|
|
The loadjava
tool creates schema objects from files and loads them into a schema. Schema objects can be created from Java source files, class files, and resource files, and the same kinds of files in uncompressed ZIP and Java archives (JARs). loadjava
can also create schema objects from SQLJ files; the Oracle8i SQLJ Developer's Guide and Reference describes how to use loadjava
with SQLJ. You must have the CREATE PROCEDURE privilege to load into your schema, and the CREATE ANY PROCEDURE privilege to load into another schema.
loadjava {-user | -u} <user>/<password>[@<database>] [options] <file>.java | <file>.class | <file>.jar | <file>.zip | <file>.sqlj | <resourcefile>} ... [{-a | -andresolve}] [-debug] [{-d | -definer}] [{-e | -encoding} <encoding_scheme>] [{-f | -force}] [{-g | -grant} {<user> | <role>}[,{<user> | <role>}]...] [{-o | -oci8}] [-oracleresolver] [{-r | -resolve}] [{-R | -resolver} "resolver_spec"] [{-S | -schema} <schema>] [{-s | -synonym}] [{-t | -thin}] [{-v | -verbose}]
Table 6-2 summarizes the loadjava
arguments. If you execute loadjava
multiple times specifying the same files and different options, the options specified in the most recent invocation hold. There are two exceptions:
loadjava
does not load a file because it matches a digest table entry, most options on the command line have no effect on the schema object. The exceptions are -grant
, -resolve
, and -andresolve
, which are always obeyed. Use the -force
option to direct loadjava
to skip the digest table lookup.
-grant
option is cumulative; every user or role specified in every loadjava
invocation for a given class in a given schema has the EXECUTE privilege.
Table 6-2 loadjava Argument Summary
Argument | Description |
---|---|
<filenames> |
You can specify any number and combination of |
|
Directs |
-debug |
Directs the Java compiler to generate debug information; equivalent to |
|
By default, class schema objects run with the privileges of their invoker. This option confers definer (the developer who invokes |
|
Identifies the source file encoding for the compiler, overriding the matching value, if any, in the |
|
Forces files to be loaded even if they match digest table entries. |
|
Grants the EXECUTE privilege on loaded classes to the listed users and/or roles. (To call the methods of a class, users must have the EXECUTE privilege.) Any number and combination of user and role names can be specified, separated by commas but not spaces ( To grant the EXECUTE privilege on an object in someone else's schema requires that the original CREATE PROCEDURE privilege was granted with WITH GRANT options. |
|
Directs |
-oracleresolver |
Shorthand for: -resolver '((* definer's_schema) (* public))'
|
|
Compiles (if necessary) and resolves external references in classes after all classes on the command line have been loaded. |
|
Specifies an explicit resolver spec, which is bound to the newly loaded classes. |
|
Designates the schema where schema objects are created. If not specified, the logon schema is used. To create a schema object in a schema that is not your own, you must have the CREATE PROCEDURE or CREATE ANY PROCEDURE privilege. |
|
Creates a PUBLIC synonym for loaded classes making them accessible outside the schema into which they are loaded. To specify this option, you must have the CREATE PUBLIC SYNONYM privilege. If |
|
Directs |
|
Specifies a user, password, and database connect string; the files will be loaded into this database instance. The argument has the form |
|
Directs loadjava to emit detailed status messages while running. Use |
This section describes the details of loadjava
arguments whose behavior is more complex than the summary descriptions contained in Table 6-2.
You can specify as many .class
, .java
, .sqlj
,.jar
, .zip
, and resource files as you like, in any order. If you specify a JAR or ZIP file, then loadjava
processes the files in the JAR or ZIP; there is no JAR or ZIP schema object. If a JAR or ZIP contains a JAR or ZIP, loadjava
does not process them.
The best way to load files is to put them in a JAR or ZIP and then load the archive. Loading archives avoids the resource schema object naming complications described later in this section. If you have a JAR or ZIP that works with the JDK, then you can be sure that loading it with loadjava
will also work, without having to learn anything about resource schema object naming.
Schema object names are slightly different from file names, and loadjava
names different types of schema objects differently. Because class files are self-identifying (they contain their names), loadjava
's mapping of class file names to schema object names is invisible to developers. Source file name mapping is also invisible to developers; loadjava
gives the schema object the fully qualified name of the first class defined in the file. JAR and ZIP files also contain the names of their files; however, resource files are not self identifying. loadjava
generates Java resource schema object names from the literal names you supply as arguments (or the literal names in a JAR or ZIP file). Because running classes use resource schema objects, it is important that you specify resource file names correctly on the command line, and the correct specification is not always intuitive. The surefire way to load individual resource files correctly is:
Run loadjava
from the top of the package tree and specify resource file names relative to that directory. (The "top of the package tree" is the directory you would name in a Java CLASSPATH list.)
If you do not want to follow this rule, observe the details of resource file naming that follow. When you load a resource file, loadjava
generates the resource schema object name from the resource file name as literally specified on the command line. Suppose, for example you type:
% cd /home/scott/javastuff % loadjavaoptions
alpha/beta/x.properties % loadjavaoptions
/home/scott/javastuff/alpha/beta/x.properties
Although you have specified the same file with a relative and an absolute path name, loadjava
creates two schema objects, one called alpha/beta/x.properties
, the other ROOT/home/scott/javastuff/alpha/beta/x.properties
. (loadjava
prepends ROOT
because schema object names cannot begin with the "/
" character; however, that is an implementation detail that is unimportant to developers.) The important point is that a resource schema object's name is generated from the file name as entered.
Classes can refer to resource files relatively (for example, b.properties
) or absolutely (for example, /a/b.properties
). To ensure that loadjava
and the class loader use the same name for a schema object, follow this rule when loading resource files:
Enter the name on the command line that the class passes to getResource() or getResourceAsString().
Instead of remembering whether classes use relative or absolute resource names and changing directories so that you can enter the correct name on the command line, you can load resource files in a JAR as follows:
% cd /home/scott/javastuff
% jar -cf alpharesources.jar alpha/*.properties
% loadjava options
alpharesources.jar
Or, to simplify further, put both the class and resource files in a JAR, which makes the following invocations equivalent:
% loadjavaoptions
alpha.jar % loadjavaoptions
/home/scott/javastuff/alpha.jar
The two loadjava
commands in this example make the point that you can use any pathname to load the contents of a JAR file. Note as well that even if you did execute the redundant commands shown above, loadjava
would realize from the digest table that it did not need to load the files twice. That means that re-loading JAR files is not as time-consuming as it might seem even when few files have changed between loadjava
invocations.
The -definer
option is identical to definer's rights in stored procedures and is conceptually similar to the Unix setuid
facility; however, whereas setuid
applies to a complete program, you can apply -definer
class by class. Moreover, different definers may have different privileges. Because an application may consist of many classes, you must apply -definer
with care to achieve the results desired, namely classes that run with the privileges they need but no more. For more information on definer's rights, see the Oracle8i Java Stored Procedures Developer's Guide.
Use -resolve
to force loadjava
to compile (if necessary) and resolve a class that has previously been loaded. It is not necessary to specify -force
because resolution is performed after, and independently of, loading; however, note that -andresolve
does not resolve previously loaded classes.
This option associates an explicit resolver spec with the class schema objects that loadjava
creates or replaces.
A resolver spec consists of one or more items, each of which consists of a name spec and a schema spec expressed in the following syntax:
"((name_spec schema_spec) [(name_spec schema_spec)] ...)"
import
statement. It can be a fully qualified Java class name, or a package name whose final element is the wildcard character "*
", or (unlike an imported package name) simply the wildcard character "*
"; however, the elements of a name spec must be separated by "/
" characters, not periods. For example, the name spec a/b/*
matches all classes whose names begin with a.b.
. The special name spec *
matches all class names.
-"
. The wildcard does not identify a schema but directs the resolve operation to not mark a class invalid because a reference to a matching name cannot be resolved. (Without a "-"
wildcard in a resolver spec, an unresolved reference in the class makes the class invalid and produces an error message.) Use a "-"
wildcard when you must test a class that refers to a class you cannot or do not want to load; for example, GUI classes that a class refers to but does not call because when run in the server there is no GUI.
The resolution operation interprets a resolver spec item as follows:
When looking for a schema object whose name matches the name spec, look in the schema named by the partner schema spec.
The resolution operation searches schemas in the order in which the resolver spec lists them. For example,
-resolver '((* SCOTT) (* PUBLIC))'
means
Search for any reference first in SCOTT and then in PUBLIC. If a reference is not resolved, then mark the referring class invalid and display an error message; in other words, call attention to missing classes.
For a developer named Scott, this resolver spec is equivalent to the -oracleresolver
spec.
The following example:
-resolver "((* SCOTT) (* PUBLIC) (my/gui/* -))"
means
Search for any reference first in SCOTT and then in PUBLIC. If the reference is not found, and is to a class in the package my.gui then mark the referring class valid, and do not display an error; in other words, ignore missing classes in this package. If the reference is not found and is not to a class in my.gui, then mark the referring class invalid and produce an error message.
The permissible forms of @<database>
depend on whether you specify -oci8
or -thin
; -oci8
is the default.
-oci8
: @<database>
is optional; if you do not specify, then loadjava
uses the user's default database. If specified, <database>
can be a TNS name or a Net8 name-value list.
-thin
: @<database>
is required. The format is <host>:<lport>:<SID>
.
Here are examples of loadjava
commands:
loadjava -u scott/tiger -resolve -schema TEST ServerObjects.jar
loadjava -thin -u scott/tiger@dbhost:5521:orcl \ -andresolve alpha.class beta.props
alpha.class
:
loadjava -thin -schema test -u scott/tiger@localhost:5521:orcl \ -grant Betty,Bob alpha.class
The dropjava
tool is the converse of loadjava
. It transforms command-line file names and uncompressed JAR or ZIP file contents to schema object names, then drops the schema objects and deletes their corresponding digest table rows. You can enter .java
, .class
, .sqlj
, .zip
, .jar
, and resource file names on the command line in any order. The Oracle8i SQLJ Developer's Guide and Reference describes how to use loadjava
and dropjava
with SQLJ.
Dropping a class invalidates classes that depend on it, recursively cascading upwards. Dropping a source drops classes derived from it.
dropjava {-u | -user} <user>/<password>[@<database>] [options] {<file>.java | <file>.class | file.sqlj | <file>.jar | <file.zip> | <resourcefile>} ... [{-o | -oci8}] [{-S | -schema} <schema>] [{-t | -thin}] [{-v | -verbose}]
Table 6-3 summarizes the dropjava
arguments.
Argument | Description |
---|---|
|
Specifies a user, password, and optional database connect string; the files will be dropped from this database instance. See "user" for details. |
<filenames> |
You can specify any number and combination of |
|
Directs |
|
Designates the schema from which schema objects are dropped. If not specified, the logon schema is used. To drop a schema object from a schema that is not your own, you need the DROP ANY PROCEDURE system privilege. |
|
Directs |
|
Directs |
dropjava
interprets most file names as loadjava
does:
.class
files: dropjava
finds the class name in the file and drops the corresponding schema object.
.java
and .sqlj
files: dropjava
finds the first class name in the file and drops the corresponding schema object.
.jar
and .zip
files: dropjava
processes the archived file names as if they had been entered on the command line.
If a file name has another extension or no extension, then dropjava
interprets the file name as a schema object name and drops all source, class, and resource objects that match the name. For example, the hypothetical file name alpha
drops whichever of the following exists: the source schema object named alpha
, the class schema object named alpha
, and the resource schema object named alpha
. If the file name begins with the "/
" character, then dropjava
prepends ROOT
to the schema object name.
If dropjava
encounters a file name that does not match a schema object, it displays a message and processes the remaining file names.
The permissible forms of @<database>
depend on whether you specify -oci8
or -thin
; -oci8
is the default.
-oci8
: @<database>
is optional; if you do not specify, then dropjava
uses the user's default database. If specified, then <database>
can be a TNS name or a Net8 name-value list.
-thin
: @<database>
is required. The format is <host>:<lport>:<SID>
.
Here are some dropjava
examples.
TEST
in the default database that were loaded from ServerObjects.jar
:
dropjava -u scott/tiger -schema TEST ServerObjects.jar
dropjava -thin -u scott/tiger@dbhost:5521:orcl alpha.class beta.props