Skip Headers

Oracle Application Server Containers for J2EE JSP Tag Libraries and Utilities Reference 10g (9.0.4) Part Number B10319-01 |
Home | Contents | Index

# A
JML Compile-Time Syntax and Tags

The JSP tag library framework was introduced in the JSP 1.1 specification. Oracle JSP releases prior to the implementation of the JSP 1.1 specification could support JML tags only as Oracle-specific translator extensions. This is referred to as compile-time tag support in this manual.

JSP releases with OC4J continue to support the compile-time JML implementation; however, it is generally advisable to use the standards-compliant runtime implementation whenever possible. The runtime implementation is documented in Chapter 3, "JSP Markup Language Tags".

This appendix discusses features of the compile-time implementation that are not in common with the runtime implementation, and consists of the following sections:

- JML Compile-Time Syntax Support

- JML Compile-Time Tag Support

For a general discussion of when it might be advantageous to use a compile-time implementation, refer to the Oracle Application Server Containers for J2EE Support for JavaServer Pages Developer's Guide.

## JML Compile-Time Syntax Support

The following sections describe Oracle-specific bean reference syntax and expression syntax supported by the compile-time JML implementation for specifying tag attribute values:

- JML Bean References and Expressions, Compile-Time Implementation

- Attribute Settings with JML Expressions

This functionality requires the OC4J JSP translator; it is not portable to other JSP environments.

### JML Bean References and Expressions, Compile-Time Implementation

A bean reference is any reference to a JavaBean instance that results in accessing either a property or a method of the bean. This includes a reference to a property or method of a bean where the bean itself is a property of another bean.

This becomes cumbersome, because standard JavaBeans syntax requires that properties be accessed by calling their accessor methods rather than by direct reference. For example, consider the following direct reference:

    a.b.c.d.doIt()

This must be expressed as follows in standard JavaBeans syntax:

    a.getB().getC().getD().doIt()

The Oracle compile-time JML implementation, however, offers abbreviated syntax, as described in the following subsections.

#### JML Bean References

Oracle-specific syntax supported by the compile-time JML implementation allows bean references to be expressed using direct dot (".") notation. Note that standard bean property accessor method syntax is also still valid.

Consider the following standard JavaBean reference:

    customer.getName()

In JML bean reference syntax, you can express this in either of the following ways:

    customer.getName()

or:

    customer.name

JavaBeans can optionally have a default property whose reference is assumed if no reference is explicitly stated. You can omit default property names in JML bean references. In the example above, if `name` is the default property, then the following are all valid JML bean references:

    customer.getName()

or:

    customer.name

or:

    customer

Most JavaBeans do not define a default property. Of those that do, the most significant are the JML datatype JavaBeans described in Chapter 2, "JavaBeans for Extended Types".

#### JML Expressions

JML expression syntax supported by the compile-time JML implementation is a superset of standard JSP expression syntax, adding support for the JML bean reference syntax documented in the preceding section.

A JML bean reference appearing in a JML expression must be enclosed in the following syntax:

    $[JML_bean_reference]

### Attribute Settings with JML Expressions

Tag attribute documentation under "JSP Markup Language (JML) Tag Descriptions" notes standards-compliant syntax. You can set attributes, as documented there, for either the runtime or the compile-time JML implementation and even for non-Oracle JSP environments.

If you intend to use only the Oracle-specific compile-time implementation, however, you can set attributes using JML bean references and JML expression syntax, as documented in the preceding section, "JML Bean References and Expressions, Compile-Time Implementation". Note the requirements that follow.

- Wherever Chapter 3 documents an attribute that accepts either a string literal or an expression, you can use a JML expression in its `$[...]` syntax inside standard JSP `<%=...%>` syntax.

  Consider an example using the JML `useVariable` tag. You would use syntax such as the following for the runtime implementation:

      <jml:useVariable id = "isValidUser" type = "boolean" value = "<%= dbConn.isValid() %>" scope = "session" />

  You can alternatively use syntax such as the following for the compile-time implementation (the `value` attribute can be either a string literal or an expression):

      <jml:useVariable id = "isValidUser" type = "boolean" value = "<%= $[dbConn.valid] %>" scope = "session" />

- Wherever Chapter 3 documents an attribute that accepts an expression only, you can use a JML expression in its `$[...]` syntax without being nested in `<%=...%>` syntax.

  Consider an example using JML `choose...when` tags. You would use something such as the following syntax for the runtime implementation (presuming `orderedItem` is a `JmlBoolean` instance):

      <jml:choose>
           <jml:when condition = "<%= orderedItem.getValue() %>"  >
                     You have changed your order:
                   -- outputs the current order --
           </jml:when>
           <jml:otherwise>
                     Are you sure we can't interest you in something?
           </jml:otherwise>
      </jml:choose>

  You can alternatively use syntax such as the following for the compile-time implementation, where the `condition` attribute can be an expression only:

      <jml:choose>
           <jml:when condition = "$[orderedItem]"  >
                     You have changed your order:
                   -- outputs the current order --
           </jml:when>
           <jml:otherwise>
                     Are you sure we can't interest you in something?
           </jml:otherwise>
      </jml:choose>

## JML Compile-Time Tag Support

This section presents the following:

- Documentation of the `taglib` directive that you must use for compile-time JML support

- Summary of all compile-time tags, noting which are desupported in the runtime implementation

- Description of tags supported by the compile-time implementation that are desupported in the runtime implementation

  Tags still supported in the runtime implementation are documented in "JSP Markup Language (JML) Tag Descriptions".

Note: In most cases, JML tags that are desupported in the runtime implementation have standard JSP equivalents. Some of the compile-time tags, however, were desupported because they have functionality that is difficult to implement when adhering to the current JSP specification.

### The taglib Directive for Compile-Time JML Support

The Oracle compile-time JML support implementation uses a custom class, `OpenJspRegisterLib`, to implement JML tag support.

In a JSP page using JML tags with the compile-time implementation, the `taglib` directive must specify the fully qualified name of this class, instead of specifying a TLD file as in standard JSP tag library usage:

    <%@ taglib uri="oracle.jsp.parse.OpenJspRegisterLib" prefix="jml" %>

For information about usage of the `taglib` directive for the JML runtime implementation, see "Overview of the JSP Markup Language (JML) Tag Library".

### JML Tag Summary, Compile-Time Versus Runtime

Most JML tags are available in both the runtime model and the compile-time model; however, there are exceptions, as summarized in Table A-1.

##### Table A-1 JML Tags Supported: Compile-Time Model Versus Runtime Model

Tag | Supported in Oracle Compile-Time Implementation? | Supported in Oracle Runtime Implementation?
--- | --- | ---
Bean Binding Tags: |  |
useBean | Yes | No; use `jsp:useBean`.
useVariable | Yes | Yes
useForm | Yes | Yes
useCookie | Yes | Yes
remove | Yes | Yes
Bean Manipulation Tags: |  |
getProperty | Yes | No; use `jsp:getProperty`.
setProperty | Yes | No; use `jsp:setProperty`.
set | Yes | No
call | Yes | No
lock | Yes | No
Control Flow Tags: |  |
if | Yes | Yes
choose | Yes | Yes
for | Yes | Yes
foreach | Yes; `type` attribute is optional. | Yes; `type` attribute is required.
return | Yes | Yes
flush | Yes | Yes
include | Yes | No; use `jsp:include`.
forward | Yes | No; use `jsp:forward`.
XML Tags: |  |
transform | Deprecated | Yes
styleSheet | Deprecated | Yes
Utility Tags: |  |
print | Yes; use double-quotes to specify a string literal. | No; use JSP expressions.
plugin | Yes | No; use `jsp:plugin`.

Note: Since Oracle9iAS Release 2 (9.0.3), the `transform` and `styleSheet` tags are deprecated in the compile-time implementation.

### Descriptions of Additional JML Tags, Compile-Time Implementation

The following sections provide detailed descriptions of JML tags that are still supported by the JML compile-time implementation but are not supported by the JML runtime implementation. The tags supported in the runtime implementation are documented under "JSP Markup Language (JML) Tag Descriptions".

- JML useBean Tag

- JML getProperty Tag

- JML setProperty Tag

- JML set Tag

- JML call Tag

- JML lock Tag

- JML include Tag

- JML forward Tag

- JML print Tag

- JML plugin Tag

Notes: The prefix "jml:" is used in the tag syntax here. This is by convention but is not required. You can specify any desired prefix in your `taglib` directive. See "Tag Syntax Symbology and Notes" for general information about tag syntax conventions in this manual.

#### JML useBean Tag

This tag declares an object to be used in the page, locating the previously instantiated object at the specified scope by name if it exists. If it does not exist, the tag creates a new instance of the appropriate class and attaches it to the specified scope by name.

The syntax and semantics are the same as for the standard `jsp:useBean` tag, except that wherever a JSP expression is valid in `jsp:useBean` usage, either a JML expression or a JSP expression is valid in JML `useBean` usage.

You can refer to the Oracle Application Server Containers for J2EE Support for JavaServer Pages Developer's Guide for an overview of the `jsp:useBean` tag.

##### Syntax

    <jml:useBean id = "beanInstanceName"
    [ scope ="page" | "request" | "session" | "application" ]
      class ="package.class" |
      type = "package.class" |
      class ="package.class" type = "package.class" |
      beanName = "package.class" | "<%= jmlExpression %>" type = "package.class"  />

Alternatively, you can have additional nested tags, such as `setProperty` tags, and use a `</jml:useBean>` end-tag.

##### Attributes

In addition to specifying `id`, you must specify `class`, `type` (or `class` and `type`), or `beanName`.

Refer to the Sun Microsystems JavaServer Pages Specification for detailed information about `jsp:useBean` attributes and their syntax.

##### Example

    <jml:useBean id = "isValidUser" class = "oracle.jsp.jml.JmlBoolean" scope = "session" />

#### JML getProperty Tag

This tag is functionally identical to the standard `jsp:getProperty` tag. It prints the value of the bean property into the response.

For general information about `getProperty` usage, refer to the Oracle Application Server Containers for J2EE Support for JavaServer Pages Developer's Guide or the Sun Microsystems JavaServer Pages Specification.

##### Syntax

    <jml:getProperty name = "beanInstanceName"
                     property = "propertyName" />

##### Attributes

- `name` (required): This is the name of the bean whose property is being retrieved.

- `property` (required): This is the name of the property being retrieved.

##### Example

The following example outputs the current value of the `salary` property. Assume `salary` is of type `JmlNumber`.

    <jml:getProperty name="salary" property="value" />

This is equivalent to the following:

    <%= salary.getValue() %>

#### JML setProperty Tag

This tag covers the functionality supported by the standard `jsp:setProperty` tag and adds functionality to support JML expressions. In particular, you can use JML bean references.

For general information about `setProperty` usage, refer to the Oracle Application Server Containers for J2EE Support for JavaServer Pages Developer's Guide or the Sun Microsystems JavaServer Pages Specification.

##### Syntax

    <jml:setProperty name = "beanInstanceName"
                     property = " * " |
                     property = "propertyName" [ param = "parameterName" ] |
                     property = "propertyName"
                   [ value = "stringLiteral" | "<%= jmlExpression %>" ] />

##### Attributes

- `name` (required): This is the name of the bean whose property is being set.

- `property` (required): This is the name of the property being set.

- `value`: This is an optional parameter that lets you set the value directly instead of from a request parameter. The JML `setProperty` tag supports JML expressions in addition to standard JSP expressions to specify the value.

##### Example

The following example updates `salary` with a six percent raise. Assume `salary` is of type `JmlNumber`.

    <jml:setProperty name="salary" property="value" value="<%= $[salary] * 1.06 %>" />

This is equivalent to the following:

    <% salary.setValue(salary.getValue() * 1.06); %>

#### JML set Tag

This tag provides an alternative for setting a bean property, using syntax that is more convenient than that of the `setProperty` tag.

##### Syntax

    <jml:set name = "beanInstanceName.propertyName"
             value = "stringLiteral" | "<%= jmlExpression %>" />

##### Attributes

- `name` (required): This is a direct reference (JML bean reference) to the bean property to be set.

- `value` (required): This is the new property value. It is expressed either as a string literal, a JML expression, or a standard JSP expression.

##### Example

Each of the following examples updates `salary` with a six percent raise. Assume `salary` is of type `JmlNumber`.

    <jml:set name="salary.value" value="<%= salary.getValue() * 1.06 %>" />

or:

    <jml:set name="salary.value" value="<%= $[salary.value] * 1.06 %>" />

or:

    <jml:set name="salary" value="<%= $[salary] * 1.06 %>" />

These are equivalent to the following:

    <% salary.setValue(salary.getValue() * 1.06); %>

#### JML call Tag

This tag provides a mechanism to invoke bean methods that return nothing.

##### Syntax

    <jml:call method = "beanInstanceName.methodName(parameters)" />

##### Attributes

- `method` (required): This is the method call as you would write it in a scriptlet, except that the `beanInstancename.methodName` portion of the statement can be written as a JML bean reference if enclosed in JML expression `$[... ]` syntax.

##### Example

The following example redirects the client to a different page:

    <jml:call name='response.sendRedirect("http://www.oracle.com/")' />

This is equivalent to the following:

    <% response.sendRedirect("http://www.oracle.com/"); %>

#### JML lock Tag

This tag allows controlled, synchronous access to the named object for any code that uses it within the tag body.

Generally, JSP developers need not be concerned with concurrency issues. However, because application-scope objects are shared across all users running the application, access to critical data must be controlled and coordinated.

You can use the JML `lock` tag to prevent concurrent updates by different users.

##### Syntax

    <jml:lock name = "beanInstanceName" >
       ...body...
    </jml:lock>

##### Attributes

- `name` (required): This is the name of the object that should be locked during execution of code in the `lock` tag body.

##### Example

In the following example, `pageCount` is an application-scope `JmlNumber` value. The variable is locked to prevent the value from being updated by another user between the time this code gets the current value and the time it sets the new value.

    <jml:lock name="pageCount" >
        <jml:set name="pageCount.value" value="<%= pageCount.getValue() + 1 %>" />
    </jml:lock>

This is equivalent to the following:

    <% synchronized(pageCount)
       {
          pageCount.setValue(pageCount.getValue() + 1);
       }
    %>

#### JML include Tag

This tag includes the output of another JSP page, a servlet, or an HTML page in the response of the including page (the page invoking `include`). It provides the same functionality as the standard `jsp:include` tag except that the `page` attribute can also be expressed as a JML expression.

For general information about `include` usage, refer to the Oracle Application Server Containers for J2EE Support for JavaServer Pages Developer's Guide or the Sun Microsystems JavaServer Pages Specification.

##### Syntax

    <jml:include page = "relativeURL" | "<%= jmlExpression %>"
                 flush = "true" | "false" />

##### Attributes

For general information about `include` attributes and usage, refer to the Sun Microsystems JavaServer Pages Specification.

##### Example

The following example includes the output of `table.jsp`, a presentation component that renders an HTML table based on data in the query string and request attributes.

    <jml:include page="table.jsp?maxRows=10" flush="true" />

#### JML forward Tag

This tag forwards the request to another JSP page, a servlet, or an HTML page. It provides the same functionality as the standard `jsp:forward` tag except that the `page` attribute can also be expressed as a JML expression.

For general information about `forward` usage, refer to the Oracle Application Server Containers for J2EE Support for JavaServer Pages Developer's Guide.

##### Syntax

    <jml:forward page = "relativeURL" | "<%= jmlExpression %>" />

##### Attributes

For general information about `forward` attributes, refer to the Sun Microsystems JavaServer Pages Specification.

##### Example

    <jml:forward page="altpage.jsp" />

#### JML print Tag

This tag provides essentially the same functionality as a standard JSP expression: `<%=` `expr``%>`. A specified JML expression or string literal is evaluated and the result is output into the response. With this tag, the JML expression does not have to be enclosed in `<%= ... %>` syntax; however, a string literal must be enclosed in double-quotes.

##### Syntax

    <jml:print eval = '"stringLiteral"' | "jmlExpression" />

##### Attributes

- `eval` (required): Specifies the string or expression to be evaluated and output.

##### Examples

Either of the following examples outputs the current value of `salary`, which is of type `JmlNumber`:

    <jml:print eval="$[salary]" />

or:

    <jml:print eval="salary.getValue()" />

The following example prints a string literal:

    <jml:print eval='"Your string here"' />

#### JML plugin Tag

This tag has functionality identical to that of the standard `jsp:plugin` tag.

For general information about `plugin` usage, refer to the Oracle Application Server Containers for J2EE Support for JavaServer Pages Developer's Guide or the Sun Microsystems JavaServer Pages Specification.

| Copyright © 2002, 2003 Oracle Corporation. All Rights Reserved. |
Home | Contents | Index