Home Testing Expand child menu Expand. SAP Expand child menu Expand. Web Expand child menu Expand. Must Learn Expand child menu Expand. Big Data Expand child menu Expand. Live Project Expand child menu Expand. A tag attribute is communicated between the calling page and the tag file when the tag is invoked.
No further communication occurs between the calling page and the tag file. The variable is not initialized by the calling page but instead is set by the tag file. Each type of parameter is synchronized with the calling page at various points according to the scope of the variable. See Variable Synchronization for details. To declare an EL variable exposed by a tag file, you use the variable directive.
Table lists the variable directive attributes. Defines an EL variable to be used in the page invoking this tag. Either name-given or name-from-attribute must be specified. If name-given is specified, the value is the name of the variable. If name-from-attribute is specified, the value is the name of an attribute whose translation-time value at the start of the tag invocation will give the name of the variable.
If the value of a name-given attribute of a variable directive is equal to the value of a name attribute of an attribute directive or the value of a dynamic-attributes attribute of a tag directive. Defines a variable, local to the tag file, to hold the value of the EL variable.
The container will synchronize this value with the variable whose name is given in name-from-attribute. Required when name-from-attribute is specified. A translation error results if used without name-from-attribute.
A translation error results if the value of alias is the same as the value of a name attribute of an attribute directive or the name-given attribute of a variable directive. The web container handles the synchronization of variables between a tag file and a calling page. If name-given is used to specify the variable name, then the name of the variable in the calling page and the name of the variable in the tag file are the same and are equal to the value of name-given. The name-from-attribute and alias attributes of the variable directive can be used to customize the name of the variable in the calling page while another name is used in the tag file.
When using these attributes, you set the name of the variable in the calling page from the value of name-from-attribute at the time the tag was called. The name of the corresponding variable in the tag file is the value of alias. The following examples illustrate how variable synchronization works between a tag file and its calling page. The tag sets the variable to 2 , and this value is passed to the calling page before the body is invoked.
Because the scope is NESTED and because the calling page also had a variable named x , its original value, 1 , is restored when the tag completes. The body of the tag is not affected. The name of the variable is specified by the value of the attribute var.
The variable is referenced by a local name, result , in the tag file. When a tag file is executed, the web container passes it two types of fragments: fragment attributes and the tag body.
Recall from the discussion of fragment attributes that fragments are evaluated by the tag handler as opposed to the web container. Within a tag file, you use the jsp:invoke element to evaluate a fragment attribute and use the jsp:doBody element to evaluate a tag file body. The result of evaluating either type of fragment is sent to the response or is stored in an EL variable for later manipulation.
To store the result of evaluating a fragment to an EL variable, you specify the var or varReader attribute. If var is specified, the container stores the result in an EL variable of type String with the name specified by var. If varReader is specified, the container stores the result in an EL variable of type java.
Reader , with the name specified by varReader. The Reader object can then be passed to a custom tag for further processing. A translation error occurs if both var and varReader are specified. An optional scope attribute indicates the scope of the resulting variable. The possible values are page default , request , session , or application.
A translation error occurs if you use this attribute without specifying the var or varReader attribute. The tag generates the date of a book order according to the type of shipping requested. From the number of days, the tag computes the ship date. This means the script is executed as soon as it's downloaded, without blocking the browser in the meantime.
Scripts with the defer attribute are executed in order i. This also does not block the browser. If you need to support those browsers, please read this first! The current state-of-the-art is to put scripts in the tag and use the async or defer attributes.
This allows your scripts to be downloaded asap without blocking your browser. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Ask Question. Asked 6 years, 4 months ago. Active 6 years, 4 months ago. Viewed 11k times. Display the output to the end user we no need to write out. The expression tag converts everything into String object. The expression tag in JSP is used to display the output of the variables or methods or plain text.
Data within the expression tag always treated as string type only. This expression tag is a short form of out. This is a guide to JSP Expression.
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