What are the script elements of jsp

Script elements are the most frequently used elements in JSP. Java code can be embedded into HTML pages through JSP scripts; there are three script elements in JSP pages, namely "statement", "small script" and "expression".

The Scriptlet element is the most frequently used element in JSP. Java code can be embedded into HTML pages through JSP scripts. All executable Java code is executed through JSP scripts.

There are three types of script elements in JSP pages, namely: declaration, small script and expression. The following article will introduce you to these three script elements in JSP. I hope it will be helpful to you.

JSP declaration statement

JSP declaration statement is used to declare variables and define methods in JSP pages. A declaration is a tag starting with <%! and ending with %>, which can contain any number of legal Java declaration statements.

The syntax format of the JSP declaration statement is:

<%!  变量或方法定义  %>

The method declared in the JSP declaration statement is valid within the entire JSP page. Variables declared using JSP declaration statements will be converted into member variables in the Servletl class in the future (it is only initialized once when the Servlet instance is created, and will exist until the Servlet instance is destroyed, which is equivalent to a static variable); declared using JSP declaration statements The method will be converted into a member method in the Servletl class in the future. When the method is called, the variables defined in the method are allocated memory, and the memory occupied can be released after the call is completed.

Example: A variable and a method are declared in a tag:

<%!
String color[] = {"red", "green", "blue"};
String getColor(int i){
return color[i];
}
%>

JSP small script

Scriptlets (scriptlets) are Java code snippets embedded in JSP pages. A scriptlet is a tag that starts with <% and ends with %>.

The variables declared in the JSP script are local variables of the JSP page. When the JSP script is called, memory space will be allocated for the local variables. When the call is completed, the memory space occupied by the local variables will be released.

The syntax format of the JSP script is:

<% java代码?%>

The JSP script can contain variables, methods, expressions, etc.

The small script is executed every time the page is accessed, so the count variable is incremented by 1 on each request. Since the small script can contain any Java code, it is usually used to embed calculation logic in JSP pages. . At the same time, you can also use a small script to print HTML template text.

JSP expression

JSP expression (expression) exists in the expression output, which is A tag starting with <%= and ending with %>, which serves as a placeholder for Java language expressions.

The syntax format of JSP expressions:

<%= 表达式%>

The expression is evaluated every time the page is accessed, and then its value is embedded in the HTML output. Unlike variable declarations, expressions cannot end with a semicolon.

Use expressions to output any object or value of any basic data type to the output stream, or to print the value returned by any arithmetic expression, Boolean expression, or method call.

Note: <%= is a symbol, there should be no spaces in the middle.

Example:

<!-- JSP声明 -->
<%!
    String str="JSP example";
%>
<!-- JSP表达式 -->
<%=str %>

Output result:

JSP example

Recommended related video tutorials: "JSP Tutorial", "Java Tutorial 》

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