Jakarta expression language API in the development of java library: Tips and experience sharing
Jakarta expression language (EL) is an expression language used in Java Web applications.In the development of the Java library, we often need to use EL to simplify and optimize our code.This article will share some techniques and experiences using Jakarta El, and provide some complete programming code and related configuration descriptions.
1. Learn Jakarta El
Jakarta El is part of the Java Enterprise Edition (Javaee), which provides a way to use expression in JSP, JSF and other Javaee technology.Use EL to calculate and analyze expressions during runtime, so that programs have higher flexibility and maintenance.
Second, configure Jakarta EL
1. Import dependencies
Use Jakarta El to add the corresponding library to the project's dependence.In the Maven project, the following dependencies can be added to the pom.xml file:
<dependency>
<groupId>jakarta.el</groupId>
<artifactId>jakarta.el-api</artifactId>
<version>3.0.3</version>
</dependency>
<dependency>
<groupId>org.glassfish</groupId>
<artifactId>jakarta.el</artifactId>
<version>3.0.3</version>
</dependency>
2. Configure web.xml
In the web.xml file, you need to add the following configuration to enable Jakarta El:
<jsp-config>
<jsp-property-group>
<url-pattern>*.jsp</url-pattern>
<el-ignored>false</el-ignored>
</jsp-property-group>
</jsp-config>
Third, Jakarta EL's use skills and experience sharing
1. Use EL in JSP
In the JSP page, we can use EL expressions to access and display data.For example, you can get the name of the variable named "User" through `$ {user.name}`.
2. Use EL in JSF
In Javaseerver Faces (JSF), EL can be used to operate and present component attributes.For example, through the `#{userBean.name}`, you can get the attribute value of the JSF management bean named "userbean".
3. Access collection and array
With EL, we can easily access the elements in the collection and array.For example, the name of the first element in the set of the first element named "UserList" through `$ {userlist [0] .name}`.
4. EL operator
Jakarta El provides rich operators that can be used to calculate and compare expressions.For example, `$ {(user.age> 18)? ':': 'Jelly"} `can display the corresponding text according to the age of the" user "object.
5. Custom EL function and variables
We can customize the EL function and variables for use in expressions.For example, through the implementation class of the `FunctionMapper` interface, you can register a custom EL function.
6. Safety consideration
When using EL, we should consider security issues to prevent XSS attacks.You can enhance the security of EL expression by setting proper context initialization parameters.
Fourth, complete programming code example
Below is a simple example, demonstrating how to use Jakarta El on the JSP page:
index.jsp:
html
<!DOCTYPE html>
<html>
<head>
<title>Jakarta EL Example</title>
</head>
<body>
<h1>Welcome to Jakarta EL Example</h1>
<p>Current time: ${new java.util.Date()}</p>
</body>
</html>
After opening the above JSP page in the browser, the current time will be displayed.
The above is the technique and experience of Jakarta El in the development of Java libraries.Through in -depth understanding and use of Jakarta El, we can improve efficiency and code quality during the development process.I hope this article will help you!
