Expression Language 3.0 API and Java -class library integrated guidelines
Expression Language (EL) is a simple and powerful mechanism for dynamic access and operation of Java objects.EL's latest version is 3.0. There are many new features and APIs in this version, making it more closely integrated with the Java class library.
This article will introduce how to integrate the EL 3.0 API and Java class libraries to provide you with steps and example code.
1. Add EL 3.0 dependency library
First, you need to add EL 3.0 to your Java project.You can use Maven and other construction tools to automatically manage dependency relationships, or manually add the required jar files to your project.
The following is an example POM.XML file that adds EL 3.0 dependencies in the Maven project:
<dependencies>
<dependency>
<groupId>javax.el</groupId>
<artifactId>javax.el-api</artifactId>
<version>3.0.0</version>
</dependency>
<dependency>
<groupId>org.glassfish</groupId>
<artifactId>javax.el</artifactId>
<version>3.0.0</version>
</dependency>
</dependencies>
Please ensure that these dependencies are correctly downloaded and included in the project when constructing projects.
2. Configure EL parser
In your Java code, interact with EL 3.0 by creating an EL parser.The parser is responsible for parsing and executing expressions.
The following is an example code that creates EL parsers:
import javax.el.*;
ELResolver resolver = new CompositeELResolver();
ELContext context = new ELContextImpl(resolver);
ExpressionFactory factory = new ExpressionFactoryImpl();
ELParser parser = new ELParser(new ELManager());
ELProcessor processor = new ELProcessor();
processor.setExpressionFactory(factory);
processor.setELManager(manager);
processor.defineBean("myBean", new MyBean());
In this example, we created an EL parser and configured a parser parser, EL context, expression factory and EL processor.We also use the Definebean method to define a custom Java Bean called "Mybean".
Third, use EL expression
Once the EL parser is configured correctly, and your Java object and method can be accessed through EL expressions, you can use EL expressions to dynamically access and operate your Java object.
The following is an example code using EL expression:
ValueExpression expression = factory.createValueExpression(context, "${myBean.property}", String.class);
String propertyValue = (String) expression.getValue(context);
MethodExpression method = factory.createMethodExpression(context, "${myBean.method}", Void.TYPE, new Class[]{});
method.invoke(context, null);
In this example, we first created a value expression using an expression factory to obtain the value of the attribute called "Property".We then use the GetValue method of this expression to obtain the value of the attribute.
Next, we used an expression factory to create a method expression to call the method called "Method".Finally, we use the Invoke method of this expression to call the method.
Through the above steps and sample code, you can integrate EL 3.0 API with the Java library to achieve the function of dynamic access and operation of the Java object.Hope this article will help you!
