[英]Programmatically evaluate a bean expression with Spring Expression Language
我有一个简单的Spring Bean Expression,当我在应用程序上下文文件中定义它时,它会得到很好的评估:
<bean id="myConfigBean" class="com.example.myBeanConfigBean">
<property name="myProperty" value="#{ someOtherBean.getData() }"/>
</bean>
现在,我想以编程方式进行相同的评估。 我使用了以下代码:
final ExpressionParser parser = new SpelExpressionParser();
final TemplateParserContext templateContext = new TemplateParserContext();
Expression expression = parser.parseExpression("#{ someOtherBean.getData() }", templateContext);
final String value = (String) expression.getValue();
这引发了一个异常:
EL1007E:(pos 22): Field or property 'someOtherBean' cannot be found on null
我想我必须以某种方式设置一个根对象,允许配置的bean像属性一样。 但我还没有让它工作。 任何人,已经做过这个并且可以给出一个提示吗?
实现BeanFactoryAware以获取对bean工厂的引用; 然后...
StandardEvaluationContext context = new StandardEvaluationContext();
context.setBeanResolver(new BeanFactoryResolver(this.beanFactory));
Expression expression = parser.parseExpression("@someOtherBean.getData()");
// or "@someOtherBean.data"
final String value = expression.getValue(context, String.class);
编辑
回答下面的评论。 @
触发使用bean工厂解析器来访问bean; 另一种方法是将BeanExpressionContextAccessor
添加到评估上下文中,并使用BeanExpressionContext
作为评估的根对象...
final ExpressionParser parser = new SpelExpressionParser();
StandardEvaluationContext context = new StandardEvaluationContext();
context.setBeanResolver(new BeanFactoryResolver(beanFactory));
context.addPropertyAccessor(new BeanExpressionContextAccessor());
Expression expression = parser.parseExpression("someOtherBean.getData()");
BeanExpressionContext rootObject = new BeanExpressionContext(beanFactory, null);
...
String value = expression.getValue(context, rootObject, String.class);
请看看@ https://www.mkyong.com/spring3/test-spring-el-with-expressionparser/
示例java代码
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;
public class App {
public static void main(String[] args) {
ExpressionParser parser = new SpelExpressionParser();
//literal expressions
Expression exp = parser.parseExpression("'Hello World'");
String msg1 = exp.getValue(String.class);
System.out.println(msg1);
//method invocation
Expression exp2 = parser.parseExpression("'Hello World'.length()");
int msg2 = (Integer) exp2.getValue();
System.out.println(msg2);
//Mathematical operators
Expression exp3 = parser.parseExpression("100 * 2");
int msg3 = (Integer) exp3.getValue();
System.out.println(msg3);
//create an item object
Item item = new Item("mkyong", 100);
//test EL with item object
StandardEvaluationContext itemContext = new StandardEvaluationContext(item);
//display the value of item.name property
Expression exp4 = parser.parseExpression("name");
String msg4 = exp4.getValue(itemContext, String.class);
System.out.println(msg4);
//test if item.name == 'mkyong'
Expression exp5 = parser.parseExpression("name == 'mkyong'");
boolean msg5 = exp5.getValue(itemContext, Boolean.class);
System.out.println(msg5);
}
}
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