java 使用 Spring 表达式语言以编程方式评估 bean 表达式
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Programmatically evaluate a bean expression with Spring Expression Language
提问by Hyman
I have a simple Spring Bean Expression, which evaluates fine when I define it inside an application context file:
我有一个简单的 Spring Bean 表达式，当我在应用程序上下文文件中定义它时，它的计算结果很好：
<bean id="myConfigBean" class="com.example.myBeanConfigBean">
<property name="myProperty" value="#{ someOtherBean.getData() }"/>
</bean>
Now, I want to do the same evaluation programmatically. I have used the following code:
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();
This throws an exception:
这会引发异常：
EL1007E:(pos 22): Field or property 'someOtherBean' cannot be found on null
I guess I have to set a root object somehow that allows to the configured beans like a property. But I did not get it to work yet. Anyone, who has done this already and could give a hint?
我想我必须以某种方式设置一个根对象，以允许像属性一样配置 bean。但我还没有让它工作。任何人，谁已经这样做了并且可以给出提示？
采纳答案by Gary Russell
implement BeanFactoryAware to get a reference to the bean factory; then...
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);
EDIT
编辑
To answer the comment below. The @triggers the use of the bean factory resolver to access a bean; an alternative is to add a BeanExpressionContextAccessorto the evaluation context and use a BeanExpressionContextas the root object for the evaluation...
回答下面的评论。该@触发器使用bean工厂解析器来访问一个bean; 另一种方法是将 a 添加BeanExpressionContextAccessor到评估上下文并使用 aBeanExpressionContext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);
回答by myset
Please take a look @ https://www.mkyong.com/spring3/test-spring-el-with-expressionparser/
请看看@https ://www.mkyong.com/spring3/test-spring-el-with-expressionparser/
Sample java code
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);
}
}
