Spring Expression Language 简明教程

Spring SpEL - List

SpEL 表达式支持访问列表并使用对象列表的索引。

  1. 我们也可以在 SpEL 表达式中访问嵌套列表。

以下示例显示了各种使用案例。

Example

让我们更新在 Spring SpEL - Create Project 章节创建的项目。我们添加/更新了以下文件:

  1. Employee.java − Employee class.

  2. Dept.java − Department class.

  3. MainApp.java - 要运行和测试的主应用。

以下 Employee.java 文件的内容:

package com.tutorialspoint;

public class Employee {
   private List<String> awards;
   public List<String> getAwards() {
      return awards;
   }
   public void setAwards(List<String> awards) {
      this.awards = awards;
   }
}

以下 Dept.java 文件的内容:

package com.tutorialspoint;

public class Dept {
   private List<Employee> employees;
   public List<Employee> getEmployees() {
      return employees;
   }
   public void setEmployees(List<Employee> employees) {
      this.employees = employees;
   }
}

以下 MainApp.java 文件的内容:

package com.tutorialspoint;

import java.text.ParseException;
import java.util.Arrays;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;

public class MainApp {
   public static void main(String[] args) throws ParseException {
      ExpressionParser parser = new SpelExpressionParser();
      Employee employee = new Employee();
      employee.setAwards(Arrays.asList("Star of the Month", "Champion", "Accelerator"));

      Dept dept = new Dept();
      dept.setEmployees(Arrays.asList(employee));
      EvaluationContext employeeContext = new StandardEvaluationContext(employee);

      // evaluates to "Accelerator"
      String award = parser.parseExpression("awards.get(2)").getValue(employeeContext, String.class);
      System.out.println(award);

      EvaluationContext deptContext = new StandardEvaluationContext(dept);

      // evaluates to "Champion"
      award = parser.parseExpression("employees.get(0).awards.get(1)").getValue(deptContext, String.class);
      System.out.println(award);
   }
}

Output

Accelerator
Champion