对于最新的稳定版本，请使用 Spring Framework 7.0.6!spring-doc.cadn.net.cn

变量

您可以通过使用 #variableName 语法在表达式中引用变量。变量是通过在 EvaluationContext 实现中使用 setVariable() 方法来设置的。spring-doc.cadn.net.cn

变量名必须以字母（如下定义）、下划线或美元符号开头。spring-doc.cadn.net.cn

变量名必须由一个或多个以下支持类型的字符组成。spring-doc.cadn.net.cn

在 EvaluationContext 中设置变量或根上下文对象时，建议该变量或根上下文对象的类型为 public。spring-doc.cadn.net.cn

否则，涉及变量或根上下文对象且其类型为非公开类型的某些 SpEL 表达式可能无法求值或编译。spring-doc.cadn.net.cn

由于变量在求值上下文中与 函数 共享同一个命名空间， 因此必须注意确保变量名和函数名不发生冲突。spring-doc.cadn.net.cn

以下示例展示了如何使用变量。spring-doc.cadn.net.cn

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");

EvaluationContext context = SimpleEvaluationContext.forReadWriteDataBinding().build();
context.setVariable("newName", "Mike Tesla");

parser.parseExpression("name = #newName").getValue(context, tesla);
System.out.println(tesla.getName());  // "Mike Tesla"
val tesla = Inventor("Nikola Tesla", "Serbian")

val context = SimpleEvaluationContext.forReadWriteDataBinding().build()
context.setVariable("newName", "Mike Tesla")

parser.parseExpression("name = #newName").getValue(context, tesla)
println(tesla.name)  // "Mike Tesla"

变量 #this 和 #root

变量 #this 始终被定义并指向当前评估对象 （用于解析未资格化的引用）。变量 #root 始终 被定义并指向根上下文对象。尽管 #this 可能会随着表达式组件的评估而变化， #root 始终指的是根。spring-doc.cadn.net.cn

以下示例演示了如何将 #this 变量与 集合选择 一起使用。spring-doc.cadn.net.cn

// Create a list of prime integers.
List<Integer> primes = List.of(2, 3, 5, 7, 11, 13, 17);

// Create parser and set variable 'primes' as the list of integers.
ExpressionParser parser = new SpelExpressionParser();
EvaluationContext context = SimpleEvaluationContext.forReadWriteDataBinding().build();
context.setVariable("primes", primes);

// Select all prime numbers > 10 from the list (using selection ?{...}).
String expression = "#primes.?[#this > 10]";

// Evaluates to a list containing [11, 13, 17].
List<Integer> primesGreaterThanTen =
		parser.parseExpression(expression).getValue(context, List.class);
// Create a list of prime integers.
val primes = listOf(2, 3, 5, 7, 11, 13, 17)

// Create parser and set variable 'primes' as the list of integers.
val parser = SpelExpressionParser()
val context = SimpleEvaluationContext.forReadWriteDataBinding().build()
context.setVariable("primes", primes)

// Select all prime numbers > 10 from the list (using selection ?{...}).
val expression = "#primes.?[#this > 10]"

// Evaluates to a list containing [11, 13, 17].
val primesGreaterThanTen = parser.parseExpression(expression)
		.getValue(context) as List<Int>

以下示例展示了如何将 #this 和 #root 变量与 集合投影 结合使用。spring-doc.cadn.net.cn

// Create parser and evaluation context.
ExpressionParser parser = new SpelExpressionParser();
EvaluationContext context = SimpleEvaluationContext.forReadWriteDataBinding().build();

// Create an inventor to use as the root context object.
Inventor tesla = new Inventor("Nikola Tesla");
tesla.setInventions("Telephone repeater", "Tesla coil transformer");

// Iterate over all inventions of the Inventor referenced as the #root
// object, and generate a list of strings whose contents take the form
// "<inventor's name> invented the <invention>." (using projection !{...}).
String expression = "#root.inventions.![#root.name + ' invented the ' + #this + '.']";

// Evaluates to a list containing:
// "Nikola Tesla invented the Telephone repeater."
// "Nikola Tesla invented the Tesla coil transformer."
List<String> results = parser.parseExpression(expression)
		.getValue(context, tesla, List.class);
// Create parser and evaluation context.
val parser = SpelExpressionParser()
val context = SimpleEvaluationContext.forReadWriteDataBinding().build()

// Create an inventor to use as the root context object.
val tesla = Inventor("Nikola Tesla")
tesla.setInventions("Telephone repeater", "Tesla coil transformer")

// Iterate over all inventions of the Inventor referenced as the #root
// object, and generate a list of strings whose contents take the form
// "<inventor's name> invented the <invention>." (using projection !{...}).
val expression = "#root.inventions.![#root.name + ' invented the ' + #this + '.']"

// Evaluates to a list containing:
// "Nikola Tesla invented the Telephone repeater."
// "Nikola Tesla invented the Tesla coil transformer."
val results = parser.parseExpression(expression)
		.getValue(context, tesla, List::class.java)