变量
你可以通过使用 #variableName 语法在表达式中引用变量。变量是通过在 setVariable() 的实现中调用 EvaluationContext 方法来设置的。
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变量名必须以字母（定义如下）、下划线或美元符号开头。 变量名必须由以下一种或多种支持的字符类型组成。
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在 否则，某些涉及变量或根上下文对象（其类型为非 public 类型）的 SpEL 表达式可能会求值或编译失败。 |
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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重叠。 |
以下示例展示了如何使用变量。
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Java
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Kotlin
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"这#this和#root变量
#this 变量始终被定义，并指向当前的求值对象（所有未限定的引用都将根据该对象进行解析）。#root 变量也始终被定义，并指向根上下文对象。尽管在表达式各部分求值过程中 #this 可能会发生变化，但 #root 始终指向根对象。
以下示例展示了如何将 #this 变量与集合选择结合使用。
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Java
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Kotlin
// 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。
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Java
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Kotlin
// 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)