英文:
Function working with stream of string does not work with a single string?
问题
在 MyService 内部，我有以下的指令，用于生成一个以分号分隔的用户电子邮件字符串：
users.stream()
.map(UserEntity::getEmail)
.filter(mailValidator.isValid())
.collect(Collectors.joining(";"));
MailValidator 通过 Spring 被注入到了 MyService 中。以下是它的定义：
@Service
public class MailValidator {
private final Pattern mailRegex = Pattern.compile(/** 一些正则表达式 */);
public Predicate<String> isValid() {
return mailRegex.asPredicate();
}
}
一切工作正常。但上述的 MailValidator 在该用例之外似乎没有用途。
更准确地说：我可以在字符串流上使用 MailValidator。但我如何使其在一个 String 本身上工作呢？
英文:
Inside MyService, I have the following instruction that produces a semicolon-delimited string of users' emails:
users.stream()
.map(UserEntity::getEmail)
.filter(mailValidator.isValid())
.collect(Collectors.joining(";"));
MailValidator is injected to MyService using Spring. This is its definition:
@Service
public class MailValidator {
private final Pattern mailRegex = Pattern.compile(/** some regular expression */);
public Predicate<String> isValid() {
return mailRegex.asPredicate();
}
}
Everything works fine. But the above MailValidator is not useful outside that use-case, I think.
More precisely: I am able to use MailValidator on a stream of strings. How can I make it work on a String itself, though?
答案1
得分: 4
你的isValid()方法返回一个实现了Predicate接口的对象。如果你查看 Predicate 的Javadoc，它有一个test(T t)方法。你所需要做的就是在输入字符串上调用该方法。最终的代码可能如下所示：
String myStringVariable = "test";
boolean isValid = mailValidator.isValid().test(myStringVariable);
英文:
Your isValid() method returns some object that implements Predicate interface. If you check Javadocs for Predicate it has a test(T t) method. All you have to do is call that method on your input String. In the end it might look like so:
String myStringVariable = "test";
boolean isValid = mailValidator.isValid().test(myStringVariable);
答案2
得分: 3
以下是翻译好的内容：
你可以将签名更改为接受一个字符串参数并返回一个布尔值。
class MailValidator {
private final Pattern mailRegex = Pattern.compile("");
public boolean isValid(String s) {
return mailRegex.matcher(s).find();
}
}
并且你可以在流中使用方法引用来应用它：
users.stream()
.map(UserEntity::getEmail)
.filter(mailValidator::isValid)
或者如果你愿意在方法的名称上做出妥协，你可以让验证器实现 Predicate：
class MailValidator implements Predicate<String> {
private final Pattern mailRegex = Pattern.compile("");
@Override
public boolean test(String s) {
return mailRegex.matcher(s).find();
}
}
然后只需执行：
users.stream()
.map(UserEntity::getEmail)
.filter(mailValidator)
在这种情况下，你可以在其他上下文中调用：
new MailValidator().test("foo");
英文:
You can change the signature to String argument with a boolean return
class MailValidator {
private final Pattern mailRegex = Pattern.compile("");
public boolean isValid(String s) {
return mailRegex.matcher(s).find();
}
}
and use it in your stream with a method reference:
users.stream()
.map(UserEntity::getEmail)
.filter(mailValidator::isValid)
Or if you are willing to compromise on the name of the method, you can make the validator implement Predicate
class MailValidator implements Predicate<String> {
private final Pattern mailRegex = Pattern.compile("");
@Override
public boolean test(String s) {
return mailRegex.matcher(s).find();
}
}
then just do
users.stream()
.map(UserEntity::getEmail)
.filter(mailValidator)
Outside of this context, you would be able to call
new MailValidator().test("foo")
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