Question

我一直在使用动态LINQ，我想知道在Java中是否有可能做类似的事情。例如，如果我使用以下工作代码：

Stream<PoliceShooting> averageAge = peopleShot.stream().filter(t->t.getAge() != null);

有没有办法像使用动态LINQ一样使它动态化

String dynamicGetter = "t.getAge() != null"
Stream<PoliceShooting> averageAge = peopleShot.stream().filter(t->dynamicGetter);

Answer 1

根据How to convert a string to a lambda expression?中的建议，依靠Nashorn，您可以定义一种方法来根据JavaScript代码构建// save data as text file to Alluxio > rdd.saveAsTextFile("alluxio://localhost:19998/rdd1") // read data as text file from Alluxio > rdd = sc.textFile("alluxio://localhost:19998/rdd1") // save data as object file to Alluxio > rdd.saveAsObjectFile("alluxio://localhost:19998/rdd2") // read data as object file from Alluxio > rdd = sc.objectFile("alluxio://localhost:19998/rdd2")：

Predicate

，然后将其用作：

public Predicate<Object> convertJSToPredicate(String js) throws ScriptException {
    ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
    return (Predicate<Object>) engine.eval("new java.util.function.Predicate(function(t) " + js + ")");
}

当然String dynamicGetter = "t.getAge() != null"; Stream<PoliceShooting> averageAge = peopleShot.stream() .filter(convertJSToPredicate(dynamicGetter));必须是JavaScript而不是Java代码，并且可以通过变量dynamicGetter访问传入的对象。

请注意，Nashorn was deprecated in Java 11。我以为会有其他的实现方式。

Java中的动态流

1 个答案: