我知道如何创建一个有String参数并返回int的方法的引用,它是:

Function<String, Integer>

然而,如果函数抛出异常,比如它被定义为:

Integer myMethod(String s) throws IOException

我该如何定义这个引用呢?


当前回答

这并不是Java 8所特有的。你正在尝试编译一些等价的东西:

interface I {
    void m();
}
class C implements I {
    public void m() throws Exception {} //can't compile
}

其他回答

我所做的是允许用户在异常情况下给出他实际想要的值。 我有一个像这样的东西

public static <T, R> Function<? super T, ? extends R> defaultIfThrows(FunctionThatThrows<? super T, ? extends R> delegate, R defaultValue) {
    return x -> {
        try {
            return delegate.apply(x);
        } catch (Throwable throwable) {
            return defaultValue;
        }
    };
}

@FunctionalInterface
public interface FunctionThatThrows<T, R> {
    R apply(T t) throws Throwable;
}

这个可以被称为:

defaultIfThrows(child -> child.getID(), null)
public void frankTest() {
    int pageId= -1;

    List<Book> users= null;
    try {
        //Does Not Compile:  Object page=DatabaseConnection.getSpringConnection().queryForObject("SELECT * FROM bookmark_page", (rw, n) -> new Portal(rw.getInt("id"), "", users.parallelStream().filter(uu -> uu.getVbid() == rw.getString("user_id")).findFirst().get(), rw.getString("name")));

        //Compiles:
        Object page= DatabaseConnection.getSpringConnection().queryForObject("SELECT * FROM bookmark_page", (rw, n) -> { 
            try {
                final Book bk= users.stream().filter(bp -> { 
                    String name= null;
                    try {
                        name = rw.getString("name");
                    } catch (Exception e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    return bp.getTitle().equals(name); 
                }).limit(1).collect(Collectors.toList()).get(0);
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return new Portal(rw.getInt("id"), "", users.get(0), rw.getString("name")); 
        } );
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

对我来说,首选的解决方案是使用Lombok。这是一个很好的图书馆。

而不是:

Integer myMethod(String s) throws IOException

你会有

import lombok.SneakyThrows;

@SneakyThrows
Integer myMethod(String s)

异常仍然被抛出,但您不需要使用throws声明它。

使用Jool库或JOOQ中的jOOλ库。它不仅提供了未经检查的异常处理接口,还为Seq类提供了许多有用的方法。

此外,它包含多达16个参数的功能接口。此外,它还提供了用于不同场景的Tuple类。

乔尔去链接

特别是在org.jooq.lambda.fi.util.function包的库查找中。它包含Java-8中所有带有前置Checked的接口。参考如下:-

然而,你可以创建自己的FunctionalInterface,抛出如下..

@FunctionalInterface
public interface UseInstance<T, X extends Throwable> {
  void accept(T instance) throws X;
}

然后使用Lambdas或引用实现它,如下所示。

import java.io.FileWriter;
import java.io.IOException;

//lambda expressions and the execute around method (EAM) pattern to
//manage resources

public class FileWriterEAM  {
  private final FileWriter writer;

  private FileWriterEAM(final String fileName) throws IOException {
    writer = new FileWriter(fileName);
  }
  private void close() throws IOException {
    System.out.println("close called automatically...");
    writer.close();
  }
  public void writeStuff(final String message) throws IOException {
    writer.write(message);
  }
  //...

  public static void use(final String fileName, final UseInstance<FileWriterEAM, IOException> block) throws IOException {

    final FileWriterEAM writerEAM = new FileWriterEAM(fileName);    
    try {
      block.accept(writerEAM);
    } finally {
      writerEAM.close();
    }
  }

  public static void main(final String[] args) throws IOException {

    FileWriterEAM.use("eam.txt", writerEAM -> writerEAM.writeStuff("sweet"));

    FileWriterEAM.use("eam2.txt", writerEAM -> {
        writerEAM.writeStuff("how");
        writerEAM.writeStuff("sweet");      
      });

    FileWriterEAM.use("eam3.txt", FileWriterEAM::writeIt);     

  }


 void writeIt() throws IOException{
     this.writeStuff("How ");
     this.writeStuff("sweet ");
     this.writeStuff("it is");

 }

}