java - 未处理异常的看似虚假的错误消息

Question

这是代码:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.FileReader;
import java.io.BufferedReader;
import java.util.stream.Collectors;
import java.io.FileWriter;
import java.io.BufferedWriter;
import java.util.List;
public class CSVIO
{
    //read a file and return a list of records in the file
    public static List<String[]> read(File f) throws IOException
    {
        BufferedReader br = new BufferedReader(new FileReader(f));
        List<String[]> out = br.lines()
                               .map( e -> e.split(","))
                               .collect(Collectors.toList());
        return out;

    }
    //write from a list of recrords into CSV format
    public static void write(List<String[]> items, File dest) throws IOException
    {
        //return true if it successfully writes.
            final BufferedWriter bw = new BufferedWriter(new FileWriter(dest));
            items.stream()
                 .map( row -> String.join(",",  row))
                 .forEach( row  -> bw.write(row + "\n"));
    }
}

运行时收到此错误消息:

$ javac CSVIO.java
CSVIO.java:29: error: unreported exception IOException; must be caught or declared to be thrown
                 .forEach( row  -> bw.write(row + "\n"));
                                           ^
1 error

我已经正确声明 write 方法抛出异常。我有什么遗漏的吗？

Answer 1

问题是，您的 br.write() 抛出异常。您必须在 lambda 表达式中捕获这一点 (.forEach()):

items.stream()
     .map(row -> String.join(",",  row))
     .forEach( row  -> {
         try {
             bw.write(row + "\n");
         } catch (IOException e) {
             e.printStackTrace();
         }
     });

但是您可以使用 Files.write() 来缩短它:

public static void write(List<String[]> items, Path path) throws IOException {
    List<String> lines = items.stream()
            .map(row -> String.join(",", row))
            .collect(Collectors.toList());
    Files.write(path, lines);
}

您还可以使用 Files.lines() 简化您的 read 方法:

public static List<String[]> read(Path path) throws IOException {
    try (Stream<String> lines = Files.lines(path)) {
        return lines
                .map(e -> e.split(","))
                .collect(Collectors.toList());
    }
}