Kotlin和Java中的IO操作

痛定思痛。 2022-05-28 13:52 248阅读 0赞

Kotlin的特性  
1.Kotlin提供了非常多，File、Stream、Reader、Writer的拓展方法  
2.使用use拓展自动关闭资源  
3.小文件一次性读写操作  
一、首先来看看繁琐的JavaIO操作，来读取一个文件

package cn.kotliner.java.io;
    
    import java.io.*;
    
    /** * Created by wangdong * Java中的IO操作 */
    public class IO { 
        public static void main(String... args) {
            BufferedReader bufferedReader = null;
            try {
                 bufferedReader = new BufferedReader(new FileReader(new File("build.gradle")));
                String line;
                while((line = bufferedReader.readLine()) != null){
                    System.out.println(line);
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    bufferedReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

二、如果用Kotlin直接译一中的JavaIO代码

package cn.kotliner.kotlin.io
    
    import java.io.*
    
    /** * Created by wangdong * Kotlin直译Java中的IO操作 */
    fun main(args: Array<String>) {
        val file = File("build.gradle")
        val bufferedReader = BufferedReader(FileReader(file))
        var line: String
    
        while(true){
            line = bufferedReader.readLine()?:break
            println(line)
        }
        bufferedReader.close()
    }

三、使用Kotlin中use方法去改写

package cn.kotliner.kotlin.io
    
    import java.io.*
    
    /** * Created by wangdong * 使用kotlin中的use的方法改写 */
    fun main(args: Array<String>) {
        val file = File("build.gradle")
        BufferedReader(FileReader(file)).use {
            var line: String
            while(true){
                line = it.readLine()?:break
                println(line)
            }
        }
    }
    
    /** * 第十行use点进去，就可以看到use是怎么实现的 */
    /** @InlineOnly public inline fun <T : Closeable?, R> T.use(block: (T) -> R): R { var closed = false try { return block(this) } catch (e: Exception) { closed = true try { this?.close() } catch (closeException: Exception) { } throw e } finally { if (!closed) { this?.close() } } }*/

四、使用kotlin中的readlin()方法改写一下

package cn.kotliner.kotlin.io
    
    import java.io.*
    
    /** * Created by wangdong * 使用readlines（）方法改写 */
    fun main(args: Array<String>) {
        File("build.gradle").readLines().forEach(::println)
    }
    
    /** * Reads the file content as a list of lines. * * Do not use this function for huge files. * * @param charset character set to use. By default uses UTF-8 charset. * @return list of file lines. public fun File.readLines(charset: Charset = Charsets.UTF_8): List<String> { val result = ArrayList<String>() forEachLine(charset) { result.add(it); } return result }*/