Kotlin 异常处理

1. kotlin 捕获异常

• 不论在 try 块、catch 块中执行怎样的代码（除非退出虚拟机 System.exit(1) ），finally 块的代码总会被执行

// 定义顶级常量
const val fileName = "src/com/william/testkt/exception_demo.txt"

/**
 * 写入文件，使用 try-catch 捕获异常
 */
fun writeFile(src: String): Int {
     
    var fos: FileOutputStream? = null
    try {
     
        val file = File(fileName)
        fos = FileOutputStream(file)
        fos.write(src.toByteArray())
        return 1 // 会被 finally 块中的代码覆盖
    } catch (e: Exception) {
     
        e.printStackTrace()
        return 2 // 会被 finally 块中的代码覆盖
    } finally {
     
        fos?.close()
        return 3
    }
}

/**
 * 读取文件
 */
fun readFile(): String {
     
    var fis: FileInputStream? = null
    try {
     
        val file = File(fileName)
        val size = file.length().toInt()
        fis = FileInputStream(file)
        val sb = StringBuilder()
        val buffer = ByteArray(size)
        fis.read(buffer)
        sb.append(String(buffer))
        return sb.toString()
    } catch (e: Exception) {
     
        e.printStackTrace() // 打印堆栈信息
        return "${
       e.message}"
    } finally {
     
        println("finally")
        fis?.close()
    }
}

fun main() {
     
    val result = writeFile("this is a simple message")
    println(result) // 3

    val text = readFile()
    println(text)
}

2. kotlin 先处理小异常，再处理大异常

fun compute(obj: String?) {
     
    try {
     
        Integer.parseInt(obj)
    } catch (e: RuntimeException) {
     
        println("RuntimeException: ${
       e.message}")
    } catch (e: Exception) {
     
        println("Exception: ${
       e.message}")
    }
}

3. kotlin 使用 throw 抛出异常

fun throwExFun(param: String?) {
     
    if (param == null) {
     
        throw NullPointerException()
    }
}

4. kotlin 自定义异常

class CustomException : Exception {
     
    // 无参构造
    constructor() {
     }

    // 带参构造
    constructor(msg: String) : super(msg) {
     }
}

fun throwCustomExFun(param: String?) {
     
    if (param == null) {
     
 		// 使用 throw 抛出自定义异常
        throw CustomException("param is null")
    }
}

附 Github 源码：

TestException.kt