总结一些Java异常的处理原则

Java异常处理最佳实践

不要忘记关闭资源

在finally里关闭资源

public void readFile() {    FileInputStream fileInputStream = null;    File file = new File("./test.txt");    try {        fileInputStream = new FileInputStream(file);        int length;        byte[] bytes = new byte[1024];        while ((length = fileInputStream.read(bytes)) != -1) {            System.out.println(new String(bytes, 0, length));        }    } catch (FileNotFoundException e) {        logger.error("找不到文件", e);    } catch (IOException e) {        logger.error("读取文件失败", e);    } finally {        if (fileInputStream != null) {            try {                fileInputStream.close();            } catch (IOException e) {                logger.error("关闭流失败", e);            }        }    }}

用try-with-resource关闭资源

public void readFile2() {    File file = new File("./test.txt");    try(FileInputStream fileInputStream = new FileInputStream(file)) {        int length;        byte[] bytes = new byte[1024];        while ((length = fileInputStream.read(bytes)) != -1) {            System.out.println(new String(bytes, 0, length));        }    } catch (FileNotFoundException e) {        logger.error("找不到文件", e);    } catch (IOException e) {        logger.error("读取文件失败", e);    }}

使用描述性消息抛出异常

指定具体的异常

• 用NumberFormatExcepton而不是Exception,这样能更快的定位问题
• NumberFormatException 是运行时异常

public void numberFormat() {    try {        String year = "2018";        System.out.println(Integer.parseInt(year));    } catch (NumberFormatException e) { // 捕获NumberFormatExceptoin而不是Exception        logger.error("年份格式化失败", e); // 描述一下异常    }}

给异常加注释

// 自定义一个异常class NotFoundGirlFriendException extends Exception {    public NotFoundGirlFriendException(String message) {        super(message);    }}/** * * @param input * @throws NotFoundGirlFriendException input为空抛出异常 */public void doSomething(String input) throws NotFoundGirlFriendException {    if (input == null) {        throw new NotFoundGirlFriendException("出错了");    }}

优先捕获具体异常

public int getYear(String year) {    int retYear = -1;    try {        retYear = Integer.parseInt(year);    } catch (NumberFormatException e) {        logger.error("年份格式化失败", e);    } catch (IllegalArgumentException e) {        logger.error("非法参数", e);    }    return retYear;}

不要捕获Throwable

• Throwable是所有异常和错误的父类,会把error捕获
• error是那些无法恢复的jvm错误,eg:StackOverflowError和OutOfMemoryError

public void test6() {    try {    } catch (Throwable e) {    }}

不要忽略异常

public void test7() {    try {    } catch (NumberFormatException e) {        logger.error("即便你认为不可能走到这个异常,也要记录一下", e);    }}

捕获和抛出只选择一种

• 不要同时记录并抛出异常,会导致相同错误日志输出多次

public void foo() {    try {        new Long("xyz");    } catch (NumberFormatException e) {        logger.error("字符串格式化成Long失败", e);        throw e;    }}

包装异常不要丢弃原始异常

class MyBusinessException extends Exception {    public MyBusinessException(String message) {        super(message);    }    public MyBusinessException(String message, Throwable cause) {        super(message, cause);    }}public void wrapException(String id) throws MyBusinessException {    try {        System.out.println(Long.parseLong(id));    } catch(NumberFormatException e) {        throw new MyBusinessException("ID格式化失败", e);    }}

参考