37 - 异常处理各场景优化实战

2021-09-06  本文已影响0人  舍是境界

平时进行软件设计开发的时候，我们除了要保证正常情况下的逻辑运行正确之外，还需要编写大量额外的代码，来处理有可能出现的异常情况，以保证代码在任何情况下，都在我们的掌控之内，不会出现非预期的运行结果。程序的 bug 往往都出现在一些边界条件和异常情况下，所以说，异常处理得好坏直接影响了代码的健壮性。全面、合理地处理各种异常能有效减少代码 bug，也是保证代码质量的一个重要手段。

在程序出错返回什么中，我们讲解了几种异常情况的处理方式，比如返回错误码、NULL 值、空对象、异常对象。针对最常用的异常对象，我们还重点讲解了两种异常类型的应用场景，以及针对函数抛出的异常的三种处理方式：直接吞掉、原封不动地抛出和包裹成新的异常抛出。

本文结合上文中提到的优化点，对代码进行优化实战，希望对你能有帮助

重构 generate() 函数

public String generate() {
    String substrOfHostName = getLastFieldOfHostName();
    long currentTimeMillis = System.currentTimeMillis();
    String randomString = generateRandomAlphameric(8);
    String id = String.format("%s-%d-%s",
            substrOfHostName, currentTimeMillis, randomString);
    return id;
  }

public String generate() throws IdGenerationFailureException {
    String substrOfHostName = getLastFieldOfHostName();
    if (substrOfHostName == null || substrOfHostName.isEmpty()) {
      throw new IdGenerationFailureException("host name is empty.");
    }
    long currentTimeMillis = System.currentTimeMillis();
    String randomString = generateRandomAlphameric(8);
    String id = String.format("%s-%d-%s",
            substrOfHostName, currentTimeMillis, randomString);
    return id;
  }

重构 getLastFieldOfHostName() 函数

private String getLastFieldOfHostName() {
    String substrOfHostName = null;
    try {
      String hostName = InetAddress.getLocalHost().getHostName();
      substrOfHostName = getLastSubstrSplittedByDot(hostName);
    } catch (UnknownHostException e) {
      logger.warn("Failed to get the host name.", e);
    }
    return substrOfHostName;
 }

 private String getLastFieldOfHostName() throws UnknownHostException{
    String substrOfHostName = null;
    String hostName = InetAddress.getLocalHost().getHostName();
    substrOfHostName = getLastSubstrSplittedByDot(hostName);
    return substrOfHostName;
 }

public String generate() throws IdGenerationFailureException {
    String substrOfHostName = null;
    try {
      substrOfHostName = getLastFieldOfHostName();
    } catch (UnknownHostException e) {
      throw new IdGenerationFailureException("host name is empty.");
    }
    long currentTimeMillis = System.currentTimeMillis();
    String randomString = generateRandomAlphameric(8);
    String id = String.format("%s-%d-%s",
            substrOfHostName, currentTimeMillis, randomString);
    return id;
  }

重构 getLastSubstrSplittedByDot() 函数

@VisibleForTesting
  protected String getLastSubstrSplittedByDot(String hostName) {
    String[] tokens = hostName.split("\\.");
    String substrOfHostName = tokens[tokens.length - 1];
    return substrOfHostName;
  }

@VisibleForTesting
  protected String getLastSubstrSplittedByDot(String hostName) {
    if (hostName == null || hostName.isEmpty()) {
      throw IllegalArgumentException("..."); //运行时异常
    }
    String[] tokens = hostName.split("\\.");
    String substrOfHostName = tokens[tokens.length - 1];
    return substrOfHostName;
  }

private String getLastFieldOfHostName() throws UnknownHostException{
    String substrOfHostName = null;
    String hostName = InetAddress.getLocalHost().getHostName();
    if (hostName == null || hostName.isEmpty()) { // 此处做判断
      throw new UnknownHostException("...");
    }
    substrOfHostName = getLastSubstrSplittedByDot(hostName);
    return substrOfHostName;
 }

重构 generateRandomAlphameric() 函数

@VisibleForTesting
  protected String generateRandomAlphameric(int length) {
    char[] randomChars = new char[length];
    int count = 0;
    Random random = new Random();
    while (count < length) {
      int maxAscii = 'z';
      int randomAscii = random.nextInt(maxAscii);
      boolean isDigit= randomAscii >= '0' && randomAscii <= '9';
      boolean isUppercase= randomAscii >= 'A' && randomAscii <= 'Z';
      boolean isLowercase= randomAscii >= 'a' && randomAscii <= 'z';
      if (isDigit|| isUppercase || isLowercase) {
        randomChars[count] = (char) (randomAscii);
        ++count;
      }
    }
    return new String(randomChars);
  }
}

重构之后的 RandomIdGenerator 代码

public class RandomIdGenerator implements IdGenerator {
  private static final Logger logger = LoggerFactory.getLogger(RandomIdGenerator.class);
  @Override
  public String generate() throws IdGenerationFailureException {
    String substrOfHostName = null;
    try {
      substrOfHostName = getLastFieldOfHostName();
    } catch (UnknownHostException e) {
      throw new IdGenerationFailureException("...", e);
    }
    long currentTimeMillis = System.currentTimeMillis();
    String randomString = generateRandomAlphameric(8);
    String id = String.format("%s-%d-%s",
            substrOfHostName, currentTimeMillis, randomString);
    return id;
  }
  private String getLastFieldOfHostName() throws UnknownHostException{
    String substrOfHostName = null;
    String hostName = InetAddress.getLocalHost().getHostName();
    if (hostName == null || hostName.isEmpty()) {
      throw new UnknownHostException("...");
    }
    substrOfHostName = getLastSubstrSplittedByDot(hostName);
    return substrOfHostName;
  }
  @VisibleForTesting
  protected String getLastSubstrSplittedByDot(String hostName) {
    if (hostName == null || hostName.isEmpty()) {
      throw new IllegalArgumentException("...");
    }
    String[] tokens = hostName.split("\\.");
    String substrOfHostName = tokens[tokens.length - 1];
    return substrOfHostName;
  }
  @VisibleForTesting
  protected String generateRandomAlphameric(int length) {
    if (length <= 0) {
      throw new IllegalArgumentException("...");
    }
    char[] randomChars = new char[length];
    int count = 0;
    Random random = new Random();
    while (count < length) {
      int maxAscii = 'z';
      int randomAscii = random.nextInt(maxAscii);
      boolean isDigit= randomAscii >= '0' && randomAscii <= '9';
      boolean isUppercase= randomAscii >= 'A' && randomAscii <= 'Z';
      boolean isLowercase= randomAscii >= 'a' && randomAscii <= 'z';
      if (isDigit|| isUppercase || isLowercase) {
        randomChars[count] = (char) (randomAscii);
        ++count;
      }
    }
    return new String(randomChars);
  }
}

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