设计模式之美-课程笔记22-编程规范&代码质量实战（ID生成器）

public class IdGenerator {
  private static final Logger logger = LoggerFactory.getLogger(IdGenerator.class);

  public static String generate() {
    String id = "";
    try {
      String hostName = InetAddress.getLocalHost().getHostName();
      String[] tokens = hostName.split("\\.");
      if (tokens.length > 0) {
        hostName = tokens[tokens.length - 1];
      }
      char[] randomChars = new char[8];
      int count = 0;
      Random random = new Random();
      while (count < 8) {
        int randomAscii = random.nextInt(122);
        if (randomAscii >= 48 && randomAscii <= 57) {
          randomChars[count] = (char)('0' + (randomAscii - 48));
          count++;
        } else if (randomAscii >= 65 && randomAscii <= 90) {
          randomChars[count] = (char)('A' + (randomAscii - 65));
          count++;
        } else if (randomAscii >= 97 && randomAscii <= 122) {
          randomChars[count] = (char)('a' + (randomAscii - 97));
          count++;
        }
      }
      id = String.format("%s-%d-%s", hostName,
              System.currentTimeMillis(), new String(randomChars));
    } catch (UnknownHostException e) {
      logger.warn("Failed to get the host name.", e);
    }

    return id;
  }
}

package IDGenerator;

import java.net.UnknownHostException;

/**
 * Created by szhang on 2023/7/23
 */
public interface IdGenerator {
    String generate() throws UnknownHostException;
}


package IDGenerator;

import com.sun.org.slf4j.internal.Logger;
import com.sun.org.slf4j.internal.LoggerFactory;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Objects;
import java.util.Random;

/**
 * Created by szhang on 2023/7/23
 */

public class IdGeneratorImpl implements IdGenerator {
    private static final Logger logger = LoggerFactory.getLogger(IdGeneratorV0Impl.class);
    private static final int RANDOM_CHAR_LENGTH = 8;

    @Override
    public String generate() throws UnknownHostException {
        String id;
        try {
            String hostStr = getHostName();
            if (Objects.isNull(hostStr)) {
                throw new UnknownHostException();
            }
            id = String.format("%s-%d-%s", hostStr, System.currentTimeMillis(), generateAlphabaticRandomChars());
        } catch (UnknownHostException e) {
            logger.warn("Failed to get the host name.", e);
            throw e;
        }

        return id;
    }

    private String generateAlphabaticRandomChars() {
        StringBuilder sb = new StringBuilder();
        Random random = new Random();
        char[] availableChars = new char[]{'0', '1', '2', 'a', 'b', 'A', 'B'}; // 0-9, a-z, A-Z;
        for (int i = 0; i < RANDOM_CHAR_LENGTH; i++) {
            int randomAscii = random.nextInt(availableChars.length);
            sb.append(availableChars[randomAscii]);
        }
        return sb.toString();
    }

    private String getHostName() throws UnknownHostException {
        String hostName = InetAddress.getLocalHost().getHostName();
        String[] tokens = hostName.split("\\.");
        if (tokens.length > 0) {
           return tokens[tokens.length - 1];
        }
        return null;
    }
}

IdGenearator idGenerator = new LogTraceIdGenerator();
替换为:
IdGenearator idGenerator = new UserIdGenerator();

public interface IdGenerator {
  String generate();
}

public interface LogTraceIdGenerator extends IdGenerator {
}

public class RandomIdGenerator implements LogTraceIdGenerator {
  private static final Logger logger = LoggerFactory.getLogger(RandomIdGenerator.class);

  @Override
  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;
  }

  private String getLastfieldOfHostName() {
    String substrOfHostName = null;
    try {
      String hostName = InetAddress.getLocalHost().getHostName();
      String[] tokens = hostName.split("\\.");
      substrOfHostName = tokens[tokens.length - 1];
      return substrOfHostName;
    } catch (UnknownHostException e) {
      logger.warn("Failed to get the host name.", e);
    }
    return substrOfHostName;
  }

  private 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);
  }
}

//代码使用举例
LogTraceIdGenerator logTraceIdGenerator = new RandomIdGenerator();

public String generate();
private String getLastfieldOfHostName();
@VisibleForTesting
protected String getLastSubstrSplittedByDot(String hostName);
@VisibleForTesting
protected String generateRandomAlphameric(int length);

public class RandomIdGeneratorTest {
  @Test
  public void testGetLastSubstrSplittedByDot() {
    RandomIdGenerator idGenerator = new RandomIdGenerator();
    String actualSubstr = idGenerator.getLastSubstrSplittedByDot("field1.field2.field3");
    Assert.assertEquals("field3", actualSubstr);

    actualSubstr = idGenerator.getLastSubstrSplittedByDot("field1");
    Assert.assertEquals("field1", actualSubstr);

    actualSubstr = idGenerator.getLastSubstrSplittedByDot("field1#field2#field3");
    Assert.assertEquals("field1#field2#field3", actualSubstr);
  }

  // 此单元测试会失败，因为我们在代码中没有处理hostName为null或空字符串的情况
  // 这部分优化留在第36、37节课中讲解
  @Test
  public void testGetLastSubstrSplittedByDot_nullOrEmpty() {
    RandomIdGenerator idGenerator = new RandomIdGenerator();
    String actualSubstr = idGenerator.getLastSubstrSplittedByDot(null);
    Assert.assertNull(actualSubstr);

    actualSubstr = idGenerator.getLastSubstrSplittedByDot("");
    Assert.assertEquals("", actualSubstr);
  }

  @Test
  public void testGenerateRandomAlphameric() {
    RandomIdGenerator idGenerator = new RandomIdGenerator();
    String actualRandomString = idGenerator.generateRandomAlphameric(6);
    Assert.assertNotNull(actualRandomString);
    Assert.assertEquals(6, actualRandomString.length());
    for (char c : actualRandomString.toCharArray()) {
         Assert.assertTrue(('0' <= c && c <= '9') || ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z'));
    }
  }

  // 此单元测试会失败，因为我们在代码中没有处理length<=0的情况
  // 这部分优化留在第36、37节课中讲解
  @Test
  public void testGenerateRandomAlphameric_lengthEqualsOrLessThanZero() {
    RandomIdGenerator idGenerator = new RandomIdGenerator();
    String actualRandomString = idGenerator.generateRandomAlphameric(0);
    Assert.assertEquals("", actualRandomString);

    actualRandomString = idGenerator.generateRandomAlphameric(-1);
    Assert.assertNull(actualRandomString);
  }
}

/**
 * Id Generator that is used to generate random IDs.
 *
 * <p>
 * The IDs generated by this class are not absolutely unique,
 * but the probability of duplication is very low.
 */
public class RandomIdGenerator implements LogTraceIdGenerator {
  private static final Logger logger = LoggerFactory.getLogger(RandomIdGenerator.class);

  /**
   * Generate the random ID. The IDs may be duplicated only in extreme situation.
   *
   * @return an random ID
   */
  @Override
  public String generate() {
    //...
  }

  /**
   * Get the local hostname and
   * extract the last field of the name string splitted by delimiter '.'.
   *
   * @return the last field of hostname. Returns null if hostname is not obtained.
   */
  private String getLastfieldOfHostName() {
    //...
  }

  /**
   * Get the last field of {@hostName} splitted by delemiter '.'.
   *
   * @param hostName should not be null
   * @return the last field of {@hostName}. Returns empty string if {@hostName} is empty string.
   */
  @VisibleForTesting
  protected String getLastSubstrSplittedByDot(String hostName) {
    //...
  }

  /**
   * Generate random string which
   * only contains digits, uppercase letters and lowercase letters.
   *
   * @param length should not be less than 0
   * @return the random string. Returns empty string if {@length} is 0
   */
  @VisibleForTesting
  protected String generateRandomAlphameric(int length) {
    //...
  }
}