Java常用 工具类

自上而下工具类为

• 集合工具类
• 文件工具类
• 随机字符串生成器
• String工具类

集合操作日常工具

import java.lang.reflect.Array;
import java.util.*;
import java.util.function.Function;

/**
 * 集合操作日常工具
 */
public class CollectionUtils {

    public static final Function ASSIGN = new Function() {
        @Override
        public Object apply(Object o) {
            return o;
        }
    };

    public static <T> List<T> copyList(Collection<T> input) {
        return convertList(input, new Function<T, T>() {
            @Override
            public T apply(T o) {
                return o;
            }
        });
    }

    /**
     * 复制并转换List
     *
     * @param input
     * @param converter
     * @param <T1>
     * @param <T2>
     * @return
     */
    public static <T1, T2> List<T2> convertList(Collection<T1> input, Function<T1, T2> converter) {
        List<T2> result = new ArrayList<T2>();
        if (input == null) {
            return result;
        }
        for (T1 a : input) {
            T2 a2 = converter.apply(a);
            if (a2 != null) {
                result.add(a2);
            }
        }
        return result;
    }

    /**
     * @param input
     * @param convertor
     * @param <T1>
     * @param <T2>
     * @return
     */
    public static <T1, T2> List<T2> convertList(T1[] input, Function<T1, T2> convertor) {
        List<T2> result = new ArrayList<T2>();
        if (input == null) {
            return result;
        }
        for (T1 a : input) {
            T2 a2 = convertor.apply(a);
            if (a2 != null) {
                result.add(a2);
            }
        }
        return result;
    }

    /**
     * 转换数组
     *
     * @param input
     * @param convertor
     * @param <T1>
     * @param <T2>
     * @return
     */
    public static <T1, T2> T2[] convertArray(T1[] input, Function<T1, T2> convertor) {
        if (input == null || input.length == 0) {
            return null;
        }
        List<T2> result = new ArrayList<T2>();
        for (T1 v : input) {
            result.add(convertor.apply(v));
        }

        if (result.size() == 0) {
            return null;
        }
        T2[] r = (T2[]) Array.newInstance(result.get(0).getClass(), result.size());
        result.toArray(r);
        return r;
    }

    /**
     * 单纯的复制map
     *
     * @param input
     * @param <K>
     * @param <V>
     * @return
     */
    public static <K, V> Map<K, V> copyMap(Map<K, V> input) {
        return convertMapValues(input, new Function<V, V>() {
            @Override
            public V apply(V o) {
                return o;
            }
        });
    }

    /**
     * 复制并转换Map
     *
     * @param input
     * @param convertor
     * @param <K>
     * @param <V1>
     * @param <V2>
     * @return
     */
    public static <K, V1, V2> Map<K, V2> convertMapValues(Map<K, V1> input, Function<V1, V2> convertor) {
        Map<K, V2> result = new HashMap<K, V2>();
        if (input == null) {
            return result;
        }
        for (Map.Entry<K, V1> e : input.entrySet()) {
            result.put(e.getKey(), convertor.apply(e.getValue()));
        }
        return result;
    }

    /**
     * 合并两组Keys
     *
     * @param set1
     * @param set2
     * @param <K>
     * @return
     */
    public static <K> Collection<K> mergeKeys(Collection<K> set1, Collection<K> set2) {
        HashSet<K> keys = new HashSet<K>();
        for (K k : set1) {
            keys.add(k);
        }
        for (K k : set2) {
            keys.add(k);
        }
        return keys;
    }

    /***
     * 排序
     * @param list
     * @param <E>
     * @return
     */
    public static <E extends Comparable<E>> Collection<E> sortList(Collection<E> list) {
        List<E> result = CollectionUtils.convertList(list, new Function<E, E>() {
            @Override
            public E apply(E e) {
                return e;
            }
        });

        result.sort(new Comparator<E>() {
            @Override
            public int compare(E e, E o) {
                return e.compareTo(o);
            }
        });
        return result;
    }

    /**
     * 合并数组元素
     *
     * @param array
     * @param elements
     * @param <E>
     * @return
     */
    public static <E> E[] mergeArray(E[] array, E... elements) {
        List<E> list = new ArrayList<E>();
        if (array != null) {
            for (E a : array) {
                list.add(a);
            }
        }
        for (E a : elements) {
            if (a != null) {
                list.add(a);
            }
        }

        if (list.size() == 0) {
            return array;
        } else {
            E[] result = (E[]) Array.newInstance(list.get(0).getClass(), list.size());
            list.toArray(result);
            return result;
        }
    }

	/**
	 * 转为','分割的字符串
	 * @param objects
	 * @param <E>
	 * @return
	 */
    public static <E> String toString(Iterable<E> objects) {
        if (objects == null) {
            return "[]";
        }
        StringBuilder str = new StringBuilder();
        for (Object o : objects) {
            str.append(o != null ? o.toString() : "").append(",");
        }
        if (str.length() > 0) {
            return str.substring(0, str.length() - 1);
        } else {
            return "";
        }
    }
}

文件操作工具类

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.*;
import java.lang.management.ManagementFactory;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 * 文件相关帮助类
 */
public class FileUtils {
	private static final Logger LOGGER = LoggerFactory.getLogger(FileUtils.class);
	/**
	 * 将当前的pid写入到文件中
	 * @param filename
	 */
	public static void writeCurrentPid(String filename) {
		String name = ManagementFactory.getRuntimeMXBean().getName();
		System.out.println(name);
		String pid = name.split("@")[0];
		try {
			FileOutputStream fs = new FileOutputStream(filename, false);
			fs.write(pid.getBytes());
			fs.close();
		} catch (Exception ex) {
			ex.printStackTrace();
		}
	}
	/**
	 * 重命名文件
	 * @param oldFile
	 * @param newFile
	 * @throws IOException
	 */
	public static boolean renameFile(String oldFile, String newFile) throws IOException {
		File file = new File(oldFile);
		File file2 = new File(newFile);

		if (file2.exists()) {
			throw new IOException("file exists:" + newFile);
		}

		boolean success = file.renameTo(file2);
		LOGGER.info("<<<FILE>>> rename file from {} to {} success={}", oldFile, newFile, success);
		return success;
	}

	/**
	 * 从文件中读取
	 * @param filename
	 * @return
	 */
	public static String readFromFile(String filename, String encoding) {
		Path path = Paths.get(filename);
		try {
			byte[] buffer = Files.readAllBytes(path);
			return new String(buffer, encoding);
		} catch (IOException e) {
			throw new IllegalArgumentException("readFromFile failed:" + filename, e);
		}
	}

	/**
	 * 从文件中读取
	 * @param filename
	 * @return
	 */
	public static byte[] readFromFile(String filename) {
		Path path = Paths.get(filename);
		try {
			byte[] buffer = Files.readAllBytes(path);
			return buffer;
		} catch (IOException e) {
			throw new IllegalArgumentException("readFromFile failed:" + filename, e);
		}
	}

	/**
	 *
	 * @param stream
	 * @return
	 */
	public static String readFromStream(InputStream stream) {
		return readFromStream(stream, "UTF-8");
	}

	/**
	 * 从InputStream中按
	 * @param stream
	 * @return
	 */
	public static String readFromStream(InputStream stream, String encoding) {
		try {
			ByteArrayOutputStream arr = new ByteArrayOutputStream();
			byte[] buffer = new byte[8192];
			while (true) {
				int len = stream.read(buffer);
				if (len > 0) {
					arr.write(buffer, 0, len);
				} else {
					break;
				}
			}
			return new String(arr.toByteArray(), encoding);
		} catch (Exception ex) {
			throw new RuntimeException("readStream failed", ex);
		}
	}

	/**
	 * 写文件
	 * @param name
	 * @param content
	 * @throws IOException
	 */
	public static void writeFile(String name, String content) throws IOException {
		LOGGER.info("<<<FILE>>> write file {}", name);
		FileWriter writer = new FileWriter(name, false);
		BufferedWriter out = new BufferedWriter(writer);
		out.write(content);
		out.close();
	}

	/**
	 * 删除文件, 文件不存在返回false, 删除失败抛异常
	 *
	 * @param name
	 * @return
	 */
	public static boolean deleteFile(String name) {
		File file = new File(name);
		if (!file.exists()) {
			LOGGER.info("<<<FILE>>> delete file {} NOT EXISTS", name);
			return false;
		}

		boolean success = file.delete();
		LOGGER.info("<<<FILE>>> delete file {} success={}", name, success);
		return success;
	}

	public static void mkdir(String s) {
		File f = new File(s);
		if (!f.exists()) {
			f.mkdir();
			LOGGER.info("<<<FILE>>> mkdir {}", s);
		} else if (!f.isDirectory()) {
			LOGGER.info("<<<FILE>>> mkdir {} failed, type conflicted", s);
			throw new IllegalArgumentException("path already exists" + s);
		}
	}
}

随机字符串生成器

public class StringGenerator {
	public static int MAX_RETRYS = 200;

	public static String LOWERCASE_CHARS = "abcdefghijklmnopqrstuvwxyz";
	public static String UPPERCASE_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	public static String NUMBERS = "0123456789";
	public static String SPECIALS = ".:+=^!/*?&<>()[]{}@%#";

	public static String BASIC = LOWERCASE_CHARS + NUMBERS;
	public static String WITH_UPPERCASE = BASIC + UPPERCASE_CHARS;
	public static String WITH_SPECIALS = WITH_UPPERCASE + SPECIALS;

	public static Random RANDOM = new Random(System.currentTimeMillis());

	public static String generate(int length) {
		return generate(BASIC, length, true, true, false, false);
	}

	public static String generateWithUppercase(int length) {
		return generate(WITH_UPPERCASE, length, true, true, true, false);
	}

	public static String generateWithSpecial(int length) {
		return generate(WITH_SPECIALS, length, true, true, true, true);
	}


	private static String generate(String chars, int length, boolean lower, boolean numbers, boolean upper, boolean specials) {
		for (int k = 0; k < MAX_RETRYS; k++) {
			StringBuilder str = new StringBuilder();
			for (int i = 0; i < length; i++) {
				str.append(chars.charAt(RANDOM.nextInt(chars.length())));
			}
			String s = str.toString();
			if (test(s, lower, numbers, upper, specials)) {
				return s;
			}
		}
		throw new RuntimeException("Over max generator retrys");
	}

	private static boolean test(String s, boolean lower, boolean numbers, boolean upper, boolean specials) {
		for (int i = 0; i < s.length(); i++) {
			char c = s.charAt(i);
			if (lower && LOWERCASE_CHARS.indexOf(c) >= 0) {
				lower = false;
			}
			if (numbers && NUMBERS.indexOf(c) >= 0) {
				numbers = false;
			}
			if (upper && UPPERCASE_CHARS.indexOf(c) >= 0) {
				upper = false;
			}
			if (specials && SPECIALS.indexOf(c) >= 0) {
				specials = false;
			}
		}
		return !(lower || numbers || upper || specials);
	}
}

string操作工具类

/**
 * String Utils
 * 尽量使用本类，不要引入多个包的StringUtils
 */
public class StringUtils {
	public static final String EMPTY = "";
	public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");

	/**
	 * 判断是否null或""
	 *
	 * @param str
	 * @return
	 */
	public static boolean isEmpty(String str) {
		return str == null ? true : str.length() == 0;
	}

	/**
	 * 去除空格后是否仍然为空
	 * @param s
	 * @return
	 */
	public static boolean isBlank(String s) {
		if (isEmpty(s)) {
			return true;
		}
		return s.trim().length() == 0;
	}

	/**
	 * 安全的toString，增加空的判断
	 * @param v
	 * @return
	 */
	public static String toString(Object v) {
		return toString(v, EMPTY);
	}

	/**
	 * 安全的toString，增加空的判断
	 * @param v
	 * @param nullStr
	 * @return
	 */
	public static String toString(Object v, String nullStr) {
		if (v == null) {
			return nullStr;
		} else {
			return v.toString();
		}
	}

	public static String toString(String[] array) {
		if (array == null || array.length == 0) {
			return "";
		}
		StringBuilder str = new StringBuilder();
		for (int i = 0; i < array.length; i++) {
			if (i > 0) {
				str.append(",");
			}
			str.append(array[i]);
		}
		return str.toString();
	}

	public static byte[] getBytes(String s) {
		return getBytes(s, DEFAULT_CHARSET);
	}

	public static byte[] getBytes(String s, Charset charset) {
		return s.getBytes(charset);
	}

	public static String getString(byte[] buffer) {
		return getString(buffer, DEFAULT_CHARSET);
	}

	public static String getString(byte[] buffer, Charset charset) {
		if (buffer == null) {
			return EMPTY;
		}
		return new String(buffer, charset);
	}

	/**
	 * 比较两个字符串是否相等
	 * @param lv
	 * @param rv
	 * @return
	 */
	public static boolean equals(String lv, String rv) {
		if (lv == null) {
			return rv == null;
		} else {
			if (rv == null) {
				return false;
			} else {
				return lv.equals(rv);
			}
		}
	}

	public static String repeat(String s, int n) {
		StringBuilder str = new StringBuilder();
		for (int i = 0; i < n; i++) {
			str.append(s);
		}
		return str.toString();
	}

	/**
	 * 打马赛克
	 *
	 * @param s
	 * @param leftChars
	 * @return
	 */
	public static String mosaicString(String s, int leftChars) {
		if (StringUtils.isEmpty(s)) {
			return s;
		}
		int n = s.length() - leftChars;
		if (n > 0) {
			return StringUtils.repeat("*", n) + s.substring(n);
		} else {
			return StringUtils.repeat("*", s.length());
		}
	}

	/**
	 * 打马赛克
	 *
	 * @param s
	 * @param leftChars
	 * @return
	 */
	public static String mosaicString(String s, int startChars, int leftChars) {
		if (StringUtils.isEmpty(s)) {
			return s;
		}

		if (s.length() >= startChars) {
			return s.substring(0, 2) + mosaicString(s.substring(2), leftChars);
		} else {
			return StringUtils.repeat("*", s.length());
		}
	}

	/**
	 * Get String suffix with length `n`
	 * @param s
	 * @param n
	 * @return
	 */
	public static String getSuffix(String s, int n) {
		if (isEmpty(s)) {
			return "";
		} else if (s.length() < n) {
			return s;
		} else {
			return s.substring(s.length() - n);
		}
	}

	/**
	 *
	 * @param buffer
	 * @param limitLength
	 * @return
	 */
	public static String bufferToString(byte[] buffer, int limitLength) {
		if (buffer == null) {
			return "";
		} else {
			return bufferToString(buffer, buffer.length, limitLength, DEFAULT_CHARSET);
		}
	}

	/**
	 *
	 * @param buffer
	 * @param actualLength
	 * @param limitLength
	 * @param charset
	 * @return
	 */
	public static String bufferToString(byte[] buffer, int actualLength, int limitLength, Charset charset) {
		if (actualLength > limitLength) {
			ByteBuffer byteBuffer = ByteBuffer.wrap(buffer, 0, limitLength);
			return new StringBuilder(charset.decode(byteBuffer))
				.append("n... (total ").append(actualLength).append(" bytes)")
				.toString();
		} else {
			ByteBuffer byteBuffer = ByteBuffer.wrap(buffer, 0, actualLength);
			return charset.decode(byteBuffer).toString();
		}
	}

	/**
	 * split and trim and normalized
	 * @param text
	 * @return
	 */
	public static List<String> splitAndTrim(String text, String regex) {
		List<String> result = new ArrayList<String>();
		if (isEmpty(text)) {
			return result;
		}
		for (String s: text.split(regex)) {
			if (StringUtils.isEmpty(s)) {
				continue;
			}
			s = s.trim();
			if (StringUtils.isEmpty(s)) {
				continue;
			}
			result.add(s);
		}
		return result;
	}
	
}

最后

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