学习笔记_CommonLang_StringUtils
public static boolean isEmpty(String str) { return str == null || str.length() == 0; } public static String trim(String str) { return str == null ? null : str.trim(); } public static String trimToEmpty(String str) { return str == null ? EMPTY : str.trim(); } /** * <p>Compares two Strings, returning true if they are equal.</p> * * StringUtils.equals(null, null) = true * StringUtils.equals(null, "abc") = false * StringUtils.equals("abc", null) = false * StringUtils.equals("abc", "abc") = true * StringUtils.equals("abc", "ABC") = false */ public static boolean equals(String str1, String str2) { return str1 == null ? str2 == null : str1.equals(str2); } public static boolean equalsIgnoreCase(String str1, String str2) { return str1 == null ? str2 == null : str1.equalsIgnoreCase(str2); } /** * <p>Checks if String contains a search String, handling null.</p> * * StringUtils.contains(null, *) = false * StringUtils.contains(*, null) = false * StringUtils.contains("", "") = true * StringUtils.contains("abc", "") = true * StringUtils.contains("abc", "a") = true * StringUtils.contains("abc", "z") = false */ public static boolean contains(String str, String searchStr) { if (str == null || searchStr == null) { return false; } return str.indexOf(searchStr) >= 0; } public static String left(String str, int len) { if (str == null) { return null; } if (len < 0) { return EMPTY; } if (str.length() <= len) { return str; } return str.substring(0, len); } public static int length(String str) { return str == null ? 0 : str.length(); } public static boolean isNumeric(String str) { if (str == null) { return false; } int sz = str.length(); for (int i = 0; i < sz; i++) { if (Character.isDigit(str.charAt(i)) == false) { return false; } } return true;} public static String defaultString(String str) { return str == null ? EMPTY : str; } /** * <pre> * StringUtils.join(null, *) = null * StringUtils.join([], *) = "" * StringUtils.join([null], *) = "" * StringUtils.join(["a", "b", "c"], "--") = "a--b--c" * StringUtils.join(["a", "b", "c"], null) = "abc" * StringUtils.join(["a", "b", "c"], "") = "abc" * StringUtils.join([null, "", "a"], ',') = ",,a" * </pre> * * <pre> * StringUtils.repeat(null, 2) = null * StringUtils.repeat("", 0) = "" * StringUtils.repeat("", 2) = "" * StringUtils.repeat("a", 3) = "aaa" * StringUtils.repeat("ab", 2) = "abab" * StringUtils.repeat("a", -2) = "" * </pre> * * * <pre> * StringUtils.abbreviate(null, *) = null * StringUtils.abbreviate("", 4) = "" * StringUtils.abbreviate("abcdefg", 6) = "abc..." * StringUtils.abbreviate("abcdefg", 7) = "abcdefg" * StringUtils.abbreviate("abcdefg", 8) = "abcdefg" * StringUtils.abbreviate("abcdefg", 4) = "a..." * StringUtils.abbreviate("abcdefg", 3) = IllegalArgumentException * </pre> */