本篇文章将为您介绍在 Java 开发中较常见的几种工具类，附带具体代码实例，希望可以帮助到你的学习。

一、FileUtils

private static void fileUtilsTest() {
    try {
        //读取文件内容
        String readFileToString = FileUtils.readFileToString(new File("D:\guor\data\test20211022000000.txt"));
        System.out.println(readFileToString);
        //删除文件夹
        FileUtils.deleteDirectory(new File("D:\guor1\data1"));
        FileUtils.deleteQuietly(new File("D:\guor\data"));
        //清空文件夹
        FileUtils.cleanDirectory(new File("D:\guor\data"));
        //判断文件内容是否一致
        boolean contentEquals = FileUtils.contentEquals(new File("D:\guor\data\test20211022000000.txt"), new File("D:\guor\data\testNew20211021000000.txt"));
        boolean contentEquals2 = FileUtils.contentEquals(new File("D:\guor\data\中文20211021100000.txt"), new File("D:\guor\data\中文New20211022100000.txt"));
        System.out.println(contentEquals+","+contentEquals2);
        //拷贝特定类型的文件
        FileUtils.copyDirectory(new File("D:\guor\data"), new File("D:\guor\data2"), new FileFilter() {
            @Override
            public boolean accept(File pathname) {
                if(pathname.getName().startsWith("test")) {
                    return true;
                }
                return false;
            }
        });
        FileUtils.moveDirectory(new File("D:\guor\data"), new File("D:\guor\data3"));
        FileUtils.moveFileToDirectory(new File("D:\guor\data"), new File("D:\guor\data3"), true);
        FileUtils.moveToDirectory(new File("D:\guor\data"), new File("D:\guor\data4"), true);
        boolean directoryContains = FileUtils.directoryContains(new File("D:\guor\data"), new File("D:\guor\data\test20211022000000.txt"));
        System.out.println(directoryContains);
        directoryContains = FileUtils.directoryContains(new File("D:\guor\data"), new File("*.txt"));
        System.out.println(directoryContains);
        //获取某文件夹下特定格式文件
        File[] listFiles = new File("D:\guor\data").listFiles(new FilenameFilter() {
            @Override
            public boolean accept(File dir, String name) {
                return name.startsWith("test");
            }
        });
 
        System.out.println(Arrays.toString(listFiles));
        //获取系统temp文件夹路径
        File tempDirectory = FileUtils.getTempDirectory();
        System.out.println(tempDirectory);
        //获取系统用户文件夹路径
        File userDirectory = FileUtils.getUserDirectory();
        System.out.println(userDirectory);
 
        //查看是否是新建的文件夹
        SimpleDateFormat sdf =new SimpleDateFormat("yyyyMMddHHmmss" );
        Date parse = sdf.parse("20210206134900");
        boolean fileNewer = FileUtils.isFileNewer(new File("D:\guor\data"), parse);
        System.out.println(fileNewer);
        //更新文件修改时间，如果不存在，则新建；
        FileUtils.touch(new File("D:\guor\data\test20211022000000.txt"));
        //延迟查看文件是否存在
        boolean waitFor = FileUtils.waitFor(new File("D:\guor\data\testNew20211021000000.txt"), 5);
        System.out.println(waitFor);
    } catch (Exception e) {
        System.out.println(e);
    }
}

//根据文件修改时间排序
public static void test02() {
    String dir = "D:\data";
    File[] listFiles = new File(dir).listFiles();
    List<File> asList = Arrays.asList(listFiles);
    for(File file:listFiles) {
        System.out.println(file);
    }
    Collections.sort(asList, new Comparator<File>() {
        @Override
        public int compare(File o1, File o2) {
            if(o1.lastModified()<o2.lastModified()) {
                return -1;
            }else if(o1.lastModified()>o2.lastModified()) {
                return 1;
            }else {
                return 0;
            }
        }
    });
    System.out.println("sort...");
    for(File file:listFiles) {
        System.out.println(file+","+file.lastModified());
    }
}

二、StringUtil

private static void stringUtilsTest() {
    String str = "hello world";
    //将第一个字符大写
    String capitalize = StringUtils.capitalize(str);
    System.out.println(capitalize);//Hello
    //两边空格补齐
    String center = StringUtils.center(str, 7);
    System.out.println(center);// hello
    String center = StringUtils.center(str, 7, "*");
    System.out.println(center);//*hello*
    //chomp剔除字符串最后一个是
或
或

    String chomp = StringUtils.chomp(str);
    System.out.println(chomp);
    //chop剔除字符串最后一个字符（如果最后一个是
或
或
也剔除掉）
    String chop = StringUtils.chop(str);
    System.out.println(chop);//hello worl
    //是否包含任意字符
    boolean containsAny = StringUtils.containsAny(str, "W");
    System.out.println(containsAny);
    //是否包含任意字符，忽略大小写
    containsAny = StringUtils.containsIgnoreCase(str, "W");
    System.out.println(containsAny);
 
    //有意思
    int indexOfAnyBut = StringUtils.indexOfAnyBut(str, "hello orld");
    System.out.println(indexOfAnyBut);
 
    //两个字符串从第几位开始不同
    int indexOfDifference = StringUtils.indexOfDifference(str, str);
    System.out.println(indexOfDifference);
    indexOfDifference = StringUtils.indexOfDifference(str, str+"zs");
    System.out.println(indexOfDifference);
    indexOfDifference = StringUtils.indexOfDifference(str, "he llo");
    System.out.println(indexOfDifference);
 
    //判断是否是正整数
    boolean isNumeric = StringUtils.isNumeric(str);
    System.out.println(isNumeric);//false
    isNumeric = StringUtils.isNumeric("1234dd");
    System.out.println("1234dd:"+isNumeric);//false
    isNumeric = StringUtils.isNumeric("1234 ");
    System.out.println("1234 :"+isNumeric);//false
    isNumeric = StringUtils.isNumeric("1.234");
    System.out.println("1.234:"+isNumeric);//false
    isNumeric = StringUtils.isNumeric("1234");
    System.out.println("1234:" + isNumeric);//true
    isNumeric = StringUtils.isNumeric("-1234");
    System.out.println("-1234:" + isNumeric);//false
    //判断是否是正整数或空格
    boolean isNumeric = StringUtils.isNumericSpace(str);
 
    //将数组变为字符串，并添加字符进行分割
    Object[] array = new Object[] {"zs",18,"男",666,777};
    String join = StringUtils.join(array);
    System.out.println(Arrays.toString(array));
    join = StringUtils.join(array, "*");
    System.out.println(join);
    Object[] array = new Object[] {"zs",18,"男",666,777};
    String join = StringUtils.join(array, ";", 2, 5);
    System.out.println(join);
 
    String remove = StringUtils.remove(str, "hello");
    System.out.println(remove);// world
    String repeat = StringUtils.repeat(str, 3);
    System.out.println(repeat);//hello worldhello worldhello world
    repeat = StringUtils.repeat(str, ",", 3);
    System.out.println(repeat);//hello world,hello world,hello world
 
    //分别替换
    String[] list =  new String[] {"hello", "girl"};
    String[] replacementList =  new String[] {"say", "woman"};
    String str2 = "hello world,hello boy,hello girl.";
    String replaceEach = StringUtils.replaceEach(str2, list, replacementList);
    System.out.println(replaceEach);//say world,say boy,say woman.
 
    //只替换第一个匹配的字符串
    String replaceOnce = StringUtils.replaceOnce("hello world,hello boy,hello girl.", "hello", "say");
    System.out.println(replaceOnce);//say world,hello boy,hello girl.
 
    //截取某字符后面的部分
    String substringAfterLast = StringUtils.substringAfterLast("hello world,hello boy,hello girl.", " ");
    System.out.println(substringAfterLast);//girl.
 
    String substringBeforeLast = StringUtils.substringBeforeLast("hello world,hello boy,hello girl.", " ");
    System.out.println(substringBeforeLast);//hello world,hello boy,hello
}

三、CollectionUtils

private static void collectionUtilsTest() {
    List<String> list = new ArrayList<String>();
    list.add("zhangsan");
    list.add("dalian");
    list.add("gateway");
    list.add("gateway");
    list.add("28");
    list.add("35");
    //查找第一个符合条件的元素
    Object find = CollectionUtils.find(list, new Predicate() {
        @Override
        public boolean evaluate(Object arg0) {
            if(StringUtils.isNumeric(arg0.toString())) {
                return false;
            }
            return true;
        }
    });
 
    //排除不符合条件的元素
    Collection select = CollectionUtils.select(list, new Predicate() {
        @Override
        public boolean evaluate(Object arg0) {
            if(StringUtils.isNumeric(arg0.toString())) {
                return false;
            }
            return true;
        }
    });
    System.out.println(list);//[zhangsan, dalian, 28]
    System.out.println(find);//zhangsan
    System.out.println(select);//[zhangsan, dalian]
 
 
    List<String> list2 = new ArrayList<String>();
    list2.add("zhangsan");
    list2.add("dalian2");
    list2.add("282");
    //查看两个集合中是否有相同的元素
    boolean containsAny = CollectionUtils.containsAny(list, list2);
    System.out.println(containsAny);//true
 
    //查找集合中某元素的个数
    int countMatches = CollectionUtils.countMatches(list, new Predicate() {
        @Override
        public boolean evaluate(Object arg0) {
            if(StringUtils.isNumeric(arg0.toString())) {
                return true;
            }
            return false;
        }
    });
    System.out.println(countMatches);
 
    //查找集合中是否存在某元素
    boolean exists = CollectionUtils.exists(list, new Predicate() {
        @Override
        public boolean evaluate(Object arg0) {
            if(StringUtils.isNumeric(arg0.toString())) {
                return true;
            }
            return false;
        }
    });
 
    System.out.println(exists);
 
    //删除集合中的某些元素
    System.out.println(list);//[zhangsan, dalian, 打法, 28, 35]
    CollectionUtils.filter(list, new Predicate() {
        @Override
        public boolean evaluate(Object arg0) {
            if(StringUtils.isNumeric(arg0.toString())) {
                return false;
            }
            return true;
        }
    });
 
    System.out.println(list);//[zhangsan, dalian, 打法]
 
    //查找集合中符合条件的第一个元素
    Object find = CollectionUtils.find(list, new Predicate() {
        @Override
        public boolean evaluate(Object arg0) {
            if(StringUtils.isNumeric(arg0.toString())) {
                return false;
            }
            return true;
        }
    });
    System.out.println(find);//zhangsan
 
    //闭包回调函数
    System.out.println(list);
    CollectionUtils.forAllDo(list, new Closure() {
        @Override
        public void execute(Object arg0) {
            if(StringUtils.isNumeric(arg0.toString())) {
                work(arg0);
            }
        }
    });
    System.out.println(list);
 
    //查找集合中元素的个数
    System.out.println(list);//[zhangsan, dalian, gateway, gateway, 28, 35]
    Map cardinalityMap = CollectionUtils.getCardinalityMap(list);
    System.out.println(cardinalityMap);//{35=1, 28=1, zhangsan=1, dalian=1, gateway=2}
 
    //查找两个集合中的相同元素
    List<String> list2 = new ArrayList<String>();
    list2.add("lisi");
    list2.add("beijing");
    list2.add("gateway");
    list.add("19");
    Collection intersection = CollectionUtils.intersection(list, list2);
    System.out.println(intersection);
 
    //获取两个List<Map<String, Object>>中相同的部分，可以用于对比两个库中的相同表数据是否相等
    List<Map<String, Object>> list3 = new ArrayList<Map<String,Object>>();
    List<Map<String, Object>> list4 = new ArrayList<Map<String,Object>>();
    Map<String, Object> map1 = new HashMap<String, Object>();
    map1.put("name", "zhangsan");
    map1.put("age", 18);
    map1.put("address", "dalian");
    Map<String, Object> map2 = new HashMap<String, Object>();
    map2.put("name", "张三");
    map2.put("age", "十八");
    map2.put("address", "大连");
    list3.add(map1);
    list3.add(map2);
 
    Map<String, Object> map3 = new HashMap<String, Object>();
    map3.put("name", "李四");
    map3.put("age", "十八");
    map3.put("address", "大连");
    list4.add(map2);
    list4.add(map1);
    list3.add(map3);
    System.out.println(list3);
    System.out.println(list4);
    Collection intersection = CollectionUtils.intersection(list3, list4);
    System.out.println(intersection);//[{address=dalian, name=zhangsan, age=18}]
 
    //判断两个集合是否相同
    boolean equalCollection = CollectionUtils.isEqualCollection(list3, list4);
    System.out.println(equalCollection);
 
    判断param2是否包含param1，且不能完全相同
    System.out.println(list3);//[{address=dalian, name=zhangsan, age=18}, {address=大连, name=张三, age=十八}, {address=大连, name=李四, age=十八}]
    System.out.println(list4);//[{address=大连, name=张三, age=十八}, {address=dalian, name=zhangsan, age=18}]
    boolean properSubCollection = CollectionUtils.isProperSubCollection(list4, list3);
    System.out.println(properSubCollection);//true
 
    //断定某集合是否含有某元素，如果包含则抛异常（我觉得应该少用为妙）
    System.out.println(list);//[zhangsan, dalian, gateway, gateway, 28, 35]
    Collection predicatedCollection = CollectionUtils.predicatedCollection(list, new Predicate() {
        @Override
        public boolean evaluate(Object object) {
            if(StringUtils.isNumeric(object.toString())) {
                return false;
            }
            return true;
        }
    });
    System.out.println(predicatedCollection);//Exception in thread "main" java.lang.IllegalArgumentException: Cannot add Object '28' - Predicate rejected it
    List<String> list2 = new ArrayList<String>();
    list2.add("gateway");
    System.out.println(list);
    System.out.println(list2);
    //删除list1中的list2
    Collection removeAll = CollectionUtils.removeAll(list, list2);
    System.out.println(removeAll);
 
    //反转数组
    String[] array = new String[] {"zs","ls","ww"};
    System.out.println(StringUtils.join(array, ","));//zs,ls,ww
    CollectionUtils.reverseArray(array);
    System.out.println(StringUtils.join(array, ","));//ww,ls,zs
 
    删除list1中的list2
    List<String> list2 = new ArrayList<String>();
    list2.add("zhangsan");
    list2.add("dalian");
    Collection subtract = CollectionUtils.subtract(list, list2);
    System.out.println(subtract);
 
    //更改集合中的特定值
    Collection collect = CollectionUtils.collect(list, new Transformer() {
        @Override
        public Object transform(Object arg0) {
            if(StringUtils.isNumeric(arg0.toString())) {
                return 15;
            }
            return arg0;
        }
    });
    System.out.println(list);//[zhangsan, dalian, 28, 35]
    System.out.println(collect);//[zhangsan, dalian, 15, 15]
 
    //更改集合中的特定值，改变集合本身
    System.out.println(list);//[zhangsan, dalian, gateway, gateway, 28, 35]
    CollectionUtils.transform(list, new Transformer() {
 
        @Override
        public Object transform(Object input) {
            if(StringUtils.isNumeric(input.toString())) {
                return 15;
            }
            return input;
        }
    });
    System.out.println(list);//[zhangsan, dalian, gateway, gateway, 15, 15]
    List<String> list2 = new ArrayList<String>();
    list2.add("docker");
    list2.add("zhangsan");
    System.out.println(list);
    System.out.println(list2);
    //将list和list2中的元素合并，但去除list2中的重复元素
    Collection union = CollectionUtils.union(list, list2);
    System.out.println(union);
}

private static void work(Object obj){
    System.out.println("闭包回调函数:我是数字，"+obj);
}

四、ArrayUtils

private static void arrayUtilsTest() {
    String[] array =new String[] {"zs", "ls"};
 
    //增加元素
    Object[] add = ArrayUtils.add(array, "ww");
    System.out.println(StringUtils.join(add, ","));//zs,ls,ww
 
    //合并数组
    String[] array2 =new String[] {"ww", "ss"};
    Object[] addAll = ArrayUtils.addAll(array1, array2);
    System.out.println(StringUtils.join(addAll, ","));//zs,ls,ww,ss
 
    //克隆数组
    Object[] clone = ArrayUtils.clone(array);
    System.out.println(StringUtils.join(clone, ","));//zs,ls
 
 
    boolean contains = ArrayUtils.contains(array, "ww");
    boolean contains1 = ArrayUtils.contains(array, "zs");
    System.out.println(contains+","+contains1);//false,true
}

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