1.文件管理
(1)获取不带扩展名的文件名
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| public static String getFileNameWithoutExtension(File file) {
String name = file.getName();
int lastIndexOf = name.lastIndexOf('.');
return lastIndexOf == -1 ? name : name.substring(0, lastIndexOf);
}
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(2)删除目录及目录下的所有文件
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public void delDir(Path directory) {
try {
Files.walk(directory).sorted(Comparator.reverseOrder()).map(Path::toFile).forEach(File::delete);
} catch (Exception e) {
e.printStackTrace();
}
}
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(3)解压缩文件
将sourceZipFilePath.zip文件解压缩到targetDir目里。
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public void unZipFile(String sourceZipFilePath, String targetDirPath) {
new File(targetDirPath).mkdirs();
try (ZipFile zip = new ZipFile(sourceZipFilePath,Charset.forName("GBK"))) {
Enumeration enums = zip.entries();
while (enums.hasMoreElements()) {
ZipEntry entry = (ZipEntry) enums.nextElement();
try(
BufferedInputStream bufferis = new BufferedInputStream(zip.getInputStream(entry));
BufferedOutputStream bufferos = new BufferedOutputStream(
new FileOutputStream(sourceDir + "\\" + entry.getName()));
){
byte[] b = new byte[1024];
int len = 0;
while ((len = bufferis.read(b)) != -1) {
bufferos.write(b, 0, len);
}
}
}
} catch (IOException e) {
LOGGER.log(Level.ERROR, "文件解压失败。");
e.printStackTrace();
}
}
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(4)压缩文件
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| public void zipFile(List<String> sourceFile, String targetFile) {
try (ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(targetFile), Charset.forName("GBK"))) {
for (String f1 : sourceFile) {
if (new File(f1).exists()) {
try (FileInputStream f = new FileInputStream(f1)) {
ZipEntry zipEntry = new ZipEntry(new File(f1).getName());
zos.putNextEntry(zipEntry);
byte[] buffer = new byte[1024];
int len;
while ((len = f.read(buffer)) > 0) {
zos.write(buffer, 0, len);
}
}
}
}
} catch (Exception e) {
LOGGER.log(Level.ERROR, targetFile + "文件压缩失败。");
e.printStackTrace();
}
LOGGER.log(Level.INFO, targetFile + "文件压缩完成。");
}
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2.日期
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Date now = new Date();
System.out.println("当前时间: " + now);
Calendar calendar = Calendar.getInstance();
System.out.println("当前时间: " + calendar.getTime());
Date date = new Date();
calendar.setTime(date);
calendar.add(Calendar.DAY_OF_YEAR, -6);
Date sixDaysAgo = calendar.getTime();
System.out.println("六天前的日期是: " + sixDaysAgo);
LocalDateTime now1 = LocalDateTime.now();
System.out.println("当前时间: " + now1);
System.out.println("当前时间增加1分钟: " + now1.plusMinutes(1));
System.out.println("当前时间比较: " + ChronoUnit.MILLIS.between(now1,LocalDateTime.now()));;
Instant now2 = Instant.now();
System.out.println("当前时间now2: " + now2);
ZonedDateTime zonedNow = now2.atZone(ZoneId.systemDefault());
System.out.println("当前时间（系统时区）now2: " + zonedNow);
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3.XML文件读写
(1)读取带有命名空间的XML文件，并输出字符串
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| public void exportXmlContent(String id,String uml) {
InputSource inputSource = new InputSource(uml);
try {
String xmiNamespacePrefix = "xmi";
String xmiNamespaceUri = "http://www.omg.org/XMI";
xpath.setNamespaceContext(new NamespaceContextImpl(xmiNamespaceUri, xmiNamespacePrefix));
XPath xpath = XPathFactory.newInstance().newXPath();
String xpathExpress = "//packagedElement[@xmi:id=\"" + id + "\"]";
Node node = (Node) xpath.evaluate(xpathExpress, inputSource, XPathConstants.NODE);
System.out.println(node.getNodeName() + "#"+node.getAttributes().getNamedItem("xmi:id") ;
StringWriter sw = new StringWriter();
Transformer t = TransformerFactory.newInstance().newTransformer();
t.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
t.transform(new DOMSource(node), new StreamResult(sw));
System.out.println(sw.toString());
} catch (Exception e) {
e.printStackTrace();
}
}
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(2)Xml文件调用
Node 类型可以直接转换成Element类型，用于处理元素的属性设置。
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| XPathFactory xpathFactory = XPathFactory.newInstance();
xpath = xpathFactory.newXPath();
URL xmlpath = AXMLFactory.class.getClassLoader().getResource("Browser.xml");
inputSource = new InputSource(xmlpath.toString());
String xpathExpress ="//Elements/Element[@name='Package']";
NodeList nodeList = xpath.evaluate(xpathExpress, inputSource,XPathConstants.NODESET);
for(int i=0;i<nodeList.getLength();i++) {
Node node=nodeList.item(i);
Element el=(Element)node;
System.out.println(node.getNodeName()+";"+node.getNodeValue()+";"+el.getAttribute("name"));
}
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4.stream
(1)filter 过滤(查找)元素
函数语法：
Stream<TreeElement> java.util.stream.Stream.filter(Predicate<? super TreeElement> predicate)
(a)filter(判断是否需要的元素).collect(保存为新的List输出).
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List<TreeElement> tlist1=tlist.stream().filter(x->"name".equals(x.getName()))
.collect(Collectors.toList());
User match = users.stream().filter((user) -> user.getId() == 1).findAny().get();
List<String> list = Arrays.asList("aa", "bb", "", "cc");
List<String> filtered = list.stream().filter(string -> !string.isEmpty()).collect(Collectors.toList());
String str = filtered.stream().collect(Collectors.joining(","));
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(b)字符串数组(fileNames)中获取指定的元素(.msnotation)。如果为null，返回空字符串；不为null，返回指定字符。
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| String[] fileNames=new File(targetDir).list();
String ret=Stream.of(fileNames).filter(x->x.contains(".msnotation")).findFirst().orElseGet(()->"");
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(2)map 遍历元素转换成新元素
map()方法是流（Stream）类中的一个中间操作方法，它接受一个函数作为参数，并将该函数应用于流中的每个元素，然后返回一个新的流，其中包含由该函数的结果组成的元素。
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| List<Integer> list = Arrays.asList(1, 3, 4, 99, 20);
List<Integer> squaresList = list .stream().map( i -> i*i).distinct().collect(Collectors.toList());
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(3)collect 保存数据集
(一般与map、filter联用，放在最后作为新数据保存。)
函数语法：
List<TreeElement> java.util.stream.Stream.collect(Collector<? super TreeElement, Object, List<TreeElement>> collector)
把数据流保存到新的数组或集合中。
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| Map<String, Stream> map = new HashMap<String, Stream>();
map.put("001", new Stream("张三","西安"));
map.put("002", new Stream("李四","铜川"));
List<Map<String, Stream>> list = new ArrayList()
list.add(map);
List<Stream> streams = list.stream().map(item -> item.get("001")).collect(Collectors.toList());
Map<String, Stream> aqglEmpVoMap = streams .stream().collect(Collectors.toMap(Stream::getEmpId, Stream-> Stream));
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(4)summaryStatistics 输出最大、最小、平均值
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| List<Integer> list = Arrays.asList(1, 3, 4, 99, 20);
IntSummaryStatistics statistics = list.stream().mapToInt(x -> x).summaryStatistics();
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(5)集合中交集、差集、并集
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List<String> list1 = Arrays.asList("阿卫", "阿辉", "阿杰", "阿成");
List<String> list2 = Arrays.asList("阿悦", "阿楠", "阿洁", "阿锋");
List<String> collect = list1.stream().filter(list2::contains).collect(Collectors.toList());
List<String> list3 = list1.stream().filter(item -> !list2.contains(item)).collect(toList());
list3 = list2.stream().filter(item -> !list1.contains(item)).collect(toList());
List<String> listAll = list1.parallelStream().collect(Collectors.toList());
List<String> listAll2 = list2.parallelStream().collect(Collectors.toList());
listAll.addAll(listAll2);
List<String> listAllDistinct = listAll.stream().distinct().collect(Collectors.toList());
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(6)Map转List
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| Map<String,String> map = new HashMap<>(3);
map.put("600519","贵州茅台");
map.put("601398","工商银行");
map.put("300750","宁德时代");
List<Object> list1 = map.entrySet().stream().map(ent ->ent.getKey()+":"+ent.getValue()).collect(Collectors.toList());
List<Object> list2 = map.entrySet().stream().map(ent -> ent.getKey()).collect(Collectors.toList());
List<Object> list3 = map.entrySet().stream().map(ent -> ent.getValue()).collect(Collectors.toList());
list1.forEach(listFor -> System.out.println(listFor));
System.out.println("map数据格式:" + map);
System.out.println("list数据格式:" + list1);
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(7)List转Map
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| Stream streamTest = new Stream("张三","西安","13345");
List<Stream> list1 = new ArrayList<>();
list1.add(streamTest);
Map result = list1.stream().collect(Collectors.toMap(p -> p.getIdcard(), p -> p.getName(), (k1, k2) -> k1));
Map<String, String> result1 = list1.stream().collect(Collectors.toMap(Stream::getIdcard, Stream::getName));
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5.反射调用
示例静态类
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| class MyClass {
public static String DATA="静态字段数据";
public static String myStaticMethod(int number, String text) {
return "Number: " + number + ", Text: " + text;
}
}
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(1)调用带参数有返回值的静态方法
转换对象类型(用instanceof判断)：MyClass mc=MyClass.cast(Class对象);
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| import java.lang.reflect.Method;
public class ReflectionExample {
public static void main(String[] args) {
try {
Class<?> clazz = Class.forName("com.example.MyClass");
Method method = clazz.getMethod("myStaticMethod", int.class, String.class);
Object result = method.invoke(null, 42, "Hello");
System.out.println("Return value: " + result);
} catch (Exception e) {
e.printStackTrace();
}
}
}
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(2)静态字段
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| Field field = clazz.getDeclaredField("LOADED_RESOURCESET");
import java.lang.reflect.Method;
public class ReflectionExample {
public static void main(String[] args) {
try {
Class<?> clazz = Class.forName("com.example.MyClass");
Field field = clazz.getDeclaredField("DATA");
String str=(String)field.get(null);
System.out.println("Return value: " + str);
} catch (Exception e) {
e.printStackTrace();
}
}
}
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6.Comparator排序
(1)先按sort字段排序，再中文名称排序。
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Collator collator = Collator.getInstance(java.util.Locale.CHINA);
teList.sort(Comparator.<TreeElement>comparingDouble((obj -> Double.parseDouble(obj.getSort()))).
thenComparing((a,b)->collator.compare(a.getName(), b.getName())));
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(2)先分组排序，再每个组内按中文排序
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Collator collator = Collator.getInstance(java.util.Locale.CHINA);
Map<String, List<TreeElement>> map = treeList.stream()
.collect(Collectors.groupingBy(TreeElement::getModelTypeCnName));
map.forEach((key,value)->value.sort((a,b)->collator.compare(a.getName(), b.getName())));
map=map.entrySet().stream().sorted(Map.Entry.comparingByKey(collator)).collect(Collectors.toMap(Map.Entry::getKey,Map.Entry::getValue, (oldVal, newVal) -> oldVal, LinkedHashMap::new));
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7. java规范
1.包声明
2.导入声明
3.类或接口声明
4.常量声量
5.字段声明(按照普通字段、静态字段；再按照private、protected、public)
6.构造方法或初始块
7.方法声明(按照普通方法、静态方法)
8.内部类声明
示例：
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| package com.example.myapp;
import java.util.List;
import java.util.Map;
import java.io.IOException;
public class MyClass {
public static final int MAX_SIZE = 100;
private int id;
public static MyClass instance;
public MyClass() {
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8.获取系统信息
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System.out.println("当前java版本为：" + System.getProperty("java.version"));
System.out.println("Java 运行时环境的安装目录：" + System.getProperty("java.home"));
System.out.println("当前操作系统为：" + System.getProperty("os.name"));
System.out.println("当前用户为：" + System.getProperty("user.name"));
System.out.println("当前用户目录为：" + System.getProperty("user.home"));
System.out.println("当前工作目录为：" + System.getProperty("user.dir"));
URL resourceURL = CustomClass.class.getClassLoader().getResource("");
System.out.println("Resource URL: " + resourceURL);
String classpath = Input.class.getProtectionDomain().getCodeSource().getLocation().getPath();
System.out.println("Class Path from JAR: " + classpath);
System.out.println("当前类路径的根目录："+Input.class.getResource("/").getPath());
System.out.println("当前类路径："+Input.class.getResource("").getPath());
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9.Map
(1)删除元素
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map.keySet().removeIf(key -> map.get(key) == null);
Map<String, String> filteredMap = map.entrySet().stream().filter(entry -> entry.getValue() != null).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
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10.Optional
1.ifPresent()
ifPresent 相当于判断 !=null , 不为空才执行里面的代码:
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| Student student1 = new Student("王五", 80);
Optional<Student> optional = Optional.ofNullable(student1);
optional.ifPresent(name -> System.out.println("student1不为空，姓名为："+name.getName()));
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2.ifPresentOrElse()
java 9里新增了 ifPresentOrElse()，当 Optional 里的值不为空则执行第一个参数里的代码，为空则执行第二个参数的代码，相当于 if-else :
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| Student student = new Student("王五", 80);
Optional<Student> optional = Optional.ofNullable(student);
optional.ifPresentOrElse( value -> System.out.println("student不为空，姓名："+value.getName()), () -> System.out.println("student为空") );
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