1、ByteArrayInputStream、ByteArrayOutputStream
String str ="ZHANGSAN";
//System.out.println(str.toLowerCase());
ByteArrayInputStream inputStream = newByteArrayInputStream(str.getBytes());
ByteArrayOutputStream outputStream = newByteArrayOutputStream();
intb;
while((b = inputStream.read()) != -1){
charlowerCase = Character.toLowerCase((char)b);
outputStream.write(lowerCase);
}
byte[] lowerCases = outputStream.toByteArray();
System.out.println(newString(lowerCases,0, lowerCases.length));
全部在内存中完成byte的转换
2、PrintStream：向目标打印
属于OutputStream的实现类，向目标(可能是文件、标准输出屏幕、输出流、网络等)打印各种样式，不过比一般的输出提供了更多的打印方式，可以打印各种数据类型和样式等
OutputStream outputStream = System.out;
outputStream.write("helloABC张三".getBytes());
outputStream.close();
列出当前操作系统的系统参数，输出到文件中
PrintStream printStream =newPrintStream("hello.txt");
System.getProperties().list(printStream);
printStream.close();
3、InputStreamReader、OutputStreamWriter， 计算机存储都是字节流的形式，而读取到内存中需要识别一个个的字符(人只能识别字符)，有可能1个字节就代表一个字符(例如英文),也有可能多个字节才能转换成一个字符(例如中文)，如果中间存在丢失或无法转换，则看到的就是一堆?
InputStreamReader:将输入的内容字节变成字符
OutputStreamWriter:将输出的内容从字符变成字节
4、合并流：SequenceInputStream
File file1 =newFile("hello.txt");
File file2 = newFile("test.txt");
InputStream inputStream1 = newFileInputStream(file1);
InputStream inputStream2 = newFileInputStream(file2);
SequenceInputStream sequenceInputStream = newSequenceInputStream(inputStream1,
inputStream2);
BufferedInputStream bufferedInputStream = newBufferedInputStream(sequenceInputStream);
intc;
while((c = bufferedInputStream.read()) != -1){
System.out.print((char)c);
}
bufferedInputStream.close();
sequenceInputStream.close();
inputStream1.close();
inputStream2.close();
测试结果:helloworld
在实验中，从bufferedInputStream去取到两个文件大小相加的byte数组中,代码如下，转换出来有问题，有点奇怪，只读到了前一个流中的内容，后面一个流中的内容没读取进来。思考中...
File file1 =newFile("hello.txt");
File file2 = newFile("test.txt");
InputStream inputStream1 = newFileInputStream(file1);
InputStream inputStream2 = newFileInputStream(file2);
SequenceInputStream sequenceInputStream = newSequenceInputStream(inputStream1,
inputStream2);
BufferedInputStream bufferedInputStream = newBufferedInputStream(sequenceInputStream);
intlength = (int) (file1.length() + file2.length());
byte[] b =newbyte[length];
bufferedInputStream.read(b, 0, length);
System.out.println(newString(b,0,length));
bufferedInputStream.close();
sequenceInputStream.close();
inputStream1.close();
inputStream2.close();
测试结果如下：hello
5、Zip压缩与解压
压缩程序：
ZipOutputStream zipOutputStream =newZipOutputStream(newFileOutputStream("hello.zip"));
zipOutputStream.setLevel(9);
ZipEntry zipEntry = newZipEntry("a.txt");
zipOutputStream.putNextEntry(zipEntry);
BufferedInputStream bufferedInputStream = newBufferedInputStream(newFileInputStream("test.txt"));
intcontent;
while((content = bufferedInputStream.read()) != -1){
zipOutputStream.write(content);
}
bufferedInputStream.close();
zipOutputStream.closeEntry();
zipOutputStream.flush();
zipOutputStream.close();
解压程序：
ZipInputStream zipInputStream =newZipInputStream(newFileInputStream("hello.zip"));
ZipEntry zipEntry = null;
while((zipEntry = zipInputStream.getNextEntry()) !=null) {
BufferedOutputStream bufferedOutputStream = newBufferedOutputStream(
newFileOutputStream(zipEntry.getName()));
intcontent =0;
while((content = zipInputStream.read()) != -1){
bufferedOutputStream.write(content);
}
bufferedOutputStream.flush();
bufferedOutputStream.close();
}
zipInputStream.close();
6、zip压缩某目录下的所有文件及子文件
publicvoidzipDirectory(File pathname, ZipOutputStream zipOutputStream)throwsException {
if(!pathname.isDirectory()) {
return;
}
File[] files = pathname.listFiles();
for(File file : files) {
if(file.isDirectory()) {
zipDirectory(file, zipOutputStream);
} else{
ZipEntry zipEntry = newZipEntry(pathname.getName() + File.separator
+ file.getName());
zipOutputStream.putNextEntry(zipEntry);
BufferedInputStream bufferedInputStream = newBufferedInputStream(
newFileInputStream(file));
inti;
while((i = bufferedInputStream.read()) != -1) {
zipOutputStream.write(i);
}
bufferedInputStream.close();
zipOutputStream.flush();
zipOutputStream.closeEntry();
}
}
}
问题：中文编码存在问题，建议选用import org.apache.tools.zip.ZipEntry;
import org.apache.tools.zip.ZipOutputStream，由于其存在方法out.setEncoding("gbk");//指定编码为gbk
6、ThreadLocal
finalThreadLocal threadLocal =newThreadLocal();
threadLocal.set("main--");
Thread thread = newThread() {
@Override
publicvoidrun() {
threadLocal.set("thread--");
Thread.yield();
System.out.println(Thread.currentThread().getName() + ":"+ threadLocal.get());
}
};
thread.start();
Thread.yield();
System.out.println(Thread.currentThread().getName() + ":"+ threadLocal.get());
7、数组和List之间的转换
数组->List: Arrays.asList(a)
List->数组:list.toArray()
8、正则表达式
(1)^：在[]内表示取反，在外面表示开头
(2)group
String regex ="[a-z]{3,5}";
Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher("Abc_defgh_aa_ABCD1");
while(matcher.find()) {
System.out.print("位置[左闭右开区间):"+matcher.start() +"_"+ matcher.end() +", 匹配内容:");
System.out.println(matcher.group());
}
测试结果:
位置[左闭右开区间):0_3, 匹配内容:Abc
位置[左闭右开区间):4_9, 匹配内容:defgh
位置[左闭右开区间):13_17, 匹配内容:ABCD
(3)邮件的正则表达式
[\\w[_.]]+@[\\w[_.]]+\\.[\\w]+
(4)"."点号在正则表达式中表示任何字符， 需要表示点号的时候必须转义\\.
(5)group的分组
分组是以正则表达式中的小括号'()'为标准的，当匹配成功后，group或group(0)表示匹配的整个字符串,group(1)代表正则中第一个小括号匹配到的内容,group(2)代表第二个小括号代表的内容，依次类推
(6)匹配require引入文件
"^[\\s]*#require[\\s]*\\(\"([\\w./]+)\"\\)[\\s]*$"含义为：以任意空白字符开头，在#require,再任意空白字符，再(",再任意字母、点号、斜线, 再"),最后任意个空白字符结尾
测试代码：
publicstaticvoidmain(String[] args) {
FileInputStream fileInputStream = null;
try{
fileInputStream = newFileInputStream(newFile(
"C:/Documents and Settings/***/My Documents/tmp/hello.js"));
} catch(FileNotFoundException e) {
e.printStackTrace();
}
InputStreamReader inputStreamReader = newInputStreamReader(fileInputStream,
Charset.defaultCharset());
BufferedReader bufferedReader = newBufferedReader(inputStreamReader);
String line = "";
try{
while((line = bufferedReader.readLine()) !=null) {
String requireFile = getRequireFile(line);
System.out.println(requireFile);
}
} catch(IOException e) {
e.printStackTrace();
} finally{
try{
bufferedReader.close();
inputStreamReader.close();
fileInputStream.close();
} catch(IOException e) {
e.printStackTrace();
}
}
}
privatestaticString getRequireFile(String line) {
String requireFile = "";
Pattern pattern = Pattern
.compile("^[\\s]*#require[\\s]*\\(\"([\\w./]+)\"\\)[\\s]*$", Pattern.MULTILINE);
Matcher matcher = pattern.matcher(line);
while(matcher.find()) {
requireFile = matcher.group(1);
}
returnrequireFile;
}
测试文件内容:
var param;
#require("hello/world_util/alibaba123_utils.js")
#require("/abc/world_util/alibaba12666_utils.js")
测试结果
hello/world_util/alibaba123_utils.js
/abc/world_util/alibaba12666_utils.js
9、FileReader有待完备的地方，只能使用系统默认的字符集，而没有提供传递字符集的构造函数
FileReader继承了InputStreamReader，但并没有实现父类中带字符集参数的构造函数，所以
FileReader只能按系统默认的字符集来解码
10、阻塞队列：BlockingQueue
生产者中的 put() 操作会在没有空间可用时阻塞，而消费者的 take() 操作会在队列中没有任何东西时阻塞。
11、信号量：Semaphore, 允许规定数量的线程进入操作，释放之后其他进入执行
Runnable limitedCall =newRunnable() {
finalRandom rand =newRandom();
finalSemaphore available =newSemaphore(3);
intcount =0;
publicvoidrun() {
inttime = rand.nextInt(15);
intnum = count++;
try{
available.acquire();
System.out.println("Executing "+"long-running action for "+ time
+ " seconds... #"+ num);
Thread.sleep(time * 1000);
System.out.println("Done with #"+ num +"!");
available.release();
} catch(InterruptedException intEx) {
intEx.printStackTrace();
}
}
};
for(inti =0; i <10; i++)
newThread(limitedCall).start();
12、死锁
publicclassDemo06 {
publicstaticvoidmain(String[] args) {
DeadLock deadLock1 = newDeadLock();
DeadLock deadLock2 = newDeadLock();
deadLock1.setFlag(true);
deadLock2.setFlag(false);
newThread(deadLock1).start();
newThread(deadLock2).start();
}
}
classDeadLockimplementsRunnable {
privatebooleanflag =false;
publicbooleanisFlag() {
returnflag;
}
publicvoidsetFlag(booleanflag) {
this.flag = flag;
}
privatestaticObject object1 =newObject();
privatestaticObject object2 =newObject();
publicvoidrun() {
if(flag) {
synchronized(object1) {
System.out.println(Thread.currentThread().getName() + " get object1.");
try{
Thread.sleep(1000);
} catch(InterruptedException e) {
e.printStackTrace();
}
synchronized(object2) {
System.out.println(Thread.currentThread().getName() + " get object2.");
}
}
} else{
synchronized(object2) {
System.out.println(Thread.currentThread().getName() + " get object2.");
try{
Thread.sleep(1000);
} catch(InterruptedException e) {
e.printStackTrace();
}
synchronized(object1) {
System.out.println(Thread.currentThread().getName() + " get object1.");
}
}
}
}
}
13、反射：通过classloader加载类，标准做法如下：
ClassLoader cl = Thread.currentThread().getContextClassLoader();
if (cl == null) cl = MyClass.class.getClassLoader(); // fallback
Class clazz = cl.loadClass(name);
14、文件大小限制
错误做法：
publicintgetFileSize(File f) {
longl = f.length();
return(int) l;
}
正确做法如下：
不支持传递超过2GB的文件. 最好的做法是对长度进行检查, 溢出时抛出异常
publicintgetFileSize(File f) {
longl = f.length();
if(l > Integer.MAX_VALUE)thrownewIllegalStateException("int overflow");
return(int) l;
}
15、线程sleep中断
try{
Thread.sleep(1000);
} catch(InterruptedException e) {
Thread.currentThread().interrupt();
}
or
while(true) {
if(Thread.currentThread().isInterrupted())break;
}
16、开发中常用术语解释
java的几种对象(PO,VO,DAO,BO,POJO)解释
一、PO:persistant object 持久对象,可以看成是与数据库中的表相映射的java对象。最简单的PO就是对应数据库中某个表中的一条记录，多个记录可以用PO的集合。PO中应该不包含任何对数据库的操作。
二、VO:value object值对象。通常用于业务层之间的数据传递，和PO一样也是仅仅包含数据而已。但应是抽象出的业务对象,可以和表对应,也可以不,这根据业务的需要.个人觉得同DTO(数据传输对象),在web上传递。
三、DAO:data access object 数据访问对象，此对象用于访问数据库。通常和PO结合使用，DAO中包含了各种数据库的操作方法。通过它的方法,结合PO对数据库进行相关的操作。
四、BO:business object 业务对象,封装业务逻辑的java对象,通过调用DAO方法,结合PO,VO进行业务操作。
五、POJO:plain ordinary java object 简单无规则java对象,我个人觉得它和其他不是一个层面上的东西,VO和PO应该都属于它。
17、多线售票系统：
classTicketSellerimplementsRunnable {
privateintticketCount =10;
@Override
publicvoidrun() {
while(ticketCount >0) {
synchronized(this) {
if(ticketCount >0) {
try{
Thread.sleep(100);
} catch(InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()
+ " sell ticket: "+ ticketCount--);
}
}
}
}
}
publicclassDemo01 {
publicstaticvoidmain(String[] args) {
TicketSeller ticketSeller = newTicketSeller();
newThread(ticketSeller,"Thread A").start();
newThread(ticketSeller,"Thread B").start();
newThread(ticketSeller,"Thread C").start();
newThread(ticketSeller,"Thread D").start();
}
}
测试结果：
Thread A sell ticket: 10
Thread A sell ticket: 9
Thread D sell ticket: 8
Thread D sell ticket: 7
Thread D sell ticket: 6
Thread C sell ticket: 5
Thread C sell ticket: 4
Thread C sell ticket: 3
Thread B sell ticket: 2
Thread B sell ticket: 1
18、中断处理
classTicketSellerimplementsRunnable {
@Override
publicvoidrun() {
try{
System.out.println("线程启动");
Thread.sleep(10000);
} catch(InterruptedException e) {
System.out.println("线程被中断");
// e.printStackTrace();
}
}
}
publicclassDemo01 {
publicstaticvoidmain(String[] args)throwsInterruptedException {
TicketSeller ticketSeller = newTicketSeller();
Thread thread = newThread(ticketSeller,"Thread A");
thread.start();
System.out.println("====主线程执行===");
Thread.sleep(1000);
// thread.interrupt();
System.out.println("线程被中断否："+ thread.isInterrupted());
thread.interrupt();
System.out.println("线程被中断否："+ thread.isInterrupted());
System.out.println("线程被中断否2："+ thread.isInterrupted());
System.out.println("主线程是否被中断："+ Thread.interrupted());
System.out.println("====主线程结束===");
}
}
测试结果：
====主线程执行===
线程启动
线程被中断否：false
线程被中断否：true
线程被中断否2：true
主线程是否被中断：false
线程被中断
====主线程结束===
结论：
interrupt中断该线程，isInterrupted检查该线程是否被中断，interrupted检查当前线程是否被中断。
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