Java IO(三)--字节流基本使用
I/O流分类：
InputStream和Read的子类都有read()，用来读取单个字节或字节数组
OutputStream和write的子类都有write()，用来写入单个字节或字节数组
一般都是通过装饰器Decorator模式叠加多个对象提供所期望的功能。创建单一的流，却需要创建多个对象
InputStream：
InputStream为字节输入流，一般都是通过其子类实现功能，是所有字节输入流的基类
public abstract class InputStream implements Closeable {
private static final int MAX_SKIP_BUFFER_SIZE = 2048;
public abstract int read() throws IOException; //读取1byte的数据，返回int类型。若返回值=-1说明没有读取到任何字节
public int read(byte[] var1) throws IOException {} //读取var1.length个字节的数据放到var1数组中，返回值是读取的字节数
public int read(byte[] var1, int off, int len) throws IOException {} //从输入流中最多读取len个字节的数据，存放到偏移量为off的var1数组中。
public long skip(long var1) throws IOException {} //忽略输入流中的n个字节，返回值是实际忽略的字节数, 跳过一些字节来读取
public int available() throws IOException {} //返回输入流中可以读取的字节数。必须是InputStream的子类调用才行，本身调用返回0
public void close() throws IOException {} //每次读取结束，都要关闭输入流并释放与流相关的资源
}
OutputStream：
OutputStream为字节输出流，一般都是通过其子类实现功能，是所有字节输出流的基类
public abstract class OutputStream implements Closeable, Flushable {
public OutputStream() {}
public abstract void write(int var1) throws IOException; //先将int转换为byte类型，把低字节写入到输出流中
public void write(byte[] var1) throws IOException {} //将数组var1中的字节写到输出流
public void write(byte[] var1, int off, int len) throws IOException {} //将数组var1的字节从偏移量off开始的len个字节写到输出流
public void flush() throws IOException { } //将数据缓冲区中数据全部输出，并清空缓冲区
public void close() throws IOException { } //每次写入结束，都要关闭输出流并释放与流相关的资源
}
FileInputStream和FileOutputStream：
public static void main(String[] args) throws IOException {
String pathName = "D:" + File.separator + "a.txt";
File file = new File(pathName);
OutputStream outputStream = new FileOutputStream(file);
outputStream.write("abc1".getBytes());
outputStream.close();
InputStream inputStream = new FileInputStream(file);
byte[] bytes = new byte[1024];
int length = inputStream.read(bytes);
String s = new String(bytes, 0, length);
System.out.println(s);
inputStream.close();
}
输出结果：
我是好人追加内容
FileOutputStream用来从内存区读数据到文件，如果文件存在，会把内容覆盖，如果不存在，创建文件，然后把数据写入
FileInputStream用来从文件读数据到内存区
ByteArrayInputStream和ByteArrayOutputStream：
ByteArrayOutputStream创建的时候，程序内部创建一个byte[]类型的缓冲区，然后向数组中写入或读出byte型数据。
public static void main(String[] args) throws IOException {
OutputStream outputStream = new ByteArrayOutputStream();
outputStream.write("abc".getBytes());
byte[] bytes = ((ByteArrayOutputStream) outputStream).toByteArray();
outputStream.close();
InputStream inputStream = new ByteArrayInputStream(bytes);
byte[] bytes1 = new byte[1024];
int len;
while ((len = inputStream.read(bytes1)) != -1) {
System.out.println(new String(bytes1, 0, len));
}
}
输出结果：abc
可以从得到byte[]缓冲区，然后读取数据，可以向缓冲区多次写入数据，然后集中一次读取
BufferedInputStream、BufferedInputStream：
public static void main(String[] args) throws IOException {
String pathName = "D:" + File.separator + "a.txt";
File file = new File(pathName);
BufferedInputStream inputStream = new BufferedInputStream(new FileInputStream(file));
BufferedOutputStream outputStream = new BufferedOutputStream(new FileOutputStream(new File("D:" + File.separator + "b.txt")));
byte[] bytes = new byte[4];
while (inputStream.read(bytes) != -1) {
System.out.println(new String(bytes));
outputStream.write(bytes);
}
inputStream.close();
outputStream.close();
}
在文件流外面包装一层缓冲流读取函数，先从缓冲区读取数据
PS：在写入缓冲区结束之后，一定要调用flush()或者close()，否则数据一致存在缓冲区，而没有写出
PipedInputStream、PipedOutputStream：
管道流主要用于连接两个线程的数据通信.通过连接而产生一个通信管道，PipedOutputStream向管道中写入数据，PipedInputStream从管
道中读取数据。管道输出流和管道输入流执行时不能互相阻塞,所以一般要开启独立线程分别执行
public class Sender implements Runnable{
private PipedOutputStream outputStream = new PipedOutputStream();
public PipedOutputStream outputStream() {
return this.outputStream;
}
@Override
public void run() {
try {
outputStream.write("message".getBytes());
outputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public class Receiver implements Runnable{
private PipedInputStream inputStream = new PipedInputStream();
public PipedInputStream inputStream() {
return this.inputStream;
}
@Override
public void run() {
byte[] bytes = new byte[1024];
try {
int len = inputStream.read(bytes);
if (len != -1) {
System.out.println("成功接收：" + new String(bytes));
}
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public class Test {
public static void main(String[] args) throws IOException {
Sender sender = new Sender();
Receiver receiver = new Receiver();
PipedOutputStream outputStream = sender.outputStream();
PipedInputStream inputStream = receiver.inputStream();
inputStream.connect(outputStream);
new Thread(sender).start();
new Thread(receiver).start();
}
}
输出结果：
成功接收：message
ObjectInputStream、ObjectOutputStream：
ObjectOutputStream可以把对象直接存入到文件中,然后利用ObjectInputStream读取文件还原成对象
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Student implements Serializable{
private int id;
private String name;
private int sex;
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
public static void main(String[] args) throws Exception {
String pathName = "D:" + File.separator + "a.txt";
File file = new File(pathName);
ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream(file));
Student student = new Student(1001, "sam", 1);
outputStream.writeObject(student);
outputStream.close();
ObjectInputStream inputStream = new ObjectInputStream(new FileInputStream(file));
Student student1 = (Student)inputStream.readObject();
System.out.println(student1);
}
PS：保存的对象必须实现了Serializable接口，否则出现异常：java.io.NotSerializableException: com.it.entity.Student
