java io 流

java io 流

io 流总览

io 流主要提供四个接口

InputStream
OutputStream
Reader
Writer

InputStream

InputStream 输入字节流，关注字节的读取，io 包提供如下 InputStream 的实现

ByteArrayInputStream
FileInputStream
PipedInputStream
DataInputStream
ObjectInputStream
BufferedInputStream
SequenceInputStream
PushbackInputStream

InputStream 提供如下接口:

read
read(buffer)
read(buffer, offset, length)
readNBytes(buffer, offset, length)
readAllBytes
skip
available
mark
reset
close

{
    InputStream in = new ByteArrayInputStream("0123456789".getBytes());
    assertEquals(in.read(), '0');
}
{
    InputStream in = new ByteArrayInputStream("0123456789".getBytes());
    byte[] buf = new byte[4];
    assertEquals(in.read(buf), 4);
    assertArrayEquals(buf, "0123".getBytes());
}
{
    InputStream in = new ByteArrayInputStream("0123456789".getBytes());
    byte[] buf = new byte[20];
    assertEquals(in.read(buf), 10);
    assertArrayEquals(Arrays.copyOf(buf, 10), "0123456789".getBytes());
}
{
    InputStream in = new ByteArrayInputStream("0123456789".getBytes());
    byte[] buf = new byte[20];
    assertEquals(in.read(buf, 1, 4), 4);
    assertArrayEquals(Arrays.copyOfRange(buf, 1, 1 + 4), "0123".getBytes());
}
{
    InputStream in = new ByteArrayInputStream("0123456789".getBytes());
    byte[] buf = new byte[20];
    assertEquals(in.readNBytes(buf, 1, 4), 4);
    assertArrayEquals(Arrays.copyOfRange(buf, 1, 1 + 4), "0123".getBytes());
}
{
    InputStream in = new ByteArrayInputStream("0123456789".getBytes());
    assertArrayEquals(in.readAllBytes(), "0123456789".getBytes());
}
{
    InputStream in = new ByteArrayInputStream("0123456789".getBytes());
    assertEquals(in.skip(2), 2);
    assertEquals(in.available(), 8);
    assertEquals(in.read(), '2');
    assertEquals(in.available(), 7);
    in.mark(0);
    assertEquals(in.read(), '3');
    in.reset();
    assertEquals(in.available(), 7);
    assertEquals(in.read(), '3');
    in.close();
}
{
    InputStream in = new ByteArrayInputStream("0123456789".getBytes());
    for (int ch = in.read(); ch != -1; ch = in.read()) {
        System.out.println(ch);
    }
}

OutputStream

OutputStream 输出字节流，关注字节的写入，io 包提供了如下 OutputStream 的实现

ByteArrayOutputStream
FileOutputStream
PipedOutputStream
DataOutputStream
ObjectOutputStream
BufferedOutputStream
SequenceOutputStream

OutputStream 提供如下接口:

write
write(buffer)
write(buffer, offset, length)
flush
close

OutputStream out = new ByteArrayOutputStream();
out.write('0');
out.write("123456789".getBytes());
out.write("0123456789".getBytes(), 1, 2);
out.flush();
out.close();

Reader

Reader 字符输入流，关注字符的读取，io 包提供如下 Reader 的实现

• CharArrayReader : 字符数组输入流
• FileReader : 文件字符输入流
• PipedReader : 管道输入流，可以和 PipedWriter 连接，通常用于线程间通信
• StringReader : 字符串输入流
• BufferedReader : 带缓冲 buffer 的字符输入流
• LineNumberReader : 带行号的字符输入流
• PushbackReader : 能回退的字符输入流
• InputStreamReader : 输入字节流转字符流

Reader 提供如下接口:

read
read(buffer)
read(buffer, offset, length)
read(CharBuffer
skip
mark
reset
close

{
    Reader reader = new CharArrayReader("0123456789".toCharArray());
    assertEquals(reader.read(), '0');
}
{
    Reader reader = new CharArrayReader("0123456789".toCharArray());
    char[] buf = new char[4];
    assertEquals(reader.read(buf), 4);
    assertArrayEquals(buf, "0123".toCharArray());
}
{
    Reader reader = new CharArrayReader("0123456789".toCharArray());
    char[] buf = new char[20];
    assertEquals(reader.read(buf), 10);
    assertArrayEquals(Arrays.copyOf(buf, 10), "0123456789".toCharArray());
}
{
    Reader reader = new CharArrayReader("0123456789".toCharArray());
    char[] buf = new char[20];
    assertEquals(reader.read(buf, 1, 4), 4);
    assertArrayEquals(Arrays.copyOfRange(buf, 1, 1 + 4), "0123".toCharArray());
}
{
    Reader reader = new CharArrayReader("0123456789".toCharArray());
    CharBuffer buf = CharBuffer.allocate(20);
    assertEquals(reader.read(buf), 10);
}
{
    Reader reader = new CharArrayReader("0123456789".toCharArray());
    assertTrue(reader.ready());
    assertEquals(reader.skip(2), 2);
    assertEquals(reader.read(), '2');
    reader.mark(0);
    assertEquals(reader.read(), '3');
    reader.reset();
    assertEquals(reader.read(), '3');
    reader.close();
}
{
    Reader reader = new CharArrayReader("0123456789".toCharArray());
    for (int ch = reader.read(); ch != -1; ch = reader.read()) {
        System.out.println(ch);
    }
}

Writer

Writer 字符输出流，关注字符的写入，io 包提供如下 Writer 的实现

• CharArrayWriter : 字符数组输出流
• FileWriter : 文件字符输出流
• PipedWriter : 管道输出流，可以和 PipedReader 连接，通常用于线程间通信
• StringWriter : 字符串输出流
• BufferedWriter : 带缓冲 buffer 的字符输出流
• OutputStreamWriter : 输出字节流转字符流

Writer 提供如下接口:

write(char)
write(string)
write(string, offset, length)
write(char[])
write(char[], offset, length)
append(ch)
append(CharSequence)
append(CharSequence, offset, length)
flush
close

Writer writer = new CharArrayWriter();
writer.write('0');
writer.write("0123456789");
writer.write("0123456789", 1, 4);
writer.write("0123456789".toCharArray());
writer.write("0123456789".toCharArray(), 1, 4);
writer.append('0');
writer.append(new StringBuilder("0123456789"));
writer.append(new StringBuilder("0123456789"), 1, 4);
writer.flush();
writer.close();

文件字节流

文件字节流关注文件的读取和写入

{
    FileOutputStream fout = new FileOutputStream("/tmp/test.txt");
    fout.write("No patient who, who has no wisdom".getBytes());
    fout.close();
}
{
    FileInputStream fin = new FileInputStream("/tmp/test.txt");
    assertArrayEquals(fin.readAllBytes(), "No patient who, who has no wisdom".getBytes());
    fin.close();
}

缓冲字节流

缓冲字节流采用装饰者模式，装饰在其他流上，使流拥有了缓存功能，从而提高读写了效率

{
    BufferedOutputStream bout = new BufferedOutputStream(new FileOutputStream("/tmp/test.txt"));
    bout.write("People lack the willpower, rather than strength".getBytes());
    bout.close();
}
{
    BufferedInputStream bin = new BufferedInputStream(new FileInputStream("/tmp/test.txt"));
    assertArrayEquals(bin.readAllBytes(), "People lack the willpower, rather than strength".getBytes());
    bin.close();
}

二进制字节流

二进制字节流关注在基本数据类型的读取和写入，采用装饰者模式，能装饰在其他流上

DataOutputStream 在 OutputStream 的基础上新增了如下接口:

writeBoolean
writeByte
writeShort
writeInt
writeLong
writeFloat
writeDouble
writeChar
writeUTF

DataInputStream 在 InputStream 的基础上新增了如下接口:

readBoolean
readByte
readShort
readInt
readLong
readFloat
readDouble
readChar
readUTF

{
    DataOutputStream dout = new DataOutputStream(new BufferedOutputStream(new FileOutputStream("/tmp/test.txt")));
    dout.writeBoolean(false);
    dout.writeByte('x');
    dout.writeShort(123);
    dout.writeInt(123456);
    dout.writeLong(123456789);
    dout.writeFloat((float) 123.456);
    dout.writeDouble(123.456);
    dout.writeUTF("Rome wasn’t built in one day");
    dout.close();
}
{
    DataInputStream din = new DataInputStream(new BufferedInputStream(new FileInputStream("/tmp/test.txt")));
    assertEquals(din.readBoolean(), false);
    assertEquals(din.readByte(), 'x');
    assertEquals(din.readShort(), 123);
    assertEquals(din.readInt(), 123456);
    assertEquals(din.readLong(), 123456789);
    assertEquals(din.readFloat(), (float) 123.456);
    assertEquals(din.readDouble(), 123.456);
    assertEquals(din.readUTF(), "Rome wasn’t built in one day");
    din.close();
}

对象字节流

对象字节流关注对象的写入和读取，同时拥有二进制字节流的所有功能，同样采用装饰者模式

ObjectOutputStream 相比 DataOutputStream 新增了如下接口:

• writeObject : 写入任何 Serializable 对象

ObjectInputStream 相比 DataInputStream 新增了如下接口:

• readObject : 从流中读取一个对象

{
    ObjectOutputStream oout = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream("/tmp/test.txt")));
    oout.writeBoolean(false);
    oout.writeByte('x');
    oout.writeShort(123);
    oout.writeInt(123456);
    oout.writeLong(123456789);
    oout.writeFloat((float) 123.456);
    oout.writeDouble(123.456);
    oout.writeUTF("Nothing is impossible to a willing heart");
    oout.writeObject(new Point(123, 456));
    oout.close();
}
{
    ObjectInputStream oin = new ObjectInputStream(new BufferedInputStream(new FileInputStream("/tmp/test.txt")));
    assertEquals(oin.readBoolean(), false);
    assertEquals(oin.readByte(), 'x');
    assertEquals(oin.readShort(), 123);
    assertEquals(oin.readInt(), 123456);
    assertEquals(oin.readLong(), 123456789);
    assertEquals(oin.readFloat(), (float) 123.456);
    assertEquals(oin.readDouble(), 123.456);
    assertEquals(oin.readUTF(), "Nothing is impossible to a willing heart");
    Point point = (Point) oin.readObject();
    assertEquals(point.x, 123);
    assertEquals(point.y, 456);
    oin.close();
}

回退字节流

可回退字节流内部维护了一个固定大小的缓冲区(可通过构造函数配置 buffer 的大小)，允许将字节回退到缓冲区，如果超过了缓冲区大小，会抛出异常

PushbackInputStream 在 InputStream 的基础上新增了如下接口:

unread
unread(buffer)
unread(buffer, offset, length)

PushbackInputStream pin = new PushbackInputStream(new ByteArrayInputStream("Failure is the mother of success".getBytes()), 10);
byte[] buf = new byte[7];
assertEquals(pin.read(buf), 7);
assertArrayEquals(buf, "Failure".getBytes());
pin.unread(buf);
assertEquals(pin.read(buf), 7);
assertArrayEquals(buf, "Failure".getBytes());
// 超过 buffer 的大小，抛出 IOException
assertThrows(IOException.class, () -> pin.unread("01234567890".getBytes()));

SequenceInputStream

SequenceInputStream 将多个 InputStream 合并成一个

InputStream in1 = new ByteArrayInputStream("For man is man and master of his fate/n".getBytes());
InputStream in2 = new ByteArrayInputStream("Cease to struggle and you cease to live/n".getBytes());
Vector<InputStream> vi = new Vector<>(List.of(in1, in2));
SequenceInputStream sin = new SequenceInputStream(vi.elements());
assertArrayEquals(sin.readAllBytes(), "For man is man and master of his fate/nCease to struggle and you cease to live/n".getBytes());

管道字节流

PipedInputStream 和 PipedOutputStream 通过调用 connect 方法建立连接，往 PipedOutputStream 写入，能从 PipedInputStream 读取，这种管道模式是一对一的，对一个管道流建立两次连接会抛出异常

PipedOutputStream 在 OutputStream 的基础上提供如下接口:

• connect : 与一个 PipedInputStream 建立连接，如果已经建立连接，将抛出异常

PipedInputStream 在 InputStream 的基础上提供如下接口:

• connect : 与一个 PipedOutputStream 建立连接，如果已经建立连接，将抛出异常

ExecutorService es = Executors.newCachedThreadPool();
PipedInputStream pin = new PipedInputStream();
PipedOutputStream pout = new PipedOutputStream();
pin.connect(pout);

es.execute(() -> {
    try {
        ObjectOutputStream oout = new ObjectOutputStream(pout);
        oout.writeInt(123456);
        oout.writeUTF("如果你还没能找到让自己热爱的事业，继续寻找，不要放弃");
        oout.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
});

es.execute(() -> {
    try {
        ObjectInputStream oin = new ObjectInputStream(pin);
        assertEquals(oin.readInt(), 123456);
        assertEquals(oin.readUTF(), "如果你还没能找到让自己热爱的事业，继续寻找，不要放弃");
        oin.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
});

try {
    es.shutdown();
    while (!es.awaitTermination(1000, TimeUnit.MILLISECONDS)) {
        // nothing to do
    }
} catch (Exception e) {
    e.printStackTrace();
}

文件字符流

文件字符流关注文件的读取和写入，使用默认的 utf-8 来编码

{
    FileWriter fw = new FileWriter("/tmp/test.txt");
    assertEquals(fw.getEncoding(), "UTF8");
    System.out.println(fw.getEncoding());
    fw.write("初学者的心态；拥有初学者的心态是件了不起的事情");
    fw.flush();
    fw.close();
}
{
    FileReader fr = new FileReader("/tmp/test.txt");
    assertEquals(fr.getEncoding(), "UTF8");
    StringBuilder sb = new StringBuilder();
    for (int ch = fr.read(); ch != -1; ch = fr.read()) {
        sb.append((char) ch);
    }
    assertEquals(sb.toString(), "初学者的心态；拥有初学者的心态是件了不起的事情");
    fr.close();
}

缓冲字符流

采用装饰者模式，装饰在其他字符流上，增加缓存功能，提高读写性能。 Files 提供了缓冲字符流的构造，可以指定编码

BufferedWriter 在 Writer 的基础上，新增了如下接口:

• newLine : 写入一个换行符

BufferedReader 在 Reader 的基础上，新增了如下接口:

• readLine : 读取一个行，如果没有新的行，返回 null
• lines : 返回一个 java.util.stream.Stream ，支持 java 8 的流式处理

{
    // BufferedWriter bw = new BufferedWriter(new FileWriter("/tmp/test.txt"));
    BufferedWriter bw = Files.newBufferedWriter(Paths.get("/tmp/test.txt"), Charsets.UTF_8);
    bw.write("穷则独善其身，达则兼济天下");
    bw.newLine();
    bw.write("玉不琢、不成器，人不学、不知义");
    bw.newLine();
    bw.close();
}
{
    // BufferedReader br = new BufferedReader(new FileReader("/tmp/test.txt"));
    BufferedReader br = Files.newBufferedReader(Paths.get("/tmp/test.txt"), Charsets.UTF_8);
    assertEquals(br.readLine(), "穷则独善其身，达则兼济天下");
    assertEquals(br.readLine(), "玉不琢、不成器，人不学、不知义");
    assertEquals(br.readLine(), null);
    br.close();
}
{
    // BufferedReader br = new BufferedReader(new FileReader("/tmp/test.txt"));
    BufferedReader br = Files.newBufferedReader(Paths.get("/tmp/test.txt"), Charsets.UTF_8);
    assertThat(br.lines().collect(Collectors.toList()), equalTo(List.of(
            "穷则独善其身，达则兼济天下",
            "玉不琢、不成器，人不学、不知义"
    )));
    br.close();
}

StreamReaderWriter

InputStreamReader 和 OutputStreamWriter 能将字节流转化字符流，还可以指定编码

{
    OutputStreamWriter ow = new OutputStreamWriter(new FileOutputStream("/tmp/test.txt"), "utf-8");
    ow.write("你究竟是想一辈子卖糖水，还是希望获得改变世界的机遇");
    ow.flush();
    ow.close();
}
{
    InputStreamReader rw = new InputStreamReader(new FileInputStream("/tmp/test.txt"), "utf-8");
    StringBuilder sb = new StringBuilder();
    for (int ch = rw.read(); ch != -1; ch = rw.read()) {
        sb.append((char) ch);
    }
    assertEquals(sb.toString(), "你究竟是想一辈子卖糖水，还是希望获得改变世界的机遇");
    rw.close();
}

字符串流

字符串构建的流

{
    StringWriter sw = new StringWriter();
    sw.write("学而不思则罔，思而不学则殆");
    assertEquals(sw.getBuffer().toString(), "学而不思则罔，思而不学则殆");
    sw.close();
}
{
    StringReader sr = new StringReader("一年之计在于春，一日之计在于晨");
    StringBuilder sb = new StringBuilder();
    for (int ch = sr.read(); ch != -1; ch = sr.read()) {
        sb.append((char) ch);
    }
    assertEquals(sb.toString(), "一年之计在于春，一日之计在于晨");
}

LineNumberReader

LineNumberReader 支持行号的字符流

LineNumberReader 在 Reader 的基础上，新增了如下接口:

setLineNumber
getLineNumber

{
    BufferedWriter bw = new BufferedWriter(new FileWriter("/tmp/test.txt"));
    bw.write("富贵不能淫/n贫贱不能移/n威武不能屈/n此之谓大丈夫/n");
    bw.close();
}
{
    LineNumberReader lr = new LineNumberReader(new BufferedReader(new FileReader("/tmp/test.txt")));
    List<String> lines = new LinkedList<>();
    for (String line = lr.readLine(); line != null; line = lr.readLine()) {
        lines.add(lr.getLineNumber() + " " + line);
    }
    assertThat(lines, equalTo(List.of(
            "1 富贵不能淫", "2 贫贱不能移", "3 威武不能屈", "4 此之谓大丈夫"
    )));
}

回退字符流

可回退字符流内部维护了一个固定大小的缓冲区(可通过构造函数配置 buffer 的大小)，允许将字符回退到缓冲区，如果超过了缓冲区大小，会抛出异常

PushbackReader 在 Reader 的基础上新增了如下接口:

unread
unread(cbar[])
unread(char[], offset, length)

PushbackReader pr = new PushbackReader(new StringReader("蚍蜉撼大树,可笑不自量"), 10);
char[] buf = new char[5];
assertEquals(pr.read(buf), 5);
assertArrayEquals(buf, "蚍蜉撼大树".toCharArray());
pr.unread(buf);
assertEquals(pr.read(buf), 5);
assertArrayEquals(buf, "蚍蜉撼大树".toCharArray());
// 超过 buffer 的大小，抛出 IOException
assertThrows(IOException.class, () -> pr.unread("01234567890".toCharArray()));

管道字符流

PipedReader 和 PipedWriter 通过调用 connect 方法建立连接，往 PipedWriter 写入，能从 PipedReader 读取，这种管道模式是一对一的，对一个管道流建立两次连接会抛出异常

PipedWriter 在 Writer 的基础上提供如下接口:

• connect : 与一个 PipedReader 建立连接，如果已经建立连接，将抛出异常

PipedReader 在 Reader 的基础上提供如下接口:

• connect : 与一个 PipedWriter 建立连接，如果已经建立连接，将抛出异常

ExecutorService es = Executors.newCachedThreadPool();
PipedReader pr = new PipedReader();
PipedWriter pw = new PipedWriter();
pr.connect(pw);

es.execute(() -> {
    try {
        BufferedWriter bw = new BufferedWriter(pw);
        bw.write("活着就是为了改变世界，难道还有其他原因吗");
        bw.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
});

es.execute(() -> {
    try {
        BufferedReader br = new BufferedReader(pr);
        assertEquals(br.readLine(), "活着就是为了改变世界，难道还有其他原因吗");
        br.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
});

try {
    es.shutdown();
    while (!es.awaitTermination(1000, TimeUnit.MILLISECONDS)) {
        // nothing to do
    }
} catch (Exception e) {
    e.printStackTrace();
}

链接

• 测试代码: https://github.com/hatlonely/...