Java IO流源码笔记
概览
Java中的IO源为4个抽象类，2个字节流相关抽象类InputStream,OutputStream. 2个字符流相关抽象类Reader,Writer.直接联系是都实现了Closeable接口，另外，整个IO的代码基于装饰者模式设计，存在大量的组合 > 聚合 > 关联 > 依赖关系，不了解UML模型图和关系的可以点击这里快速了解。我这里为了UML图的可读性，没有打开dependencies。有兴趣的读者可以自己使用IDEA的diagrams功能查看
除了抽象类Reader下面的FilterReader是抽象类，其他实现全部是非抽象类。包括缓冲Buffered,数据Data,文件File,字节数组ByteArray,Object,String等各种字节/字符流实现类
IO实现类中分为两类，一类是被装饰者类，一类是装饰者。被装饰者类就是能够从数据源获取数据的类，比如网络，文件，标准输入/输出等，另一类型是装饰者类，比如BufferedInputStream/BufferedOutputStream等，装饰者类中依赖一个数据源被装饰者类，来实现特定功能，比如缓冲的流读写等，体现在装饰者类的构造函数中需要传入一个被装饰的数据流
字节流抽象类约定的需实现的抽象方法read()返回的是int，即ASCII,而字符流约定需要实现的抽象方法为abstract public int read(char cbuf[], int off, int len) throws IOException;读取字符数据到字符数组cbuf中，返回读取到的字符数int
InputStream-被装饰者超类
package java.io;
/**
* 此类只有一个抽象方法 read() 所有继承此类的方法必须实现read()方法 用于从输入流中处理读取数据的过程
*/
public abstract class InputStream implements Closeable {
//顾名思义 最大可跳过的字节数
private static final int MAX_SKIP_BUFFER_SIZE = 2048;
/**
* Reads the next byte of data from the input stream. The value byte is
* returned as an int in the range 0 to
* 255. If no byte is available because the end of the stream
* has been reached, the value -1 is returned. This method
* blocks until input data is available, the end of the stream is detected,
* or an exception is thrown.
*
* A subclass must provide an implementation of this method.
*
* @return the next byte of data, or -1 if the end of the
* stream is reached.
* @exception IOException if an I/O error occurs.
* 从输入流读取下一个字节 返回0-255的int值 其实就是ASCII 这个方法的实现在输入数据到达前必须阻塞，检测到输入流结束或者抛出异常则此方法可以结束
*/
public abstract int read() throws IOException;
//读取一批数据到传入的数组b中
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
/**
* 源码这里一大堆注释 但是实现其实很简单
* 传入一个数组b，然后正常读取数据，把读出来的字节从off参数位置开始放，总共读取len个字节
*/
public int read(byte b[], int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException();
} else if (off < 0 || len < 0 || len > b.length - off) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
int c = read();
if (c == -1) {
return -1;
}
b[off] = (byte)c;
int i = 1;
try {
for (; i < len ; i++) {
c = read();
if (c == -1) {
break;
}
b[off + i] = (byte)c;
}
} catch (IOException ee) {
}
return i;
}
/**
* Skips over and discards n bytes of data from this input
* stream. The skip method may, for a variety of reasons, end
* up skipping over some smaller number of bytes, possibly 0.
* This may result from any of a number of conditions; reaching end of file
* before n bytes have been skipped is only one possibility.
* The actual number of bytes skipped is returned. If {@code n} is
* negative, the {@code skip} method for class {@code InputStream} always
* returns 0, and no bytes are skipped. Subclasses may handle the negative
* value differently.
*
*
The skip method of this class creates a
* byte array and then repeatedly reads into it until n bytes
* have been read or the end of the stream has been reached. Subclasses are
* encouraged to provide a more efficient implementation of this method.
* For instance, the implementation may depend on the ability to seek.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException if the stream does not support seek,
* or if some other I/O error occurs.
* 跳过并丢弃n个字节的数据 如果n是负数 则返回0不跳过 官方鼓励实现类用更高效的方法实现
*/
public long skip(long n) throws IOException {
long remaining = n;
int nr;
if (n <= 0) {
return 0;
}
int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
byte[] skipBuffer = new byte[size];
while (remaining > 0) {
//不能超过最大跳过大小
nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
//输入流已结束
if (nr < 0) {
break;
}
remaining -= nr;
}
return n - remaining;
}
/**
* Returns an estimate of the number of bytes that can be read (or
* skipped over) from this input stream without blocking by the next
* invocation of a method for this input stream. The next invocation
* might be the same thread or another thread. A single read or skip of this
* many bytes will not block, but may read or skip fewer bytes.
*
*
Note that while some implementations of {@code InputStream} will return
* the total number of bytes in the stream, many will not. It is
* never correct to use the return value of this method to allocate
* a buffer intended to hold all data in this stream.
*
*
A subclass' implementation of this method may choose to throw an
* {@link IOException} if this input stream has been closed by
* invoking the {@link #close()} method.
*
*
The {@code available} method for class {@code InputStream} always
* returns {@code 0}.
*
*
This method should be overridden by subclasses.
*
* @return an estimate of the number of bytes that can be read (or skipped
* over) from this input stream without blocking or {@code 0} when
* it reaches the end of the input stream.
* @exception IOException if an I/O error occurs.
*/
//返回可读字节数 子类应该实现
public int available() throws IOException {
return 0;
}
/**
* Closes this input stream and releases any system resources associated
* with the stream.
*
*
The close method of InputStream does
* nothing.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {}
/**
* Marks the current position in this input stream. A subsequent call to
* the reset method repositions this stream at the last marked
* position so that subsequent reads re-read the same bytes.
*
*
The readlimit arguments tells this input stream to
* allow that many bytes to be read before the mark position gets
* invalidated.
*
*
The general contract of mark is that, if the method
* markSupported returns true, the stream somehow
* remembers all the bytes read after the call to mark and
* stands ready to supply those same bytes again if and whenever the method
* reset is called. However, the stream is not required to
* remember any data at all if more than readlimit bytes are
* read from the stream before reset is called.
*
*
Marking a closed stream should not have any effect on the stream.
*
*
The mark method of InputStream does
* nothing.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see java.io.InputStream#reset()
*/
//可以标记并用reset方法跳回去的一个预定义方法
public synchronized void mark(int readlimit) {}
/**
* Repositions this stream to the position at the time the
* mark method was last called on this input stream.
*
*
The general contract of reset is:
*
*
* - If the method
markSupported returns
* true, then:
*
* - If the method
mark has not been called since
* the stream was created, or the number of bytes read from the stream
* since mark was last called is larger than the argument
* to mark at that last call, then an
* IOException might be thrown.
*
* - If such an
IOException is not thrown, then the
* stream is reset to a state such that all the bytes read since the
* most recent call to mark (or since the start of the
* file, if mark has not been called) will be resupplied
* to subsequent callers of the read method, followed by
* any bytes that otherwise would have been the next input data as of
* the time of the call to reset.
*
* - If the method
markSupported returns
* false, then:
*
* - The call to
reset may throw an
* IOException.
*
* - If an
IOException is not thrown, then the stream
* is reset to a fixed state that depends on the particular type of the
* input stream and how it was created. The bytes that will be supplied
* to subsequent callers of the read method depend on the
* particular type of the input stream.
*
* The method reset for class InputStream
* does nothing except throw an IOException.
*
* @exception IOException if this stream has not been marked or if the
* mark has been invalidated.
* @see java.io.InputStream#mark(int)
* @see java.io.IOException
*/
public synchronized void reset() throws IOException {
throw new IOException("mark/reset not supported");
}
/**
* Tests if this input stream supports the mark and
* reset methods. Whether or not mark and
* reset are supported is an invariant property of a
* particular input stream instance. The markSupported method
* of InputStream returns false.
*
* @return true if this stream instance supports the mark
* and reset methods; false otherwise.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return false;
}
}
FilterInputStream-装饰者超类
package java.io;
/**
* A FilterInputStream contains
* some other input stream, which it uses as
* its basic source of data, possibly transforming
* the data along the way or providing additional
* functionality. The class FilterInputStream
* itself simply overrides all methods of
* InputStream with versions that
* pass all requests to the contained input
* stream. Subclasses of FilterInputStream
* may further override some of these methods
* and may also provide additional methods
* and fields.
*
* @author Jonathan Payne
* @since JDK1.0
* 此类包含一些其他的被装饰者的InputStream，用被装饰者的输入流数据作为基础数据，此类几乎没有干什么事儿 只是把被装饰者的依赖关系包进来了 掉用的都是传入进来的被装饰者的方法
*/
public
class FilterInputStream extends InputStream {
/**
* 被装饰者 需要被过滤的输入流 读取方法调用的是传入的in的读取方法
*/
protected volatile InputStream in;
protected FilterInputStream(InputStream in) {
this.in = in;
}
public int read() throws IOException {
return in.read();
}
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
public int read(byte b[], int off, int len) throws IOException {
return in.read(b, off, len);
}
public long skip(long n) throws IOException {
return in.skip(n);
}
public int available() throws IOException {
return in.available();
}
public void close() throws IOException {
in.close();
}
public synchronized void mark(int readlimit) {
in.mark(readlimit);
}
public synchronized void reset() throws IOException {
in.reset();
}
public boolean markSupported() {
return in.markSupported();
}
}
ByteArrayInputStream-被装饰者的字节数组输入流实现
package java.io;
/**
* A ByteArrayInputStream contains
* an internal buffer that contains bytes that
* may be read from the stream. An internal
* counter keeps track of the next byte to
* be supplied by the read method.
*
* Closing a ByteArrayInputStream has no effect. The methods in
* this class can be called after the stream has been closed without
* generating an IOException.
*
* @author Arthur van Hoff
* @see java.io.StringBufferInputStream
* @since JDK1.0
* 此实现包含一个内部的字节数组缓冲，用来读取数据流
*/
public
class ByteArrayInputStream extends InputStream {
/**
* An array of bytes that was provided
* by the creator of the stream. Elements buf[0]
* through buf[count-1] are the
* only bytes that can ever be read from the
* stream; element buf[pos] is
* the next byte to be read.
* 用于读取输入流的字节数组
*/
protected byte buf[];
/**
* The index of the next character to read from the input stream buffer.
* This value should always be nonnegative
* and not larger than the value of count.
* The next byte to be read from the input stream buffer
* will be buf[pos].
* 下一个待读数组位置
*/
protected int pos;
/**
* The currently marked position in the stream.
* ByteArrayInputStream objects are marked at position zero by
* default when constructed. They may be marked at another
* position within the buffer by the mark() method.
* The current buffer position is set to this point by the
* reset() method.
*
* If no mark has been set, then the value of mark is the offset
* passed to the constructor (or 0 if the offset was not supplied).
*
* @since JDK1.1
* 标记回朔地址
*/
protected int mark = 0;
/**
* The index one greater than the last valid character in the input
* stream buffer.
* This value should always be nonnegative
* and not larger than the length of buf.
* It is one greater than the position of
* the last byte within buf that
* can ever be read from the input stream buffer.
* 比有效字符(可读取字符)大的索引，默认为数组长度
*/
protected int count;
/**
* Creates a ByteArrayInputStream
* so that it uses buf as its
* buffer array.
* The buffer array is not copied.
* The initial value of pos
* is 0 and the initial value
* of count is the length of
* buf.
*
* @param buf the input buffer.
*/
public ByteArrayInputStream(byte buf[]) {
this.buf = buf;
this.pos = 0;
this.count = buf.length;
}
/**
* Creates ByteArrayInputStream
* that uses buf as its
* buffer array. The initial value of pos
* is offset and the initial value
* of count is the minimum of offset+length
* and buf.length.
* The buffer array is not copied. The buffer's mark is
* set to the specified offset.
*
* @param buf the input buffer.
* @param offset the offset in the buffer of the first byte to read.
* @param length the maximum number of bytes to read from the buffer.
*/
public ByteArrayInputStream(byte buf[], int offset, int length) {
this.buf = buf;
this.pos = offset;
this.count = Math.min(offset + length, buf.length);
this.mark = offset;
}
/**
* Reads the next byte of data from this input stream. The value
* byte is returned as an int in the range
* 0 to 255. If no byte is available
* because the end of the stream has been reached, the value
* -1 is returned.
*
* This read method
* cannot block.
*
* @return the next byte of data, or -1 if the end of the
* stream has been reached.
* 这里主要有个0xFF 不知道为何要如此使用？ TODO
*/
public synchronized int read() {
return (pos < count) ? (buf[pos++] & 0xff) : -1;
}
/**
* Reads up to len bytes of data into an array of bytes
* from this input stream.
* If pos equals count,
* then -1 is returned to indicate
* end of file. Otherwise, the number k
* of bytes read is equal to the smaller of
* len and count-pos.
* If k is positive, then bytes
* buf[pos] through buf[pos+k-1]
* are copied into b[off] through
* b[off+k-1] in the manner performed
* by System.arraycopy. The
* value k is added into pos
* and k is returned.
*
* This read method cannot block.
*
* @param b the buffer into which the data is read.
* @param off the start offset in the destination array b
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* -1 if there is no more data because the end of
* the stream has been reached.
* @exception NullPointerException If b is null.
* @exception IndexOutOfBoundsException If off is negative,
* len is negative, or len is greater than
* b.length - off
* 按量读取 使用System.arraycopy来进行实现
*/
public synchronized int read(byte b[], int off, int len) {
if (b == null) {
throw new NullPointerException();
} else if (off < 0 || len < 0 || len > b.length - off) {
throw new IndexOutOfBoundsException();
}
if (pos >= count) {
return -1;
}
int avail = count - pos;
if (len > avail) {
len = avail;
}
if (len <= 0) {
return 0;
}
System.arraycopy(buf, pos, b, off, len);
pos += len;
return len;
}
/**
* Skips n bytes of input from this input stream. Fewer
* bytes might be skipped if the end of the input stream is reached.
* The actual number k
* of bytes to be skipped is equal to the smaller
* of n and count-pos.
* The value k is added into pos
* and k is returned.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* 跳过的实现 直接移动指针位置pos
*/
public synchronized long skip(long n) {
long k = count - pos;
if (n < k) {
k = n < 0 ? 0 : n;
}
pos += k;
return k;
}
/**
* Returns the number of remaining bytes that can be read (or skipped over)
* from this input stream.
*
* The value returned is count - pos,
* which is the number of bytes remaining to be read from the input buffer.
*
* @return the number of remaining bytes that can be read (or skipped
* over) from this input stream without blocking.
*/
public synchronized int available() {
return count - pos;
}
/**
* Tests if this InputStream supports mark/reset. The
* markSupported method of ByteArrayInputStream
* always returns true.
*
* @since JDK1.1
*/
public boolean markSupported() {
return true;
}
/**
* Set the current marked position in the stream.
* ByteArrayInputStream objects are marked at position zero by
* default when constructed. They may be marked at another
* position within the buffer by this method.
*
* If no mark has been set, then the value of the mark is the
* offset passed to the constructor (or 0 if the offset was not
* supplied).
*
*
Note: The readAheadLimit for this class
* has no meaning.
*
* @since JDK1.1
*/
public void mark(int readAheadLimit) {
mark = pos;
}
/**
* Resets the buffer to the marked position. The marked position
* is 0 unless another position was marked or an offset was specified
* in the constructor.
*/
public synchronized void reset() {
pos = mark;
}
/**
* Closing a ByteArrayInputStream has no effect. The methods in
* this class can be called after the stream has been closed without
* generating an IOException.
*/
public void close() throws IOException {
}
}
BufferedInputStream-装饰者
package java.io;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
* A BufferedInputStream adds
* functionality to another input stream-namely,
* the ability to buffer the input and to
* support the mark and reset
* methods. When the BufferedInputStream
* is created, an internal buffer array is
* created. As bytes from the stream are read
* or skipped, the internal buffer is refilled
* as necessary from the contained input stream,
* many bytes at a time. The mark
* operation remembers a point in the input
* stream and the reset operation
* causes all the bytes read since the most
* recent mark operation to be
* reread before new bytes are taken from
* the contained input stream.
*
* @author Arthur van Hoff
* @since JDK1.0
* 装饰类 主要在InputStream的基础上 使用一个byte[]来使用缓冲区进行读取
* 操作的单位从原始类的字节 可以灵活的操作缓冲区数据
*/
public
class BufferedInputStream extends FilterInputStream {
//顾名思义 默认缓冲区大小
private static int DEFAULT_BUFFER_SIZE = 8192;
/**
* The maximum size of array to allocate.
* Some VMs reserve some header words in an array.
* Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
* 最大缓冲区大小 受限于某些VM的数组内存分配策略
*/
private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
/**
* The internal buffer array where the data is stored. When necessary,
* it may be replaced by another array of
* a different size.
* 核心缓冲数组
*/
protected volatile byte buf[];
/**
* Atomic updater to provide compareAndSet for buf. This is
* necessary because closes can be asynchronous. We use nullness
* of buf[] as primary indicator that this stream is closed. (The
* "in" field is also nulled out on close.)
* 保证buf缓冲区的原子操作性
*/
private static final
AtomicReferenceFieldUpdater bufUpdater =
AtomicReferenceFieldUpdater.newUpdater
(BufferedInputStream.class, byte[].class, "buf");
/**
* The index one greater than the index of the last valid byte in
* the buffer.
* This value is always
* in the range 0 through buf.length;
* elements buf[0] through buf[count-1]
* contain buffered input data obtained
* from the underlying input stream.
*/
protected int count;
/**
* The current position in the buffer. This is the index of the next
* character to be read from the buf array.
*
* This value is always in the range 0
* through count. If it is less
* than count, then buf[pos]
* is the next byte to be supplied as input;
* if it is equal to count, then
* the next read or skip
* operation will require more bytes to be
* read from the contained input stream.
*
* @see java.io.BufferedInputStream#buf
*/
protected int pos;
/**
* The value of the pos field at the time the last
* mark method was called.
*
* This value is always
* in the range -1 through pos.
* If there is no marked position in the input
* stream, this field is -1. If
* there is a marked position in the input
* stream, then buf[markpos]
* is the first byte to be supplied as input
* after a reset operation. If
* markpos is not -1,
* then all bytes from positions buf[markpos]
* through buf[pos-1] must remain
* in the buffer array (though they may be
* moved to another place in the buffer array,
* with suitable adjustments to the values
* of count, pos,
* and markpos); they may not
* be discarded unless and until the difference
* between pos and markpos
* exceeds marklimit.
*
* @see java.io.BufferedInputStream#mark(int)
* @see java.io.BufferedInputStream#pos
*/
protected int markpos = -1;
/**
* The maximum read ahead allowed after a call to the
* mark method before subsequent calls to the
* reset method fail.
* Whenever the difference between pos
* and markpos exceeds marklimit,
* then the mark may be dropped by setting
* markpos to -1.
*
* @see java.io.BufferedInputStream#mark(int)
* @see java.io.BufferedInputStream#reset()
*/
protected int marklimit;
/**
* Check to make sure that underlying input stream has not been
* nulled out due to close; if not return it;
*/
private InputStream getInIfOpen() throws IOException {
InputStream input = in;
if (input == null)
throw new IOException("Stream closed");
return input;
}
/**
* Check to make sure that buffer has not been nulled out due to
* close; if not return it;
*/
private byte[] getBufIfOpen() throws IOException {
byte[] buffer = buf;
if (buffer == null)
throw new IOException("Stream closed");
return buffer;
}
/**
* Creates a BufferedInputStream
* and saves its argument, the input stream
* in, for later use. An internal
* buffer array is created and stored in buf.
*
* @param in the underlying input stream.
*/
public BufferedInputStream(InputStream in) {
this(in, DEFAULT_BUFFER_SIZE);
}
/**
* Creates a BufferedInputStream
* with the specified buffer size,
* and saves its argument, the input stream
* in, for later use. An internal
* buffer array of length size
* is created and stored in buf.
*
* @param in the underlying input stream.
* @param size the buffer size.
* @exception IllegalArgumentException if {@code size <= 0}.
*/
public BufferedInputStream(InputStream in, int size) {
super(in);
if (size <= 0) {
throw new IllegalArgumentException("Buffer size <= 0");
}
buf = new byte[size];
}
/**
* Fills the buffer with more data, taking into account
* shuffling and other tricks for dealing with marks.
* Assumes that it is being called by a synchronized method.
* This method also assumes that all data has already been read in,
* hence pos > count.
* 从原始输入流往缓冲区填充数据
*/
private void fill() throws IOException {
byte[] buffer = getBufIfOpen();
if (markpos < 0)
pos = 0; /* no mark: throw away the buffer */
else if (pos >= buffer.length) /* no room left in buffer */
if (markpos > 0) { /* can throw away early part of the buffer */
int sz = pos - markpos;
System.arraycopy(buffer, markpos, buffer, 0, sz);
pos = sz;
markpos = 0;
} else if (buffer.length >= marklimit) {
markpos = -1; /* buffer got too big, invalidate mark */
pos = 0; /* drop buffer contents */
} else if (buffer.length >= MAX_BUFFER_SIZE) {
throw new OutOfMemoryError("Required array size too large");
} else { /* grow buffer */
int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?
pos * 2 : MAX_BUFFER_SIZE;
if (nsz > marklimit)
nsz = marklimit;
byte nbuf[] = new byte[nsz];
System.arraycopy(buffer, 0, nbuf, 0, pos);
if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
// Can't replace buf if there was an async close.
// Note: This would need to be changed if fill()
// is ever made accessible to multiple threads.
// But for now, the only way CAS can fail is via close.
// assert buf == null;
throw new IOException("Stream closed");
}
buffer = nbuf;
}
count = pos;
int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
if (n > 0)
count = n + pos;
}
/**
* See
* the general contract of the read
* method of InputStream.
*
* @return the next byte of data, or -1 if the end of the
* stream is reached.
* @exception IOException if this input stream has been closed by
* invoking its {@link #close()} method,
* or an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public synchronized int read() throws IOException {
if (pos >= count) {
fill();
if (pos >= count)
return -1;
}
return getBufIfOpen()[pos++] & 0xff;
}
/**
* Read characters into a portion of an array, reading from the underlying
* stream at most once if necessary.
*/
private int read1(byte[] b, int off, int len) throws IOException {
int avail = count - pos;
if (avail <= 0) {
/* If the requested length is at least as large as the buffer, and
if there is no mark/reset activity, do not bother to copy the
bytes into the local buffer. In this way buffered streams will
cascade harmlessly. */
if (len >= getBufIfOpen().length && markpos < 0) {
return getInIfOpen().read(b, off, len);
}
fill();
avail = count - pos;
if (avail <= 0) return -1;
}
int cnt = (avail < len) ? avail : len;
System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
pos += cnt;
return cnt;
}
/**
* Reads bytes from this byte-input stream into the specified byte array,
* starting at the given offset.
*
*
This method implements the general contract of the corresponding
* {@link InputStream#read(byte[], int, int) read} method of
* the {@link InputStream} class. As an additional
* convenience, it attempts to read as many bytes as possible by repeatedly
* invoking the read method of the underlying stream. This
* iterated read continues until one of the following
* conditions becomes true:
*
* - The specified number of bytes have been read,
*
*
- The
read method of the underlying stream returns
* -1, indicating end-of-file, or
*
* - The
available method of the underlying stream
* returns zero, indicating that further input requests would block.
*
*
If the first read on the underlying stream returns
* -1 to indicate end-of-file then this method returns
* -1. Otherwise this method returns the number of bytes
* actually read.
*
* Subclasses of this class are encouraged, but not required, to
* attempt to read as many bytes as possible in the same fashion.
*
* @param b destination buffer.
* @param off offset at which to start storing bytes.
* @param len maximum number of bytes to read.
* @return the number of bytes read, or -1 if the end of
* the stream has been reached.
* @exception IOException if this input stream has been closed by
* invoking its {@link #close()} method,
* or an I/O error occurs.
*/
public synchronized int read(byte b[], int off, int len)
throws IOException
{
getBufIfOpen(); // Check for closed stream
if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
int n = 0;
for (;;) {
int nread = read1(b, off + n, len - n);
if (nread <= 0)
return (n == 0) ? nread : n;
n += nread;
if (n >= len)
return n;
// if not closed but no bytes available, return
InputStream input = in;
if (input != null && input.available() <= 0)
return n;
}
}
/**
* See the general contract of the skip
* method of InputStream.
*
* @exception IOException if the stream does not support seek,
* or if this input stream has been closed by
* invoking its {@link #close()} method, or an
* I/O error occurs.
*/
public synchronized long skip(long n) throws IOException {
getBufIfOpen(); // Check for closed stream
if (n <= 0) {
return 0;
}
long avail = count - pos;
if (avail <= 0) {
// If no mark position set then don't keep in buffer
if (markpos <0)
return getInIfOpen().skip(n);
// Fill in buffer to save bytes for reset
fill();
avail = count - pos;
if (avail <= 0)
return 0;
}
long skipped = (avail < n) ? avail : n;
pos += skipped;
return skipped;
}
/**
* Returns an estimate of the number of bytes that can be read (or
* skipped over) from this input stream without blocking by the next
* invocation of a method for this input stream. The next invocation might be
* the same thread or another thread. A single read or skip of this
* many bytes will not block, but may read or skip fewer bytes.
*
* This method returns the sum of the number of bytes remaining to be read in
* the buffer (count - pos) and the result of calling the
* {@link java.io.FilterInputStream#in in}.available().
*
* @return an estimate of the number of bytes that can be read (or skipped
* over) from this input stream without blocking.
* @exception IOException if this input stream has been closed by
* invoking its {@link #close()} method,
* or an I/O error occurs.
*/
public synchronized int available() throws IOException {
int n = count - pos;
int avail = getInIfOpen().available();
return n > (Integer.MAX_VALUE - avail)
? Integer.MAX_VALUE
: n + avail;
}
/**
* See the general contract of the mark
* method of InputStream.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see java.io.BufferedInputStream#reset()
*/
public synchronized void mark(int readlimit) {
marklimit = readlimit;
markpos = pos;
}
/**
* See the general contract of the reset
* method of InputStream.
*
* If markpos is -1
* (no mark has been set or the mark has been
* invalidated), an IOException
* is thrown. Otherwise, pos is
* set equal to markpos.
*
* @exception IOException if this stream has not been marked or,
* if the mark has been invalidated, or the stream
* has been closed by invoking its {@link #close()}
* method, or an I/O error occurs.
* @see java.io.BufferedInputStream#mark(int)
*/
public synchronized void reset() throws IOException {
getBufIfOpen(); // Cause exception if closed
if (markpos < 0)
throw new IOException("Resetting to invalid mark");
pos = markpos;
}
/**
* Tests if this input stream supports the mark
* and reset methods. The markSupported
* method of BufferedInputStream returns
* true.
*
* @return a boolean indicating if this stream type supports
* the mark and reset methods.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return true;
}
/**
* Closes this input stream and releases any system resources
* associated with the stream.
* Once the stream has been closed, further read(), available(), reset(),
* or skip() invocations will throw an IOException.
* Closing a previously closed stream has no effect.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {
byte[] buffer;
while ( (buffer = buf) != null) {
if (bufUpdater.compareAndSet(this, buffer, null)) {
InputStream input = in;
in = null;
if (input != null)
input.close();
return;
}
// Else retry in case a new buf was CASed in fill()
}
}
}
FileInputStream-从文件读书数据的流
package java.io;
import java.nio.channels.FileChannel;
import sun.nio.ch.FileChannelImpl;
//此类的读取实现和一些其他操作 多依赖于c/c++的native本地方法实现
public
class FileInputStream extends InputStream
{
/* File Descriptor - handle to the open file */
//文件描述句柄
private final FileDescriptor fd;
/**
* The path of the referenced file
* (null if the stream is created with a file descriptor)
*/
//文件路径
private final String path;
private FileChannel channel = null;
//关闭锁对象
private final Object closeLock = new Object();
private volatile boolean closed = false;
/**
* Creates a FileInputStream by
* opening a connection to an actual file,
* the file named by the path name name
* in the file system. A new FileDescriptor
* object is created to represent this file
* connection.
*
* First, if there is a security
* manager, its checkRead method
* is called with the name argument
* as its argument.
*
* If the named file does not exist, is a directory rather than a regular
* file, or for some other reason cannot be opened for reading then a
* FileNotFoundException is thrown.
*
* @param name the system-dependent file name.
* @exception FileNotFoundException if the file does not exist,
* is a directory rather than a regular file,
* or for some other reason cannot be opened for
* reading.
* @exception SecurityException if a security manager exists and its
* checkRead method denies read access
* to the file.
* @see java.lang.SecurityManager#checkRead(java.lang.String)
* 打开一个文件连接
*/
public FileInputStream(String name) throws FileNotFoundException {
this(name != null ? new File(name) : null);
}
/**
* Creates a FileInputStream by
* opening a connection to an actual file,
* the file named by the File
* object file in the file system.
* A new FileDescriptor object
* is created to represent this file connection.
*
* First, if there is a security manager,
* its checkRead method is called
* with the path represented by the file
* argument as its argument.
*
* If the named file does not exist, is a directory rather than a regular
* file, or for some other reason cannot be opened for reading then a
* FileNotFoundException is thrown.
*
* @param file the file to be opened for reading.
* @exception FileNotFoundException if the file does not exist,
* is a directory rather than a regular file,
* or for some other reason cannot be opened for
* reading.
* @exception SecurityException if a security manager exists and its
* checkRead method denies read access to the file.
* @see java.io.File#getPath()
* @see java.lang.SecurityManager#checkRead(java.lang.String)
*/
public FileInputStream(File file) throws FileNotFoundException {
String name = (file != null ? file.getPath() : null);
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkRead(name);
}
if (name == null) {
throw new NullPointerException();
}
if (file.isInvalid()) {
throw new FileNotFoundException("Invalid file path");
}
fd = new FileDescriptor();
fd.attach(this);
path = name;
open(name);
}
/**
* Creates a FileInputStream by using the file descriptor
* fdObj, which represents an existing connection to an
* actual file in the file system.
*
* If there is a security manager, its checkRead method is
* called with the file descriptor fdObj as its argument to
* see if it's ok to read the file descriptor. If read access is denied
* to the file descriptor a SecurityException is thrown.
*
* If fdObj is null then a NullPointerException
* is thrown.
*
* This constructor does not throw an exception if fdObj
* is {@link java.io.FileDescriptor#valid() invalid}.
* However, if the methods are invoked on the resulting stream to attempt
* I/O on the stream, an IOException is thrown.
*
* @param fdObj the file descriptor to be opened for reading.
* @throws SecurityException if a security manager exists and its
* checkRead method denies read access to the
* file descriptor.
* @see SecurityManager#checkRead(java.io.FileDescriptor)
*/
public FileInputStream(FileDescriptor fdObj) {
SecurityManager security = System.getSecurityManager();
if (fdObj == null) {
throw new NullPointerException();
}
if (security != null) {
security.checkRead(fdObj);
}
fd = fdObj;
path = null;
/*
* FileDescriptor is being shared by streams.
* Register this stream with FileDescriptor tracker.
*/
fd.attach(this);
}
/**
* Opens the specified file for reading.
* @param name the name of the file
*/
private native void open0(String name) throws FileNotFoundException;
// wrap native call to allow instrumentation
/**
* Opens the specified file for reading.
* @param name the name of the file
*/
private void open(String name) throws FileNotFoundException {
open0(name);
}
/**
* Reads a byte of data from this input stream. This method blocks
* if no input is yet available.
*
* @return the next byte of data, or -1 if the end of the
* file is reached.
* @exception IOException if an I/O error occurs.
* read调用的read0调用的本地读取方法
*/
public int read() throws IOException {
return read0();
}
private native int read0() throws IOException;
/**
* Reads a subarray as a sequence of bytes.
* @param b the data to be written
* @param off the start offset in the data
* @param len the number of bytes that are written
* @exception IOException If an I/O error has occurred.
*/
private native int readBytes(byte b[], int off, int len) throws IOException;
/**
* Reads up to b.length bytes of data from this input
* stream into an array of bytes. This method blocks until some input
* is available.
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* -1 if there is no more data because the end of
* the file has been reached.
* @exception IOException if an I/O error occurs.
*/
public int read(byte b[]) throws IOException {
return readBytes(b, 0, b.length);
}
/**
* Reads up to len bytes of data from this input stream
* into an array of bytes. If len is not zero, the method
* blocks until some input is available; otherwise, no
* bytes are read and 0 is returned.
*
* @param b the buffer into which the data is read.
* @param off the start offset in the destination array b
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* -1 if there is no more data because the end of
* the file has been reached.
* @exception NullPointerException If b is null.
* @exception IndexOutOfBoundsException If off is negative,
* len is negative, or len is greater than
* b.length - off
* @exception IOException if an I/O error occurs.
*/
public int read(byte b[], int off, int len) throws IOException {
return readBytes(b, off, len);
}
/**
* Skips over and discards n bytes of data from the
* input stream.
*
*
The skip method may, for a variety of
* reasons, end up skipping over some smaller number of bytes,
* possibly 0. If n is negative, the method
* will try to skip backwards. In case the backing file does not support
* backward skip at its current position, an IOException is
* thrown. The actual number of bytes skipped is returned. If it skips
* forwards, it returns a positive value. If it skips backwards, it
* returns a negative value.
*
*
This method may skip more bytes than what are remaining in the
* backing file. This produces no exception and the number of bytes skipped
* may include some number of bytes that were beyond the EOF of the
* backing file. Attempting to read from the stream after skipping past
* the end will result in -1 indicating the end of the file.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException if n is negative, if the stream does not
* support seek, or if an I/O error occurs.
*/
public native long skip(long n) throws IOException;
/**
* Returns an estimate of the number of remaining bytes that can be read (or
* skipped over) from this input stream without blocking by the next
* invocation of a method for this input stream. Returns 0 when the file
* position is beyond EOF. The next invocation might be the same thread
* or another thread. A single read or skip of this many bytes will not
* block, but may read or skip fewer bytes.
*
*
In some cases, a non-blocking read (or skip) may appear to be
* blocked when it is merely slow, for example when reading large
* files over slow networks.
*
* @return an estimate of the number of remaining bytes that can be read
* (or skipped over) from this input stream without blocking.
* @exception IOException if this file input stream has been closed by calling
* {@code close} or an I/O error occurs.
*/
public native int available() throws IOException;
/**
* Closes this file input stream and releases any system resources
* associated with the stream.
*
*
If this stream has an associated channel then the channel is closed
* as well.
*
* @exception IOException if an I/O error occurs.
*
* @revised 1.4
* @spec JSR-51
*/
public void close() throws IOException {
synchronized (closeLock) {
if (closed) {
return;
}
closed = true;
}
if (channel != null) {
channel.close();
}
fd.closeAll(new Closeable() {
public void close() throws IOException {
close0();
}
});
}
/**
* Returns the FileDescriptor
* object that represents the connection to
* the actual file in the file system being
* used by this FileInputStream.
*
* @return the file descriptor object associated with this stream.
* @exception IOException if an I/O error occurs.
* @see java.io.FileDescriptor
*/
public final FileDescriptor getFD() throws IOException {
if (fd != null) {
return fd;
}
throw new IOException();
}
/**
* Returns the unique {@link java.nio.channels.FileChannel FileChannel}
* object associated with this file input stream.
*
*
The initial {@link java.nio.channels.FileChannel#position()
* position} of the returned channel will be equal to the
* number of bytes read from the file so far. Reading bytes from this
* stream will increment the channel's position. Changing the channel's
* position, either explicitly or by reading, will change this stream's
* file position.
*
* @return the file channel associated with this file input stream
*
* @since 1.4
* @spec JSR-51
*/
public FileChannel getChannel() {
synchronized (this) {
if (channel == null) {
channel = FileChannelImpl.open(fd, path, true, false, this);
}
return channel;
}
}
private static native void initIDs();
private native void close0() throws IOException;
static {
initIDs();
}
/**
* Ensures that the close method of this file input stream is
* called when there are no more references to it.
*
* @exception IOException if an I/O error occurs.
* @see java.io.FileInputStream#close()
*/
protected void finalize() throws IOException {
if ((fd != null) && (fd != FileDescriptor.in)) {
/* if fd is shared, the references in FileDescriptor
* will ensure that finalizer is only called when
* safe to do so. All references using the fd have
* become unreachable. We can call close()
*/
close();
}
}
}
Ref
- https://zhuanlan.zhihu.com/p/27931572