分析FileInputStream，其中finalize()被覆写，优先使用finalize(),close()方法可能内存泄漏，或者手动colse()之前做好检查
package java.io;
import java.nio.channels.FileChannel;
import sun.nio.ch.FileChannelImpl;
/**
* A <code>FileInputStream</code> obtains input bytes
* from a file in a file system. What files
* are available depends on the host environment.
*
* <p><code>FileInputStream</code> is meant for reading streams of raw bytes
* such as image data. For reading streams of characters, consider using
* <code>FileReader</code>.
*
* @author Arthur van Hoff
* @see java.io.File
* @see java.io.FileDescriptor
* @see java.io.FileOutputStream
* @see java.nio.file.Files#newInputStream
* @since JDK1.0
*/
public
class FileInputStream extends InputStream
{
/* File Descriptor - handle to the open file */
private final FileDescriptor fd;
/**
* 文件路径
*（如果传入FileDescriptor实例化输入流则其为null）
*/
private final String path;
/**
* 读、写、操作文件的通道
*/
private FileChannel channel = null;
/**
* 锁，给close()加锁
*/
private final Object closeLock = new Object();
/**
* 锁的条件值
*/
private volatile boolean closed = false;
/**
* 检查name是否为null，不是调用另外一个构造函数，传入 new File(name)
* @param name
* @throws FileNotFoundException
*/
public FileInputStream(String name) throws FileNotFoundException {
this(name != null ? new File(name) : null);
}
/**
* 1、为name赋值
* 2、安全检查
* 3、判断文件是否存在
* 4、创建一个文件描述类
* 5、绑定其到this
* 6、打开文件（native方法）
* @param file
* @throws FileNotFoundException
*/
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);
}
/**
* 不推荐采用该构造方法
* 引用自jdk：文件描述符类的实例用作表示打开文件，开放套接字或其他字节源或信宿的底层机器特定结构的不透明句柄。 文件描述符的主要实际用途是创建一个FileInputStream或FileOutputStream来包含它。 应用程序不应创建自己的文件描述符。
* @param fdObj
*/
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);
}
/**
* native方法，打开文件
* @param name
* @throws FileNotFoundException
*/
private native void open0(String name) throws FileNotFoundException;
/**
* 打开文件
* @param name
* @throws FileNotFoundException
*/
private void open(String name) throws FileNotFoundException {
open0(name);
}
/**
* 读取字节
* @return
* @throws IOException
*/
public int read() throws IOException {
return read0();
}
/**
* native方法、读取字节
* @return
* @throws IOException
*/
private native int read0() throws IOException;
/**
* native方法，读取字节数组
* @param b
* @param off
* @param len
* @return
* @throws IOException
*/
private native int readBytes(byte b[], int off, int len) throws IOException;
/**
* 读取字节数组
* @param b
* @return
* @throws IOException
*/
public int read(byte b[]) throws IOException {
return readBytes(b, 0, b.length);
}
/**
* 读取字节
* @param b
* @param off
* @param len
* @return
* @throws IOException
*/
public int read(byte b[], int off, int len) throws IOException {
return readBytes(b, off, len);
}
/**
* 跳过n个字节
* @param n
* @return
* @throws IOException
*/
public long skip(long n) throws IOException {
return skip0(n);
}
private native long skip0(long n) throws IOException;
/**
* 可读取最大字节数
* @return
* @throws IOException
*/
public int available() throws IOException {
return available0();
}
private native int available0() throws IOException;
/**
* 关闭输入流
* @throws IOException
*/
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();
}
});
}
/**
* 获取文件描述类
* @return
* @throws IOException
*/
public final FileDescriptor getFD() throws IOException {
if (fd != null) {
return fd;
}
throw new IOException();
}
/**
* 获取文件描述通道
* @return
*/
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();
}
/**
*确保输入流不持有其他对象的引用，再关闭输入流
* @throws IOException
*/
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();
}
}
}
分析FileOutputStream，和FileInputStream类似，多了一个append属性，表示追加和覆写两种模式
package java.io;
import java.nio.channels.FileChannel;
import sun.nio.ch.FileChannelImpl;
/**
* A file output stream is an output stream for writing data to a
* <code>File</code> or to a <code>FileDescriptor</code>. Whether or not
* a file is available or may be created depends upon the underlying
* platform. Some platforms, in particular, allow a file to be opened
* for writing by only one <tt>FileOutputStream</tt> (or other
* file-writing object) at a time. In such situations the constructors in
* this class will fail if the file involved is already open.
*
* <p><code>FileOutputStream</code> is meant for writing streams of raw bytes
* such as image data. For writing streams of characters, consider using
* <code>FileWriter</code>.
*
* @author Arthur van Hoff
* @see java.io.File
* @see java.io.FileDescriptor
* @see java.io.FileInputStream
* @see java.nio.file.Files#newOutputStream
* @since JDK1.0
*/
public
class FileOutputStream extends OutputStream
{
/**
* The system dependent file descriptor.
*/
private final FileDescriptor fd;
/**
* True if the file is opened for append.
*/
private final boolean append;
/**
* The associated channel, initialized lazily.
*/
private FileChannel channel;
/**
* The path of the referenced file
* (null if the stream is created with a file descriptor)
*/
private final String path;
private final Object closeLock = new Object();
private volatile boolean closed = false;
/**
* Creates a file output stream to write to the file with the
* specified name. A new <code>FileDescriptor</code> object is
* created to represent this file connection.
* <p>
* First, if there is a security manager, its <code>checkWrite</code>
* method is called with <code>name</code> as its argument.
* <p>
* If the file exists but is a directory rather than a regular file, does
* not exist but cannot be created, or cannot be opened for any other
* reason then a <code>FileNotFoundException</code> is thrown.
*
* @param name the system-dependent filename
* @exception FileNotFoundException if the file exists but is a directory
* rather than a regular file, does not exist but cannot
* be created, or cannot be opened for any other reason
* @exception SecurityException if a security manager exists and its
* <code>checkWrite</code> method denies write access
* to the file.
* @see java.lang.SecurityManager#checkWrite(java.lang.String)
*/
public FileOutputStream(String name) throws FileNotFoundException {
this(name != null ? new File(name) : null, false);
}
/**
* Creates a file output stream to write to the file with the specified
* name. If the second argument is <code>true</code>, then
* bytes will be written to the end of the file rather than the beginning.
* A new <code>FileDescriptor</code> object is created to represent this
* file connection.
* <p>
* First, if there is a security manager, its <code>checkWrite</code>
* method is called with <code>name</code> as its argument.
* <p>
* If the file exists but is a directory rather than a regular file, does
* not exist but cannot be created, or cannot be opened for any other
* reason then a <code>FileNotFoundException</code> is thrown.
*
* @param name the system-dependent file name
* @param append if <code>true</code>, then bytes will be written
* to the end of the file rather than the beginning
* @exception FileNotFoundException if the file exists but is a directory
* rather than a regular file, does not exist but cannot
* be created, or cannot be opened for any other reason.
* @exception SecurityException if a security manager exists and its
* <code>checkWrite</code> method denies write access
* to the file.
* @see java.lang.SecurityManager#checkWrite(java.lang.String)
* @since JDK1.1
*/
public FileOutputStream(String name, boolean append)
throws FileNotFoundException
{
this(name != null ? new File(name) : null, append);
}
/**
* Creates a file output stream to write to the file represented by
* the specified <code>File</code> object. A new
* <code>FileDescriptor</code> object is created to represent this
* file connection.
* <p>
* First, if there is a security manager, its <code>checkWrite</code>
* method is called with the path represented by the <code>file</code>
* argument as its argument.
* <p>
* If the file exists but is a directory rather than a regular file, does
* not exist but cannot be created, or cannot be opened for any other
* reason then a <code>FileNotFoundException</code> is thrown.
*
* @param file the file to be opened for writing.
* @exception FileNotFoundException if the file exists but is a directory
* rather than a regular file, does not exist but cannot
* be created, or cannot be opened for any other reason
* @exception SecurityException if a security manager exists and its
* <code>checkWrite</code> method denies write access
* to the file.
* @see java.io.File#getPath()
* @see java.lang.SecurityException
* @see java.lang.SecurityManager#checkWrite(java.lang.String)
*/
public FileOutputStream(File file) throws FileNotFoundException {
this(file, false);
}
/**
* Creates a file output stream to write to the file represented by
* the specified <code>File</code> object. If the second argument is
* <code>true</code>, then bytes will be written to the end of the file
* rather than the beginning. A new <code>FileDescriptor</code> object is
* created to represent this file connection.
* <p>
* First, if there is a security manager, its <code>checkWrite</code>
* method is called with the path represented by the <code>file</code>
* argument as its argument.
* <p>
* If the file exists but is a directory rather than a regular file, does
* not exist but cannot be created, or cannot be opened for any other
* reason then a <code>FileNotFoundException</code> is thrown.
*
* @param file the file to be opened for writing.
* @param append if <code>true</code>, then bytes will be written
* to the end of the file rather than the beginning
* @exception FileNotFoundException if the file exists but is a directory
* rather than a regular file, does not exist but cannot
* be created, or cannot be opened for any other reason
* @exception SecurityException if a security manager exists and its
* <code>checkWrite</code> method denies write access
* to the file.
* @see java.io.File#getPath()
* @see java.lang.SecurityException
* @see java.lang.SecurityManager#checkWrite(java.lang.String)
* @since 1.4
*/
public FileOutputStream(File file, boolean append)
throws FileNotFoundException
{
String name = (file != null ? file.getPath() : null);
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkWrite(name);
}
if (name == null) {
throw new NullPointerException();
}
if (file.isInvalid()) {
throw new FileNotFoundException("Invalid file path");
}
this.fd = new FileDescriptor();
fd.attach(this);
this.append = append;
this.path = name;
open(name, append);
}
/**
* Creates a file output stream to write to the specified file
* descriptor, which represents an existing connection to an actual
* file in the file system.
* <p>
* First, if there is a security manager, its <code>checkWrite</code>
* method is called with the file descriptor <code>fdObj</code>
* argument as its argument.
* <p>
* If <code>fdObj</code> is null then a <code>NullPointerException</code>
* is thrown.
* <p>
* This constructor does not throw an exception if <code>fdObj</code>
* 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 <code>IOException</code> is thrown.
*
* @param fdObj the file descriptor to be opened for writing
* @exception SecurityException if a security manager exists and its
* <code>checkWrite</code> method denies
* write access to the file descriptor
* @see java.lang.SecurityManager#checkWrite(java.io.FileDescriptor)
*/
public FileOutputStream(FileDescriptor fdObj) {
SecurityManager security = System.getSecurityManager();
if (fdObj == null) {
throw new NullPointerException();
}
if (security != null) {
security.checkWrite(fdObj);
}
this.fd = fdObj;
this.append = false;
this.path = null;
fd.attach(this);
}
/**
* Opens a file, with the specified name, for overwriting or appending.
* @param name name of file to be opened
* @param append whether the file is to be opened in append mode
*/
private native void open0(String name, boolean append)
throws FileNotFoundException;
// wrap native call to allow instrumentation
/**
* Opens a file, with the specified name, for overwriting or appending.
* @param name name of file to be opened
* @param append whether the file is to be opened in append mode
*/
private void open(String name, boolean append)
throws FileNotFoundException {
open0(name, append);
}
/**
* Writes the specified byte to this file output stream.
*
* @param b the byte to be written.
* @param append {@code true} if the write operation first
* advances the position to the end of file
*/
private native void write(int b, boolean append) throws IOException;
/**
* Writes the specified byte to this file output stream. Implements
* the <code>write</code> method of <code>OutputStream</code>.
*
* @param b the byte to be written.
* @exception IOException if an I/O error occurs.
*/
public void write(int b) throws IOException {
write(b, append);
}
/**
* Writes a sub array 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
* @param append {@code true} to first advance the position to the
* end of file
* @exception IOException If an I/O error has occurred.
*/
private native void writeBytes(byte b[], int off, int len, boolean append)
throws IOException;
/**
* Writes <code>b.length</code> bytes from the specified byte array
* to this file output stream.
*
* @param b the data.
* @exception IOException if an I/O error occurs.
*/
public void write(byte b[]) throws IOException {
writeBytes(b, 0, b.length, append);
}
/**
* Writes <code>len</code> bytes from the specified byte array
* starting at offset <code>off</code> to this file output stream.
*
* @param b the data.
* @param off the start offset in the data.
* @param len the number of bytes to write.
* @exception IOException if an I/O error occurs.
*/
public void write(byte b[], int off, int len) throws IOException {
writeBytes(b, off, len, append);
}
/**
* Closes this file output stream and releases any system resources
* associated with this stream. This file output stream may no longer
* be used for writing bytes.
*
* <p> 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 file descriptor associated with this stream.
*
* @return the <code>FileDescriptor</code> object that represents
* the connection to the file in the file system being used
* by this <code>FileOutputStream</code> object.
*
* @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 output stream.
*
* <p> The initial {@link java.nio.channels.FileChannel#position()
* position} of the returned channel will be equal to the
* number of bytes written to the file so far unless this stream is in
* append mode, in which case it will be equal to the size of the file.
* Writing bytes to this stream will increment the channel's position
* accordingly. Changing the channel's position, either explicitly or by
* writing, will change this stream's file position.
*
* @return the file channel associated with this file output stream
*
* @since 1.4
* @spec JSR-51
*/
public FileChannel getChannel() {
synchronized (this) {
if (channel == null) {
channel = FileChannelImpl.open(fd, path, false, true, append, this);
}
return channel;
}
}
/**
* Cleans up the connection to the file, and ensures that the
* <code>close</code> method of this file output stream is
* called when there are no more references to this stream.
*
* @exception IOException if an I/O error occurs.
* @see java.io.FileInputStream#close()
*/
protected void finalize() throws IOException {
if (fd != null) {
if (fd == FileDescriptor.out || fd == FileDescriptor.err) {
flush();
} else {
/* 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();
}
}
}
private native void close0() throws IOException;
private static native void initIDs();
static {
initIDs();
}
}