java源码分析04-FileInputStream

蔚落 2022-08-10 03:43 147阅读 0赞

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今天，我们来看下FileInputStream的内部结构

# 1.类结构 #

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public
    class FileInputStream extends InputStream
    {

继承自InputStream抽象类，实现父类的所有抽象方法。

# 2.内部结构 #

构造函数

public FileInputStream(String name) throws FileNotFoundException {
            this(name != null ? new File(name) : null);
        }

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.incrementAndGetUseCount();
            this.path = name;
            open(name);
        }

final boolean isInvalid() {
            if (status == null) {
                status = (this.path.indexOf('\u0000') < 0) ? PathStatus.CHECKED
                                                           : PathStatus.INVALID;
            }
            return status == PathStatus.INVALID;
        }

private native void open(String name) throws FileNotFoundException;

构造函数可以传入多种形式，String类型也是转化为File类型。  
  
 此处抛出了文件不存在异常，因此实例化的时候，需要加上try..catch或者在方法上抛出

异常，交给下一个调用者处理。

需要注意的是：第一，文件读取的时候还有权限检查的问题，类似于Linux下的文件访问权限。

第二，路径的合法性也需要判断；第三，先获取文件描述符对象

read方法

* @return     the next byte of data, or <code>-1</code> if the end of the
         *             file is reached.
         * @exception  IOException  if an I/O error occurs.
         */
        public int read() throws IOException {
            Object traceContext = IoTrace.fileReadBegin(path);
            int b = 0;
            try {
                b = read0();
            } finally {
                IoTrace.fileReadEnd(traceContext, b == -1 ? 0 : 1);
            }
            return b;
        }

注意返回值是int类型，-1代表字节流结束，否则代表当前字节。

skip方法

* @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;

available方法

* <p> 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;

信道

/**
         * Returns the unique {@link java.nio.channels.FileChannel FileChannel}
         * object associated with this file input stream.
         *
         * <p> The initial {@link java.nio.channels.FileChannel#position()
         * </code>position<code>} 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);
    
                    /*
                     * Increment fd's use count. Invoking the channel's close()
                     * method will result in decrementing the use count set for
                     * the channel.
                     */
                    fd.incrementAndGetUseCount();
                }
                return channel;
            }
        }

属性

/* File Descriptor - handle to the open file */
        private final FileDescriptor fd;
    
        /* The path of the referenced file (null if the stream is created with a file descriptor) */
        private final String path;
    
        private FileChannel channel = null;
    
        private final Object closeLock = new Object();
        private volatile boolean closed = false;
    
        private static final ThreadLocal<Boolean> runningFinalize =
            new ThreadLocal<>();

文件描述符类的实例用作与基础机器有关的某种结构的不透明句柄，该结构表示开放文件、开放套接字或者字节的另一个源或接收者。文件描述符的主要实际用途是创建一个包含该结构的 `FileInputStream` 或 `FileOutputStream`。

path代表文件所在路径

channel代表NIO中的信道

closeLock代表

closed代表

runningFinalize代表

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