Java IO体系之Writer

本是古典何须时尚 2022-03-06 02:12 198阅读 0赞

## 介绍 ##

>  *  字符输出流

程序  ----（输出）---->>>  文件

## 源码 ##

package java.io;
    
    
    /** * Abstract class for writing to character streams. * @since JDK1.1 */
    
    public abstract class Writer implements Appendable, Closeable, Flushable { 
    
        private char[] writeBuffer;
        private final int writeBufferSize = 1024;
        protected Object lock;
    
        protected Writer() { 
            this.lock = this;
        }
    
        protected Writer(Object lock) { 
            if (lock == null) { 
                throw new NullPointerException();
            }
            this.lock = lock;
        }
    
        public void write(int c) throws IOException { 
            // synchronized 悲观锁
            synchronized (lock) { 
                if (writeBuffer == null){ 
                    writeBuffer = new char[writeBufferSize];
                }
                writeBuffer[0] = (char) c;
                write(writeBuffer, 0, 1);
            }
        }
    
        public void write(char cbuf[]) throws IOException { 
            write(cbuf, 0, cbuf.length);
        }
    
        abstract public void write(char cbuf[], int off, int len) throws IOException;
    
        public void write(String str) throws IOException { 
            write(str, 0, str.length());
        }
    
        public void write(String str, int off, int len) throws IOException { 
            // synchronized 悲观锁
            synchronized (lock) { 
                char cbuf[];
                if (len <= writeBufferSize) { 
                    if (writeBuffer == null) { 
                        writeBuffer = new char[writeBufferSize];
                    }
                    cbuf = writeBuffer;
                } else {     // Don't permanently allocate very large buffers.
                    cbuf = new char[len];
                }
                str.getChars(off, (off + len), cbuf, 0);
                write(cbuf, 0, len);
            }
        }
    
        public Writer append(CharSequence csq) throws IOException { 
            if (csq == null)
                write("null");
            else
                write(csq.toString());
            return this;
        }
    
        /** * Appends a subsequence of the specified character sequence to this writer. * <tt>Appendable</tt>. * * @since 1.5 */
        public Writer append(CharSequence csq, int start, int end) throws IOException { 
            CharSequence cs = (csq == null ? "null" : csq);
            write(cs.subSequence(start, end).toString());
            return this;
        }
    
        /** * Appends the specified character to this writer. * @since 1.5 */
        public Writer append(char c) throws IOException { 
            write(c);
            return this;
        }
    
        /** * Flushes the stream. */
        abstract public void flush() throws IOException;
    
        abstract public void close() throws IOException;
    
    }