java基础---->java输入输出流

　　今天我们总结一下java中关于输入流和输出流的知识，博客的代码选自Thinking in java一书。我突然很想忘了你，就像从未遇见你。

java中的输入流

huhx.txt文件的内容如下： I love you, ch. 中文

一、缓冲中输入文件

public class BufferedInputFile {
    public static String read(String filename) {
        BufferedReader reader = null;
        StringBuilder builder = new StringBuilder();
        try {
            reader = new BufferedReader(new FileReader(filename));
            String line;
            while ((line = reader.readLine()) != null) {
                builder.append(line + "\n");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                reader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return builder.toString();
    }

    public static void main(String[] args) {
        String content = read("file/huhx.txt");
        System.out.println(content);
    }
}

二、从内存输入

public class MemoryInput {
    public static void main(String[] args) {
        StringReader reader = new StringReader(BufferedInputFile.read("file/huhx.txt"));
        int c;
        try {
            while ((c = reader.read()) != -1) {
                System.out.print((char) c);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

三、格式化的内存输入

public class FormattedMemoryInput {
    public static void main(String[] args) {
        DataInputStream inputStream = new DataInputStream(
                new ByteArrayInputStream(BufferedInputFile.read("file/huhx.txt").getBytes()));
        try {
            while (inputStream.available() != 0) {
                System.out.print((char)inputStream.readByte());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

available()的工作方式会随着所读取的媒介类型的不同而有所不同。也就是说在没有阻塞的情况下所能读取的字节数。对于文件，这意味着整个文件。但是对于不同类型的流，可能就不是这样的。

java中输出流

一、基本的文件输出

public class BasicFileOutput {
    static String file = "file/linux.txt";
    public static void main(String[] args) {
        BufferedReader reader = new BufferedReader(new StringReader(BufferedInputFile.read("file/huhx.txt")));
        PrintWriter out = null;
        try {
            out = new PrintWriter(new BufferedWriter(new FileWriter(file)));
            String line;
            while ((line = reader.readLine()) != null) {
                out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            out.close();
        }
        System.out.println(BufferedInputFile.read(file));
    }
}

二、文本文件输出的快捷方式

public class FileOutputShortcut {
    static String file = "file/linux.out"; // 这个也和上述不一样
    public static void main(String[] args) {
        BufferedReader reader = new BufferedReader(new StringReader(BufferedInputFile.read("file/huhx.txt")));
        PrintWriter out = null;
        try {
            out = new PrintWriter(new FileWriter(file)); // 这里和上述不一样
            String line;
            while ((line = reader.readLine()) != null) {
                out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            out.close();
        }
        System.out.println(BufferedInputFile.read(file));
    }
}

三、存储和恢复数据

public class StoringAndRecoveringData {
    public static void main(String[] args) {
        try {
            DataOutputStream out = new DataOutputStream(
                    new BufferedOutputStream(new FileOutputStream("file/chenhui.txt")));
            out.writeDouble(3.1415926);
            out.writeUTF("中文可以吗？");
            out.writeInt(123);
            out.close();

            DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream("file/chenhui.txt")));
            System.out.println(in.readDouble()); // 如果这里是readInt()，会导致后面的readUTF方法报错
            System.out.println(in.readUTF());
            System.out.println(in.readInt());
            in.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

三、读写随机访问文件

public class UsingRandomAccessFile {
    static String file = "file/huhx.txt";

    static void display() throws Exception {
        RandomAccessFile rf = new RandomAccessFile(file, "r");
        System.out.println(rf.readDouble());
        System.out.println(rf.readDouble());
        System.out.println(rf.readUTF());
        rf.close();
    }

    public static void main(String[] args) {
        RandomAccessFile rf;
        try {
            rf = new RandomAccessFile(file, "rw");
            rf.writeDouble(23.654);
            rf.writeDouble(3.14156);
            rf.writeUTF("我爱你！");
            rf.close();
            display();

            rf = new RandomAccessFile(file, "rw");
            rf.seek(1 * 8);
            rf.writeDouble(2.366);
            rf.close();
            display();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
/*
23.654
3.14156
我爱你！
23.654
2.366
我爱你！
*/

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