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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