Java-IO之PrintStream（打印输出流）

PrintStream是打印输出流，继承于FilterOutputStream，PrintStream是用来装饰其他输出流，为其他输出流添加功能，方便他们打印出各种数据值表示形式。与其他输出流不同，PrintStream永远不会抛出IOException，它产生的错误会被自身的函数所捕获并设置错误标记，用户可以通过checkError（）返回错误标记，查看是否产生IOException。PrintStream提供了自动flush和字符集设置功能，写入的数据会立刻调用flush（）函数。

PrintStream主要的函数列表：

PrintStream(OutputStream out)
// 将“输出流out”作为PrintStream的输出流，自动flush，并且采用默认字符集。
PrintStream(OutputStream out, boolean autoFlush)
// 将“输出流out”作为PrintStream的输出流，自动flush，采用charsetName字符集。
PrintStream(OutputStream out, boolean autoFlush, String charsetName)
// 创建file对应的FileOutputStream，然后将该FileOutputStream作为PrintStream的输出流，不自动flush，采用默认字符集。
PrintStream(File file)
// 创建file对应的FileOutputStream，然后将该FileOutputStream作为PrintStream的输出流，不自动flush，采用charsetName字符集。
PrintStream(File file, String charsetName)
// 创建fileName对应的FileOutputStream，然后将该FileOutputStream作为PrintStream的输出流，不自动flush，采用默认字符集。
PrintStream(String fileName)
// 创建fileName对应的FileOutputStream，然后将该FileOutputStream作为PrintStream的输出流，不自动flush，采用charsetName字符集。
PrintStream(String fileName, String charsetName)
// 将“字符c”追加到“PrintStream输出流中”
PrintStream     append(char c)
// 将“字符序列从start(包括)到end(不包括)的全部字符”追加到“PrintStream输出流中”
PrintStream     append(CharSequence charSequence, int start, int end)
// 将“字符序列的全部字符”追加到“PrintStream输出流中”
PrintStream     append(CharSequence charSequence)
// flush“PrintStream输出流缓冲中的数据”，并检查错误
boolean     checkError()
// 关闭“PrintStream输出流”
synchronized void     close()
// flush“PrintStream输出流缓冲中的数据”。
// 例如，PrintStream装饰的是FileOutputStream，则调用flush时会将数据写入到文件中
synchronized void     flush()
// 根据“Locale值(区域属性)”来格式化数据
PrintStream     format(Locale l, String format, Object... args)
// 根据“默认的Locale值(区域属性)”来格式化数据
PrintStream     format(String format, Object... args)
// 将“float数据f对应的字符串”写入到“PrintStream输出流”中，print实际调用的是write函数
void     print(float f)
// 将“double数据d对应的字符串”写入到“PrintStream输出流”中，print实际调用的是write函数
void     print(double d)
// 将“字符串数据str”写入到“PrintStream输出流”中，print实际调用的是write函数
synchronized void     print(String str)
// 将“对象o对应的字符串”写入到“PrintStream输出流”中，print实际调用的是write函数
void     print(Object o)
// 将“字符c对应的字符串”写入到“PrintStream输出流”中，print实际调用的是write函数
void     print(char c)
// 将“字符数组chars对应的字符串”写入到“PrintStream输出流”中，print实际调用的是write函数
void     print(char[] chars)
// 将“long型数据l对应的字符串”写入到“PrintStream输出流”中，print实际调用的是write函数
void     print(long l)
// 将“int数据i对应的字符串”写入到“PrintStream输出流”中，print实际调用的是write函数
void     print(int i)
// 将“boolean数据b对应的字符串”写入到“PrintStream输出流”中，print实际调用的是write函数
void     print(boolean b)
// 将“数据args”根据“Locale值(区域属性)”按照format格式化，并写入到“PrintStream输出流”中
PrintStream     printf(Locale l, String format, Object... args)
// 将“数据args”根据“默认Locale值(区域属性)”按照format格式化，并写入到“PrintStream输出流”中
PrintStream     printf(String format, Object... args)
// 将“换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println()
// 将“float数据对应的字符串+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println(float f)
// 将“int数据对应的字符串+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println(int i)
// 将“long数据对应的字符串+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println(long l)
// 将“对象o对应的字符串+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println(Object o)
// 将“字符数组chars对应的字符串+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println(char[] chars)
// 将“字符串str+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
synchronized void     println(String str)
// 将“字符c对应的字符串+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println(char c)
// 将“double数据对应的字符串+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println(double d)
// 将“boolean数据对应的字符串+换行符”写入到“PrintStream输出流”中，println实际调用的是write函数
void     println(boolean b)
// 将数据oneByte写入到“PrintStream输出流”中。oneByte虽然是int类型，但实际只会写入一个字节
synchronized void     write(int oneByte)
// 将“buffer中从offset开始的length个字节”写入到“PrintStream输出流”中。
void     write(byte[] buffer, int offset, int length)
示例程序：
public class PrintStreamTest {

    public static void main(String[] args) {
        testPrintStreamConstrutor1() ;
        // 测试write(), print(), println(), printf()等接口。
        testPrintStreamAPIS() ;
    }
    private static void testPrintStreamConstrutor1() {
        // 0x61对应ASCII码的字母'a'，0x62对应ASCII码的字母'b', ...
        final byte[] arr={0x61, 0x62, 0x63, 0x64, 0x65 }; // abced
        try {
            // 创建文件“file.txt”的File对象
            File file = new File("file1.txt");
            // 创建文件对应FileOutputStream
            PrintStream out = new PrintStream(new FileOutputStream(file));
            // 将“字节数组arr”全部写入到输出流中
            out.write(arr);
            // 关闭输出流
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /**
     * 测试write(), print(), println(), printf()等接口。
    */
    private static void testPrintStreamAPIS() {
        // 0x61对应ASCII码的字母'a'，0x62对应ASCII码的字母'b', ...
        final byte[] arr={0x61, 0x62, 0x63, 0x64, 0x65 }; // abced
        try {
            // 创建文件对应FileOutputStream
            PrintStream out = new PrintStream("other.txt");

            // 将字符串“hello PrintStream”+回车符，写入到输出流中
            out.println("hello PrintStream");
            // 将0x41写入到输出流中
            // 0x41对应ASCII码的字母'A'，也就是写入字符'A'
            out.write(0x41);
            // 将字符串"65"写入到输出流中。
            // out.print(0x41); 等价于 out.write(String.valueOf(0x41));
            out.print(0x41);
            // 将字符'B'追加到输出流中
            out.append('B');

            // 将"CDE is 5" + 回车  写入到输出流中
            String str = "CDE";
            int num = 5;
            out.printf("%s is %d\n", str, num);

            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

file1.txt文件中为: abcde

other.txt文件中为:

hello PrintStream

A65BCDE is 5

基于JDK8的PrintStream的源码：

is.charOut = new OutputStreamWriter(this);
        this.textOut = new BufferedWriter(charOut);
    }
    //out输出流，自动autoFlash，charset字符集
    private PrintStream(boolean autoFlush, OutputStream out, Charset charset) {
        super(out);
        this.autoFlush = autoFlush;
        this.charOut = new OutputStreamWriter(this, charset);
        this.textOut = new BufferedWriter(charOut);
    }

    /* Variant of the private constructor so that the given charset name
     * can be verified before evaluating the OutputStream argument. Used
     * by constructors creating a FileOutputStream that also take a
     * charset name.
     */
    private PrintStream(boolean autoFlush, Charset charset, OutputStream out) throws UnsupportedEncodingException
    {
        this(autoFlush, out, charset);
    }
    //out输出流，不会自动flush，m默认字符集
    public PrintStream(OutputStream out) {
        this(out, false);
    }
    public PrintStream(OutputStream out, boolean autoFlush) {
        this(autoFlush, requireNonNull(out, "Null output stream"));
    }

    public PrintStream(OutputStream out, boolean autoFlush, String encoding) throws UnsupportedEncodingException
    {
        this(autoFlush,
        requireNonNull(out, "Null output stream"),
        toCharset(encoding));
    }
    //将FileOutputStream作为输入流，不自动flush，默认字符集
    public PrintStream(String fileName) throws FileNotFoundException {
        this(false, new FileOutputStream(fileName));
    }
    //FileOutputStream输出流，不自动flush，csn字符集
    public PrintStream(String fileName, String csn)throws FileNotFoundException, UnsupportedEncodingException
    {
        // ensure charset is checked before the file is opened
        this(false, toCharset(csn), new FileOutputStream(fileName));
    }
    //FileOutputStream输出流，不自动flush，默认字符集
    public PrintStream(File file) throws FileNotFoundException {
        this(false, new FileOutputStream(file));
    }
    //FileOutputStream输出流，csn字符集，不自动flush
    public PrintStream(File file, String csn)throws FileNotFoundException, UnsupportedEncodingException
    {
        // ensure charset is checked before the file is opened
        this(false, toCharset(csn), new FileOutputStream(file));
    }

    /** Check to make sure that the stream has not been closed */
    //输出流不为空
    private void ensureOpen() throws IOException {
        if (out == null)
            throw new IOException("Stream closed");
    }
    //刷新
    public void flush() {
        synchronized (this) {
            try {
                ensureOpen();
                out.flush();
            }
            catch (IOException x) {
                trouble = true;
            }
        }
    }

    private boolean closing = false; /* To avoid recursive closing */
    //关闭输出流
    public void close() {
        synchronized (this) {
            if (! closing) {
                closing = true;
                try {
                    textOut.close();
                    out.close();
                }
                catch (IOException x) {
                    trouble = true;
                }
                textOut = null;
                charOut = null;
                out = null;
            }
        }
    }
    //flush PrintStream输出流缓冲中数据，并检查错误
    public boolean checkError() {
        if (out != null)
            flush();
        if (out instanceof java.io.PrintStream) {
            PrintStream ps = (PrintStream) out;
            return ps.checkError();
        }
        return trouble;
    }
    //出现错误
    protected void setError() {
        trouble = true;
    }

    //清空内部错误
    protected void clearError() {
        trouble = false;
    }

    /*
     * Exception-catching, synchronized output operations,
     * which also implement the write() methods of OutputStream
     */

    //将数据b写入到PrintStream中，b虽然是int类型，但实际只会写入一个字节
    public void write(int b) {
        try {
            synchronized (this) {
                ensureOpen();
                out.write(b);
                if ((b == '\n') && autoFlush)
                    out.flush();
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }

    public void write(byte buf[], int off, int len) {
        try {
            synchronized (this) {
                ensureOpen();
                out.write(buf, off, len);
                if (autoFlush)
                    out.flush();
             }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }

    /*
     * The following private methods on the text- and character-output streams
     * always flush the stream buffers, so that writes to the underlying byte
     * stream occur as promptly as with the original PrintStream.
     */
    //将b中的全部数据写入到PrintStream中
    private void write(char buf[]) {
        try {
            synchronized (this) {
                ensureOpen();
                textOut.write(buf);
                textOut.flushBuffer();
                charOut.flushBuffer();
                if (autoFlush) {
                    for (int i = 0; i < buf.length; i++)
                        if (buf[i] == '\n')
                            out.flush();
                 }
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }
    //String写到PrintStream中
    private void write(String s) {
        try {
            synchronized (this) {
                ensureOpen();
                textOut.write(s);
                textOut.flushBuffer();
                charOut.flushBuffer();
                if (autoFlush && (s.indexOf('\n') >= 0))
                    out.flush();
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }
    //换行符写到PrintStream中
    private void newLine() {
        try {
            synchronized (this) {
                ensureOpen();
                textOut.newLine();
                textOut.flushBuffer();
                charOut.flushBuffer();
                if (autoFlush)
                    out.flush();
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }

    /* Methods that do not terminate lines */

    //将b对应的字符串写到PrintStream中
    public void print(boolean b) {
        write(b ? "true" : "false");
    }

    //最后都是转化为String

    //字符串
    public void print(char c) {
        write(String.valueOf(c));
    }
    //int类型
    public void print(int i) {
        write(String.valueOf(i));
    }
    //long类型
    public void print(long l) {
        write(String.valueOf(l));
    }
    //float
    public void print(float f) {
        write(String.valueOf(f));
    }
    //double
    public void print(double d) {
        write(String.valueOf(d));
    }
    //字符数组
    public void print(char s[]) {
        write(s);
    }
    //字符串
    public void print(String s) {
        if (s == null) {
            s = "null";
        }
        write(s);
   }
    //对象
    public void print(Object obj) {
        write(String.valueOf(obj));
    }

    /* Methods that do terminate lines */
    //换行
    public void println() {
        newLine();
    }
    //boolean+换行
    public void println(boolean x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }
    //char+换行
    public void println(char x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }
    //int+换行
    public void println(int x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }
    //long+换行
    public void println(long x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }
    //float+换行
    public void println(float x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }
    //double+换行
    public void println(double x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }
    //char数组+换行
    public void println(char x[]) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }
    //字符串+换行
    public void println(String x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }
    //对象+换行
    public void println(Object x) {
        String s = String.valueOf(x);
        synchronized (this) {
            print(s);
            newLine();
        }
    }

    public PrintStream printf(String format, Object ... args) {
            return format(format, args);
    }

    public PrintStream printf(Locale l, String format, Object ... args) {
        return format(l, format, args);
    }
    // 将“数据args”根据“默认Locale值(区域属性)”按照format格式化，并写入到“PrintStream输出流”中
    public PrintStream format(String format, Object ... args) {
        try {
            synchronized (this) {
                ensureOpen();
                if ((formatter == null)
                        || (formatter.locale() != Locale.getDefault()))
                    formatter = new Formatter((Appendable) this);
                    formatter.format(Locale.getDefault(), format, args);
            }
        } catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        } catch (IOException x) {
            trouble = true;
        }
        return this;
    }
    public PrintStream format(Locale l, String format, Object ... args) {
        try {
            synchronized (this) {
                ensureOpen();
                if ((formatter == null)
                        || (formatter.locale() != l))
                    formatter = new Formatter(this, l);
                    formatter.format(l, format, args);
            }
        } catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        } catch (IOException x) {
        trouble = true;
        }
        return this;
    }

    public PrintStream append(CharSequence csq) {
        if (csq == null)
            print("null");
        else
            print(csq.toString());
        return this;
    }
    public PrintStream append(CharSequence csq, int start, int end) {
        CharSequence cs = (csq == null ? "null" : csq);
        write(cs.subSequence(start, end).toString());
        return this;
    }
    public PrintStream append(char c) {
        print(c);
        return this;
    }

}