廖雪峰Java6 IO编程-3Reader和Writer-2Writer

1.java.io.Writer和java.io.OutputStream的区别

OutputStream	Writer
字节流，以byte为单位	字符流，以char为单位
写入字节（0-255）：void write(int b)	写入字符（0-65535）：void write(int c)
写入字节数组 void write(byte[] b)	写入字符数组void wirlte(char[] c)
void write(byte[] b, int off, int len)	void write(char[] c, int off, int len)
	可以直接写入字符串wirte(String s)

2.Writer

java.io.Writer是所有字符输出流的超类：

• void write(int c)：写入一个字符（0-65535）
  * write方法也是阻塞的。必须等待write方法返回才能执行下一行代码
  * FileWriter可以从文件获取Writer，字符编码是系统默认的UTF-8。修改编码格式参见2.3

    Writer writer = new FileWriter("test.txt");

• void write(char[] c)：写入字符数组的所有字符
• void write(char[] c, int off, int len)：写入字符数组指定范围的字符
• void write(String s)：写入String表示的所有字符
• void close()：关闭Writer流

2.1Writer写入单个字符：

static void writeFile1(String file) throws IOException{
        //手动关闭
        Writer writer = new FileWriter(file);
        writer.write(65);
        writer.close();
    }
    static void writeFile2(String file) throws IOException{
        //try..finall关闭Writer流
        Writer writer = null;
        try{
            writer = new FileWriter(file);
            writer.write(66);
        }finally {
            writer.close();
        }
    }
    static void writeFile3(String file) throws IOException{
        //使用try(resource)自动关闭Writer流
        try(Writer writer = new FileWriter(file)){
            writer.write(67);
        }
    }

2.2Writer一次写入多个字符或字符串

    static void writeFile4(String file) throws IOException{
        try(Writer writer = new FileWriter(file)){
            writer.write("Hello ".toCharArray());//写入char数组
            writer.write("world");//写入字符串
        }
    }

2.3Writer实际上是基于OutputStream构造的：

• FileWriter内部持有一个FileOutputStream
• Writer可以通过OutputStream构造

    OutputStream output = new FileOutputStream(filename);
    Writer writer = new OutputStreamWriter(output, "UTF-8");//使用OutputStream写入byte

    public static void main(String[] args) throws IOException,ClassNotFoundException {
        String file = "./src/main/java/com/testList/output.txt";
        try(Writer writer = new OutputStreamWriter(
                new FileOutputStream(file),"utf-8")) {
            writer.write("Hello ");
            writer.write("你好");
        }
    }

2.4CharArrayWriter可以在内存中模拟一个Writer

    public static void main(String[] args) throws IOException,ClassNotFoundException {
        try(CharArrayWriter writer = new CharArrayWriter()){
            writer.write(65);
            writer.write(66);
            writer.write(67);
            char[] data = writer.toCharArray();
            System.out.println(data);
        }
    }

3.总结

• Writer定义了所有字符输出流的超类
• FileWriter实现了文件字符流输出
• CharArrayWriter在内存中模拟一个字符流输出
• Writer是基于OutputStream构造的：
  * FileWriter使用系统默认编码，无法指定编码
  * 可以通过OutputStreamWriter指定编码
• 使用try(resource)保证Writer正确关闭