Java基础Demo -- IO 语法器示例

PushbackInputStream 语法器的运用
/**
* 语法解析器：PushbackInputStream
* 举例1：解析语句"for(int i=0;i<10;i++)"中的for关键字,扫描到"for"是不是就可以说是个关键字了呢？不行，说不定后面是“for1”，那就是个变量而不是关键字了，知道看到“(”才恍然大悟，哦，我可以安全地说“看到for关键字”了，但“(”还得归还给输入流，因为需要后面继续扫描。
* 举例2：解析HTML文档的时候，我需要根据它的“meta”标签的“charset”属性来决定使用哪种字符集进行解析，但HTML可不是“charset”而是“<html>”开头的哦！所以需要通过PushbackInputStream缓冲前面一段内容，等取到字符集名称后在把读到的流全部归还，再用指定的字符集进行解析。
* 举例3：解析文件内容中的英文字母还是中文汉字。
*/

import java.io.*;

public class PushbackInputStreamDemo 
{
	public static void main(String[] args) 
	{
		System.out.println("\r\n示例1：PushbackInputStream.read()单字节解析器");

		String str = "if (a == 4) a = 0 ;";
		byte[] bArray = str.getBytes();
		ByteArrayInputStream in = new ByteArrayInputStream(bArray);

		try(PushbackInputStream pin = new PushbackInputStream(in)){
			int c;
			while( (c=pin.read()) !=-1 ){
				switch(c){
					case '=':
						if( (c=pin.read()) == '=' ){
							System.out.print(".equals.");
						}else{
							System.out.print("->");
							pin.unread(c);
						}
						break;
					default:
						System.out.print((char)c);
						break;
				}
			}
			System.out.println();

		}catch(Exception e){}

		System.out.println("\r\n示例2：PushbackInputStream.read(array[2])双字节解析器");

		String str2 = "if (a == 4) a = 0 ;";
		byte[] bArray2 = str2.getBytes();
		ByteArrayInputStream in2 = new ByteArrayInputStream(bArray2);

		try(PushbackInputStream pin2 = new PushbackInputStream(in2)){
			int count;
			byte[] array = new byte[2];			
			while( pin2.available()>1 && (count=pin2.read(array)) !=-1 ){
				if( (new String(array)).equals("==") ){
					System.out.print(".equals.");
				}
				else if( (new String(array)).equals("= ") ){
					System.out.print("->");
					pin2.unread(array[1]);
				}
				else{
					String ss;
					System.out.print(ss = new String(array));
					if(ss.contains("="))
						pin2.unread(array[1]);
				}
			}

			if(pin2.available()>0){
				System.out.println((char)pin2.read());
			}

			System.out.println();

		}catch(Exception e){}

		System.out.println("\r\n示例3：PushbackReader.read()单字符解析器");

		String str3 = "if (a == 4) a = 0 ;";
		char[] cArray3 = new char[str3.length()]; 
		str3.getChars(0,str3.length(),cArray3,0);
		CharArrayReader in3 = new CharArrayReader(cArray3);

		try(PushbackReader pin3 = new PushbackReader(in3)){
			int c;
			while( (c=pin3.read()) !=-1 ){
				switch(c){
					case '=':
						if( (c=pin3.read()) == '=' ){
							System.out.print(".equals.");
						}else{
							System.out.print("->");
							pin3.unread(c);
						}
						break;
					default:
						System.out.print((char)c);
						break;
				}
			}

			System.out.println();

		}catch(Exception e){}

		System.out.println("\r\n示例4：PushbackInputStream.read(array[2])双字节解析器：解析英文和中文");

		String str0 = "a我b是c学d生;";
		byte[] bArray0 = str0.getBytes();
		ByteArrayInputStream in0 = new ByteArrayInputStream(bArray0);

		try( PushbackInputStream pin0 = new PushbackInputStream(in0) )  
        {  
            byte[] array0 = new byte[2];  
  
            int tmp = 0;  
            int count = 0;  
  
            while( pin0.available()>1 && (count = pin0.read(array0)) != -1 )  
            {  
                //两个字节转换为整数   
                tmp = (short)((array0[0] << 8) | (array0[1] & 0xff));  
                tmp = tmp & 0xFFFF;  
  
                //判断是否为BIG5，如果是则显示BIG5中文字  
                if(tmp >= 0xA440 && tmp < 0xFFFF)  
                {  
                    System.out.println("BIG5:" + new String(array0));  
                }  
                else  
                {  
                    //将第二个字节推回流  
                    pin0.unread(array0[1]);  
                    //显示ASCII范围的字符  
                    System.out.println("ASCII: " + (char)array0[0]);  
                }  
            }
			
			if( pin0.available()>0 )
				System.out.println((char)pin0.read());
        }  
        catch(Exception e){ e.printStackTrace(); } 
	}
}
Java基础Demo -- IO 语法器示例

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