java中的string, stream, writer, reader之間的操做

1. 經過OutputStream將字符類的數據輸出到String

有些接口的入參是OutputStream, 若是經過這樣的接口將數據寫入到一個String中, 能夠這樣操做

ByteArrayOutputStream out = new ByteArrayOutputStream();
print(out); //輸出到out
out.toString();//轉換成String

2. 將OutputString封裝成Writer來實現更豐富的操做

ByteArrayOutputStream out = new ByteArrayOutputStream();
OutputStreamWriter writer1 = new OutputStreamWriter(out);//最基本的方式
PrintStream writer2 = new PrintStream(out); //更加豐富的接口, 日常使用的System.out就是這個類型

3. 將Writer封裝成OutputStream

JDK中好像有相關的接口, 可是apache的commons-io實現了, WriterOutputStream

4. 從InputStream讀取String

public static String readString(InputStream in) throws IOException{
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		int i;
		while ((i = in.read()) != -1) {  
		    baos.write(i);  
		}  
		return baos.toString();  		
	}

5. 將String封裝成Reader

String input = "java -jar xx.jar -a param_a";
		StringReader reader = new StringReader(input);
		CharArrayReader reader2 = new CharArrayReader(input.toCharArray());
		BufferedReader reader3 = new BufferedReader(reader); //能夠實現按行讀

6. 將InputStream封裝成Reader

FileInputStream fin = new FileInputStream("xxx.txt");
		InputStreamReader reader0 = new InputStreamReader(fin);
		FileReader reader1 = new FileReader("xxx.txt");  //直接將文件封裝成reader

7. 將Reader封裝成InputStream

使用apache的commons-io庫, ReaderInputStream

8. StringWriter與CharArrayWriter的區別

StringWriter是對StringBuffer的再次封裝, 它是線程安全的

CharArrayWriter所有是它本身實現的, 沒有藉助其它的類, 它也是線程安全的

兩者在性能上也沒有太大的差異, CharArrayWriter效率比StringBuffer高那麼一丁點兒, 正常狀況下, 看不出差異.

使用CharArrayWriter的惟一的好處可能就是獲取char[]比較方便, 它有現成的接口.