java ioutils 写入文件_文件输入输出流工具： IOUtils使用总结
序言
以前寫文件的復制很麻煩，需要各種輸入流，然后讀取line，輸出到輸出流...其實apache.commons.io里面提供了輸入流輸出流的常用工具方法，非常方便。下面就結合源碼，看看IOUTils都有什么用處吧！
常用的靜態變量
在IOUtils中還是有很多常用的一些變量的，比如換行符等等
public static final char DIR_SEPARATOR_UNIX = '/';
public static final char DIR_SEPARATOR_WINDOWS = '\\';
public static final char DIR_SEPARATOR;
public static final String LINE_SEPARATOR_UNIX = "\n";
public static final String LINE_SEPARATOR_WINDOWS = "\r\n";
public static final String LINE_SEPARATOR;
static {
DIR_SEPARATOR = File.separatorChar;
StringBuilderWriter buf = new StringBuilderWriter(4);
PrintWriter out = new PrintWriter(buf);
out.println();
LINE_SEPARATOR = buf.toString();
out.close();
}
常用方法
copy
這個方法可以拷貝流，算是這個工具類中使用最多的方法了。支持多種數據間的拷貝:
copy(inputstream,outputstream)
copy(inputstream,writer)
copy(inputstream,writer,encoding)
copy(reader,outputstream)
copy(reader,writer)
copy(reader,writer,encoding)
copy內部使用的其實還是copyLarge方法。因為copy能拷貝Integer.MAX_VALUE的字節數據，即2^31-1。
copyLarge
這個方法適合拷貝較大的數據流，比如2G以上。
copyLarge(reader,writer) 默認會用1024*4的buffer來讀取
copyLarge(reader,writer,buffer)
內部的細節可以參考：
public static long copyLarge(Reader input, Writer output, char [] buffer) throws IOException {
long count = 0;
int n = 0;
while (EOF != (n = input.read(buffer))) {
output.write(buffer, 0, n);
count += n;
}
return count;
}
這個方法會用一個固定大小的Buffer，持續不斷的讀取數據，然后寫入到輸出流中。
read
從一個流中讀取內容
read(inputstream,byte[])
read(inputstream,byte[],offset,length)
//offset是buffer的偏移值，length是讀取的長度
read(reader,char[])
read(reader,char[],offset,length)
這里我寫了個小例子，可以測試read方法的效果：
@Test
public void readTest(){
try{
byte[] bytes = new byte[4];
InputStream is = IOUtils.toInputStream("hello world");
IOUtils.read(is, bytes);
System.out.println(new String(bytes));
bytes = new byte[10];
is = IOUtils.toInputStream("hello world");
IOUtils.read(is, bytes, 2, 4);
System.out.println(new String(bytes));
} catch (IOException e) {
e.printStackTrace();
}
}
得到的結果是：
hell
□□hell□□□□
readFully
這個方法會讀取指定長度的流，如果讀取的長度不夠，就會拋出異常
readFully(inputstream,byte[])
readFully(inputstream,byte[],offset,length)
readFully(reader,charp[])
readFully(reader,char[],offset,length)
比如：
@Test
public void readFullyTest(){
byte[] bytes = new byte[4];
InputStream is = IOUtils.toInputStream("hello world");
try {
IOUtils.readFully(is,bytes);
System.out.println(new String(bytes));
} catch (IOException e) {
e.printStackTrace();
}
}
輸出
hell
但是如果讀取20個byte,就會出錯了
java.io.EOFException: Length to read: 20 actual: 11
at org.apache.commons.io.IOUtils.readFully(IOUtils.java:2539)
at org.apache.commons.io.IOUtils.readFully(IOUtils.java:2558)
at test.java.IOUtilsTest.readFullyTest(IOUtilsTest.java:22)
...
readLines
readLines方法可以從流中讀取內容，并轉換為String的list
readLines(inputstream)
readLines(inputstream,charset)
readLines(inputstream,encoding)
readLines(reader)
這個方法極大簡化了之前原始的讀取方法：
@Test
public void readLinesTest(){
try{
InputStream is = new FileInputStream("D://test1.txt");
List lines = IOUtils.readLines(is);
for(String line : lines){
System.out.println(line);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
輸出內容：
hello
world
nihao
ioutils
skip
這個方法用于跳過指定長度的流，
skip(inputstream,skip_length)
skip(ReadableByteChannel,skip_length)
skip(reader,skip_length)
例如:
@Test
public void skipTest(){
InputStream is = IOUtils.toInputStream("hello world");
try {
IOUtils.skip(is,4);
System.out.println(IOUtils.toString(is,"utf-8"));
} catch (IOException e) {
e.printStackTrace();
}
}
skipFully
這個方法類似skip，只是如果忽略的長度大于現有的長度，就會拋出異常
skipFully(inputstream,toSkip)
skipFully(readableByteChannel,toSkip)
skipFully(inputstream,toSkip)
例如
@Test
public void skipFullyTest(){
InputStream is = IOUtils.toInputStream("hello world");
try {
IOUtils.skipFully(is,30);
System.out.println(IOUtils.toString(is,"utf-8"));
} catch (IOException e) {
e.printStackTrace();
}
}
write
這個方法可以把數據寫入到輸出流中
write(byte[] data, OutputStream output)
write(byte[] data, Writer output)
write(byte[] data, Writer output, Charset encoding)
write(byte[] data, Writer output, String encoding)
write(char[] data, OutputStream output)
write(char[] data, OutputStream output, Charset encoding)
write(char[] data, OutputStream output, String encoding)
write(char[] data, Writer output)
write(CharSequence data, OutputStream output)
write(CharSequence data, OutputStream output, Charset encoding)
write(CharSequence data, OutputStream output, String encoding)
write(CharSequence data, Writer output)
write(StringBuffer data, OutputStream output)
write(StringBuffer data, OutputStream output, String encoding)
write(StringBuffer data, Writer output)
write(String data, OutputStream output)
write(String data, OutputStream output, Charset encoding)
write(String data, OutputStream output, String encoding)
write(String data, Writer output)
例如
@Test
public void writeTest(){
try {
OutputStream os = new FileOutputStream("E:/test.txt");
IOUtils.write("hello write!",os);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
writeLines
這個方法可以把string的List寫入到輸出流中
writeLines(Collection> lines, String lineEnding, OutputStream output)
writeLines(Collection> lines, String lineEnding, OutputStream output, Charset encoding)
writeLines(Collection> lines, String lineEnding, OutputStream output, String encoding)
writeLines(Collection> lines, String lineEnding, Writer writer)
例如
@Test
public void writeLinesTest() throws IOException {
List lines = new ArrayList();
lines.add("hello");
lines.add("list");
lines.add("to");
lines.add("file");
OutputStream os = new FileOutputStream("E:/test.txt");
IOUtils.writeLines(lines,IOUtils.LINE_SEPARATOR,os);
}
close
關閉URL連接
close(URLConnection conn)
closeQuietly
忽略nulls和異常，關閉某個流
close(URLConnection conn)
closeQuietly(Closeable... closeables)
closeQuietly(Closeable closeable)
closeQuietly(InputStream input)
closeQuietly(OutputStream output)
closeQuietly(Reader input)
closeQuietly(Selector selector)
closeQuietly(ServerSocket sock)
closeQuietly(Socket sock)
closeQuietly(Writer output)
contentEquals
比較兩個流是否相同
contentEquals(InputStream input1, InputStream input2)
contentEquals(Reader input1, Reader input2)
例如
@Test
public void contentEqualsTest(){
InputStream is1 = IOUtils.toInputStream("hello123");
InputStream is2 = IOUtils.toInputStream("hello123");
try {
System.out.println(IOUtils.contentEquals(is1,is2));
} catch (IOException e) {
e.printStackTrace();
}
}
contentEqualsIgnoreEOL
比較兩個流，忽略換行符
contentEqualsIgnoreEOL(Reader input1, Reader input2)
lineIterator
讀取流，返回迭代器
lineIterator(InputStream input, Charset encoding)
lineIterator(InputStream input, String encoding)
lineIterator(Reader reader)
toBufferedInputStream
把流的全部內容放在另一個流中
toBufferedInputStream(InputStream input)
toBufferedInputStream(InputStream input, int size)
toBufferedReader
返回輸入流
toBufferedReader(Reader reader)
toBufferedReader(Reader reader, int size)
toByteArray
返回字節數組
toByteArray(InputStream input)
toByteArray(InputStream input, int size)
toByteArray(InputStream input, long size)
toByteArray(Reader input)
toByteArray(Reader input, Charset encoding)
toByteArray(Reader input, String encoding)
toByteArray(String input)
toByteArray(URI uri)
toByteArray(URL url)
toByteArray(URLConnection urlConn)
toCharArray
返回字符數組
toCharArray(InputStream is)
toCharArray(InputStream is, Charset encoding)
toCharArray(InputStream is, String encoding)
toCharArray(Reader input)
toInputStream
返回輸入流
toInputStream(CharSequence input)
toInputStream(CharSequence input, Charset encoding)
toInputStream(CharSequence input, String encoding)
toInputStream(String input)
toInputStream(String input, Charset encoding)
toInputStream(String input, String encoding)
toString
返回字符串
toString(byte[] input)
toString(byte[] input, String encoding)
toString(InputStream input)
toString(InputStream input, Charset encoding)
toString(InputStream input, String encoding)
toString(Reader input)
toString(URI uri)
toString(URI uri, Charset encoding)
toString(URI uri, String encoding)
toString(URL url)
toString(URL url, Charset encoding)
toString(URL url, String encoding)
總結
以上是生活随笔為你收集整理的java ioutils 写入文件_文件输入输出流工具： IOUtils使用总结的全部內容，希望文章能夠幫你解決所遇到的問題。
- 上一篇： [你必须知道的.NET] 第五回：深入浅
- 下一篇： DotNet程序员是不是最不幸福？