一文帶你了解Java中IO流與Guava的使用

更新時間：2022年11月25日 09:32:32 作者：指北君

Java為我們提供了非常多的操作IO的接口與類，幫助開發(fā)者實現(xiàn)不同源間的數(shù)據(jù)傳輸，比如硬盤文件、網(wǎng)絡(luò)傳輸、應(yīng)用調(diào)用間的數(shù)據(jù)交互與傳遞。今天我們來簡單了解下Java中的流?以及在Guava工具包中，針對IO操作做了什么樣的封裝與設(shè)計

Guava IO

日常系統(tǒng)交互中，文件的上傳下載都是常見的，一般我們會通過jdk提供的IO操作庫幫助我們實現(xiàn)。IO指的是數(shù)據(jù)相對當(dāng)前操作程序的入與出，將數(shù)據(jù)通過輸出流從程序輸出，或者通過輸入流將數(shù)據(jù)（從文件、網(wǎng)絡(luò)、數(shù)據(jù)等）寫入到程序，這里的IO指的是基于流作為載體進(jìn)行數(shù)據(jù)傳輸。如果把數(shù)據(jù)比作合理的水，河就是IO流，也是數(shù)據(jù)的載體。

Java為我們提供了非常多的操作IO的接口與類，幫助開發(fā)者實現(xiàn)不同源間的數(shù)據(jù)傳輸，比如硬盤文件、網(wǎng)絡(luò)傳輸、應(yīng)用調(diào)用間的數(shù)據(jù)交互與傳遞。今天我們來簡單了解下Java中的流以及在Guava工具包中，針對IO操作做了什么樣的封裝與設(shè)計。

常用的流

操作文件的

java.io.FileinputStream/FileOutputStream java.io.FileReader/FileWriter

通用的字節(jié)流

java.io.InputStreamReader/outputStreamWriter

緩沖流

java.io.BufferedReader/BufferedWriter java.io.BufferedInputStream/BufferedOutputStream

數(shù)據(jù)流

java.io.DataInpoutStream/DataOutputStream

功能型的

java.io.PrintWriter/PrintStream

對象序列化相關(guān)的

java.io.ObjectInputStream/ObjectOutputStream

可見，提供的IO對象基本都是成對出現(xiàn)的，用以完成數(shù)據(jù)的輸入輸出，實現(xiàn)程序與外部載體間的數(shù)據(jù)交換

示例

下面我們通過一些常用示例來看看IO的使用的場景與使用方法：

文件復(fù)制
文件的合并
讀取文件內(nèi)容為字符串
字節(jié)數(shù)組轉(zhuǎn)換成流
對象序列化與反序列化
流的轉(zhuǎn)換
......

文件復(fù)制

????@Test
????public?void?copyByBytes()?throws?IOException?{
????????String?root?=?FileTests.class.getResource("/").getPath();

????????FileInputStream?fis?=?new?FileInputStream(new?File(root,"/start.bat"));
????????FileOutputStream?fos?=?new?FileOutputStream(root+"/out2.bat");

????????byte[]?buff?=?new?byte[100];

????????int?b;
????????while?(?(b?=?fis.read(buff))!=-1?){
????????????fos.write(buff,?0,?b);
????????}
????????//?close
????}

文件合并

@Test
????public?void?mergeFiles()?throws?IOException?{
????????File?file1?=?new?File("E:\\_projects\\sucls\\blog\\my_study\\guava\\guava-io\\src\\test\\java\\com\\sucls\\blog\\guava\\io\\category\\FileTests.java");
????????File?file2?=?new?File("E:\\_projects\\sucls\\blog\\my_study\\guava\\guava-io\\src\\test\\java\\com\\sucls\\blog\\guava\\io\\category\\StreamTests.java");

????????Enumeration<InputStream>?ins?=?Collections.enumeration(Arrays.asList(
????????????????new?FileInputStream(file1),
????????????????new?FileInputStream(file2)
????????));

????????SequenceInputStream?sequenceInputStream?=?new?SequenceInputStream(ins);

????????FileOutputStream?fos?=?new?FileOutputStream(root+"/out4");

????????byte[]?buff?=?new?byte[100];

????????int?read;?//?真實讀取到的字節(jié)數(shù)
????????while?(?(read?=?sequenceInputStream.read(buff))?!=-1){
????????????fos.write(buff,?0,?read);
????????}

????????fos.close();
????}

讀取文件內(nèi)容為字符串

????@Test
????public?void?readStringFromFile()?throws?IOException?{
????????FileReader?fileReader?=?new?FileReader(new?File(this.getClass().getResource("/").getPath(),"/start.bat"));

????????StringBuilder?stringBuilder?=?new?StringBuilder();

????????int?i;
????????while?(?(i?=?fileReader.read())!=-1?){
????????????stringBuilder.append(?(char)i?);?//?按字符讀取
????????}

????????System.out.println(?stringBuilder?);?//?文件內(nèi)容
????}

字節(jié)數(shù)組轉(zhuǎn)換成流

????@Test
????public?void?bytesToStream(){
????????byte?[]?data?=?new?byte[1024];?//?來源于其他數(shù)據(jù)源

????????ByteArrayInputStream?inputStream?=?new?ByteArrayInputStream(data);

????????ByteArrayOutputStream?outputStream?=?new?ByteArrayOutputStream();

????????int?v;
????????while?(?(v=inputStream.read())!=-1?){
????????????outputStream.write(v);
????????}

????????System.out.println(?Arrays.toString(?outputStream.toByteArray()?));
????}

對象序列化與反序列化

@Test
????public?void?objectToFile()?throws?IOException?{

????????Person?person?=?new?Person();
????????person.setName("張三").setAge(25);

????????String?root?=?FileTests.class.getResource("/").getPath();

????????FileOutputStream?fos?=?new?FileOutputStream(new?File(root,"/person"));
????????ObjectOutputStream?oos?=?new?ObjectOutputStream(fos);

????????oos.writeObject(person);
????}

????@Test
????public?void?fileToObject()?throws?IOException,?ClassNotFoundException?{
????????String?root?=?FileTests.class.getResource("/").getPath();

????????FileInputStream?fis?=?new?FileInputStream(new?File(root,"/person"));
????????ObjectInputStream?ois?=?new?ObjectInputStream(fis);

????????Person?person?=?(Person)?ois.readObject();
????????System.out.println(?person?);
????}

流的轉(zhuǎn)換將字節(jié)流轉(zhuǎn)換成字符流來操作，同樣以文件復(fù)制為例

????@Test
????public?void?copyByBuffer()?throws?IOException?{
????????String?root?=?FileTests.class.getResource("/").getPath();

????????FileInputStream?fis?=?new?FileInputStream(new?File(root,"/start.bat"));
????????InputStreamReader?isr?=?new?InputStreamReader(fis);
????????BufferedReader?br?=?new?BufferedReader(isr);

????????FileOutputStream?fos?=?new?FileOutputStream(root+"/out3.bat");
????????OutputStreamWriter?osw?=?new?OutputStreamWriter(fos);
????????BufferedWriter?bw?=?new?BufferedWriter(osw);

????????String?line;
????????while?(?(line?=?br.readLine())!=null?){
????????????bw.append(line);
????????????bw.newLine();
????????????bw.flush();
????????}

????????//?close
????}

關(guān)于流的操作非常多，像包括網(wǎng)絡(luò)通信中、音視頻文件處理、流合并等等

Guava中的IO

關(guān)于IO的內(nèi)容并不復(fù)雜，上面的那些例子在很多工具庫中基本都會提供對應(yīng)的API方便開發(fā)者調(diào)用，今天主要看下Guava IO模塊針對流的操作提供了什么樣的封裝

Files

提供對文件快捷讀寫方法其中主要提供了ByteSource、ByteSink、CharSource、CharSink 4個類，分別對應(yīng)按字節(jié)的讀寫與按字符的讀寫，

?/**
?????*?文件復(fù)制
?????*/
????@Test
????public?void?copy()?throws?IOException?{
????????File?from?=?new?File(root,"from");
????????File?to?=?new?File(root,"to");
????????Files.copy(from,to);
????}

????/**
?????*?文件移動
?????*/
????@Test
????public?void?move()?throws?IOException?{
????????File?from?=?new?File(root,"from");
????????File?to?=?new?File(root,"to");
????????Files.move(from,to);
????}

????/**
?????*?按行讀取文件
?????*?@throws?IOException
?????*/
????@Test
????public?void?readLines()?throws?IOException?{
????????File?dest?=?new?File(root,"start.bat");
????????List<String>?lines?=?Files.readLines(dest,?Charset.defaultCharset());
????????lines.forEach(System.out::println);
????}

????/**
?????*?寫入文件
?????*?@throws?IOException
?????*/
????@Test
????public?void?writeToFile()?throws?IOException?{
????????File?dest?=?new?File(root,"demo.txt");
????????Files.write("hello?world!".getBytes(Charset.defaultCharset()),?dest);
????}

????/**
?????*?修改文件更新時間
?????*?@throws?IOException
?????*/
????@Test
????public?void?touch()?throws?IOException?{
????????File?dest?=?new?File(root,"demo.txt");
????????Files.touch(dest);
????}

????/**
?????*?文件的零拷貝
?????*?@throws?IOException
?????*/
????@Test
????public?void?map()?throws?IOException,?URISyntaxException?{
????????File?from?=?new?File(root,"from");
????????File?to?=?new?File(root,"to");
????????Files.touch(to);
????????
????????MappedByteBuffer?fromBuff?=?Files.map(from,?MapMode.READ_ONLY,?1024);
????????//?=>
????????FileChannel?channel?=?FileChannel.open(Paths.get(to.toURI()),?StandardOpenOption.WRITE);

????????channel.write(fromBuff);

????????channel.close();
????}

????/**
?????*?讀文件為字節(jié)數(shù)組
?????*?@throws?IOException
?????*/
????@Test
????public?void?fileAndBytes()?throws?IOException?{
????????File?dest?=?new?File(root,"start.bat");
????????ByteSource?byteSource?=?Files.asByteSource(dest);
????????byte[]?bytes?=?byteSource.read();
????????System.out.println(?bytes?);

????????//?字節(jié)寫入文件，實現(xiàn)復(fù)制
????????File?target?=?new?File(root,?"start2.bat");
????????ByteSink?byteSink?=?Files.asByteSink(target);
????????byteSink.write(bytes);
????}

????@Test
????public?void?wrapper(){
????????File?dest?=?new?File(root,"start.bat");
????????//?作為字節(jié)讀
????????Files.asByteSource(dest);
????????//?作為字節(jié)寫
????????Files.asByteSink(dest);

????????//?作為字符讀
????????Files.asCharSource(dest,?Charset.defaultCharset());
????????//?作為字符寫
????????Files.asCharSink(dest,?Charset.defaultCharset());
????}

其他

管道流

PipedOutputStream PipedInputStream 實現(xiàn)多線程間的數(shù)據(jù)通信；類似生產(chǎn)消費者模式

@Test
????public?void?pipe()?throws?IOException?{
????????PipedOutputStream?pipedOutputStream?=?new?PipedOutputStream();
????????PipedInputStream?pipedInputStream?=?new?PipedInputStream();
????????pipedOutputStream.connect(pipedInputStream);

????????new?Thread(()->{
????????????while?(true){
????????????????String?date?=?new?Date().toString();
????????????????try?{
????????????????????pipedOutputStream.write(?date.getBytes(StandardCharsets.UTF_8)?);
????????????????????pipedOutputStream.flush();
????????????????????TimeUnit.SECONDS.sleep(2);
????????????????}?catch?(IOException?e)?{
????????????????????throw?new?RuntimeException(e);
????????????????}?catch?(InterruptedException?e)?{
????????????????????throw?new?RuntimeException(e);
????????????????}
????????????}
????????}).start();
????????
????????new?Thread(()->{
????????????while?(true){
????????????????byte?[]?buff?=?new?byte[1024];
????????????????try?{
????????????????????int?read?=?pipedInputStream.read(buff);
????????????????????TimeUnit.SECONDS.sleep(4);
????????????????}?catch?(IOException?e)?{
????????????????????throw?new?RuntimeException(e);
????????????????}?catch?(InterruptedException?e)?{
????????????????????throw?new?RuntimeException(e);
????????????????}
????????????????System.out.println(?new?String(buff)?);
????????????}
????????}).start();
????}