think in java interview-高级开发人员面试宝典(八)

面经出了7套，收到许多读者的Email，有许多人说了，这些基础知识是不是为了后面进一步的”通向架构师的道路“做准备的？

对的，你们没有猜错，就是这样的，我一直在酝酿后面的”通向架构师的道路“如何开章。

说实话，我已经在肚子里准备好的后面的”通向架构师的道路“的内容自己觉得如果一下子全拿出来的话，很多人吃不消，因为架构越来越复杂，用到的知识越来越多，而且很多都是各知识点的混合应用。

所以，先以这几套面经来铺路，我们把基础打实了，才能把大楼造的更好。因为，一个架构师首先他是一个程序员，他的基础知识必须非常的扎实，API对于架构师来说已经不太需要eclipse的code insight(即在eclipse编辑器里打一个小点点就可以得到后面的函数），尤其是一些常用的JAVA API来说，是必须熟记于心的。

下面我们继续来几天面经，顺带便复习一下JAVA和数据库的一些基础。

Java IO流的复习

大家平时J2EE写多了，JAVA的IO操作可能都已经生疏了，面试时如果来上这么几道，是不是有点”其实这个问题很简单，可是我就是想不起来“的感觉啊？

呵呵！

JAVA的IO操作太多，我这边挑腾迅，盛大和百度的几道面试题，并整理出答案来供大家参考。

InputFromConsole

这个最简单不过了，从console接受用户输入的字符，如和用户有交互的命令行。

如果你不复习的话，嘿嘿，还真答不出，来看：

package org.sky.io;public class InputFromConsole {/** * @param args */public static void main(String[] args) throws Exception {int a = 0;byte[] input = new byte[1024];System.in.read(input);System.out.println("your input is: " + new String(input));}}

ListDir

列出给出路径下所有的目录，包括子目录

package org.sky.io;import java.io.*;public class ListMyDir {/** * @param args */public static void main(String[] args) {String fileName = "D:" + File.separator + "tomcat2";File f = new File(fileName);File[] fs = f.listFiles();for (int i = 0; i < fs.length; i++) {System.out.println(fs[i].getName());}}}

咦，上面这个程序只列出了一层目录，我们想连子目录一起List出来怎么办？

ListMyDirWithSubDir

package org.sky.io;import java.io.*;public class ListMyDirWithSubDir {/** * @param args */public void print(File f) {if (f != null) {if (f.isDirectory()) {File[] fileArray = f.listFiles();if (fileArray != null) {for (int i = 0; i < fileArray.length; i++) {print(fileArray[i]);}}} else {System.out.println(f);}}}public static void main(String[] args) {String fileName = "D:" + File.separator + "tomcat2";File f = new File(fileName);ListMyDirWithSubDir listDir = new ListMyDirWithSubDir();listDir.print(f);}}

InputStreamDemo

从外部读入一个文件

package org.sky.io;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.InputStream;import java.io.OutputStream;public class InputStreamDemo {public void readFile(String fileName) {File srcFile = new File(fileName);InputStream in = null;try {in = new FileInputStream(srcFile);byte[] b = new byte[(int) srcFile.length()];for (int i = 0; i < b.length; i++) {b[i] = (byte) in.read();}System.out.println(new String(b));} catch (Exception e) {e.printStackTrace();} finally {try {if (in != null) {in.close();in = null;}} catch (Exception e) {}}}public static void main(String[] args) {InputStreamDemo id = new InputStreamDemo();String src = "D:" + File.separator + "hello.txt";id.readFile(src);}}

OutputStreamDemo

讲完了InputStream来讲OutputStream，输出内容至外部的一个文件

package org.sky.io;import java.io.*;public class OutputStreamDemo {public void writeWithByte() {String fileName = "D:" + File.separator + "hello.txt";OutputStream out = null;File f = new File(fileName);try {out = new FileOutputStream(f, true);String str = "   [Publicity ministry of ShangHai Municipal committee of CPC]";byte[] b = str.getBytes();out.write(b);} catch (Exception e) {e.printStackTrace();} finally {try {if (out != null) {out.close();out = null;}} catch (Exception e) {}}}public void writeWithByteArray() {String fileName = "D:" + File.separator + "hello.txt";OutputStream out = null;File f = new File(fileName);try {out = new FileOutputStream(f, true);String str = "   [hello with byte yi ge ge xie]";byte[] b = str.getBytes();for (int i = 0; i < b.length; i++) {out.write(b[i]);}} catch (Exception e) {e.printStackTrace();} finally {try {if (out != null) {out.close();out = null;}} catch (Exception e) {}}}public static void main(String[] args) {OutputStreamDemo od = new OutputStreamDemo();od.writeWithByte();od.writeWithByteArray();}}

这个Demo里分别用了”writeWithByte“和 ”writeWithByteArray“两种方法，注意查看

CopyFile

我们讲完了InputStream和OutputStream，我们就可以自己实现一个File Copy的功能了，来看

package org.sky.io;import java.io.*;public class CopyFile {public void copy(String src, String des) {File srcFile = new File(src);File desFile = new File(des);InputStream in = null;OutputStream out = null;try {in = new FileInputStream(srcFile);out = new FileOutputStream(desFile);byte[] b = new byte[(int) srcFile.length()];for (int i = 0; i < b.length; i++) {b[i] = (byte) in.read();}out.write(b);System.out.println("copied [" + srcFile.getName() + "]    with    "+ srcFile.length());} catch (Exception e) {e.printStackTrace();} finally {try {if (out != null) {out.close();out = null;}} catch (Exception e) {}try {if (in != null) {in.close();in = null;}} catch (Exception e) {}}}public static void main(String[] args) {CopyFile cp = new CopyFile();String src = "D:" + File.separator + "UltraEdit.zip";String des = "D:" + File.separator + "UltraEdit_Copy.zip";long sTime = System.currentTimeMillis();cp.copy(src, des);long eTime = System.currentTimeMillis();System.out.println("Total spend: " + (eTime - sTime));}}

运行后显示：

来看我们被Copy的这个文件的大小：

也不大，怎么用了7秒多？

原是我们没有使用Buffer这个东西，即缓冲，性能会相差多大呢？来看

BufferInputStreamDemo

package org.sky.io;import java.io.*;public class BufferInputStreamDemo {/** * @param args */public void copy(String src, String des) {File srcFile = new File(src);File desFile = new File(des);BufferedInputStream bin = null;BufferedOutputStream bout = null;try {bin = new BufferedInputStream(new FileInputStream(srcFile));bout = new BufferedOutputStream(new FileOutputStream(desFile));byte[] b = new byte[1024];while (bin.read(b) != -1) {bout.write(b);}bout.flush();System.out.println("copied [" + srcFile.getName() + "]    with    "+ srcFile.length());} catch (Exception e) {e.printStackTrace();} finally {try {if (bout != null) {bout.close();bout = null;}} catch (Exception e) {}try {if (bin != null) {bin.close();bin = null;}} catch (Exception e) {}}}public static void main(String[] args) {BufferInputStreamDemo bd = new BufferInputStreamDemo();String src = "D:" + File.separator + "UltraEdit.zip";String des = "D:" + File.separator + "UltraEdit_Copy.zip";long sTime = System.currentTimeMillis();bd.copy(src, des);long eTime = System.currentTimeMillis();System.out.println("Total spend: " + (eTime - sTime));}}

我们Copy同样一个文件，用了多少时间呢？来看！

丫只用了14毫秒，CALL！！！

ByteArrayDemo

来看看使用ByteArray输出文件吧

package org.sky.io;import java.io.*;public class ByteArrayDemo {/** * @param args */public void testByteArray() {String str = "HOLLYJESUS";ByteArrayInputStream input = null;ByteArrayOutputStream output = null;try {input = new ByteArrayInputStream(str.getBytes());output = new ByteArrayOutputStream();int temp = 0;while ((temp = input.read()) != -1) {char ch = (char) temp;output.write(Character.toLowerCase(ch));}String outStr = output.toString();input.close();output.close();System.out.println(outStr);} catch (Exception e) {e.printStackTrace();} finally {try {if (output != null) {output.close();output = null;}} catch (Exception e) {}try {if (input != null) {input.close();input = null;}} catch (Exception e) {}}}public static void main(String[] args) {ByteArrayDemo bd = new ByteArrayDemo();bd.testByteArray();}}

RandomAccess

有种输出流叫Random，你们还记得吗？学习时记得的，工作久了，HOHO，忘了，它到底有什么特殊的地方呢？来看：

package org.sky.io;import java.io.*;public class RandomAccess {public void writeToFile() {String fileName = "D:" + File.separator + "hello.txt";RandomAccessFile randomIO = null;try {File f = new File(fileName);randomIO = new RandomAccessFile(f, "rw");randomIO.writeBytes("asdsad");randomIO.writeInt(12);randomIO.writeBoolean(true);randomIO.writeChar('A');randomIO.writeFloat(1.21f);randomIO.writeDouble(12.123);} catch (Exception e) {e.printStackTrace();} finally {try {if (randomIO != null) {randomIO.close();randomIO = null;}} catch (Exception e) {}}}public static void main(String[] args) {RandomAccess randomA = new RandomAccess();randomA.writeToFile();}}

它输出后的文件是怎么样的呢？

PipeStream

这个流很特殊，我们在线程操作时，两个线程都在运行，这时通过发送一个指令让某个线程do something，我们在以前的jdk1.4中为了实现这样的功能，使用的就是这个PipeStream

先来看两个类，一个叫SendMessage，即发送一个指令。一个叫ReceiveMessage，用于接受指令。

SendMessage

package org.sky.io;import java.io.*;public class SendMessage implements Runnable {private PipedOutputStream out = null;public PipedOutputStream getOut() {return this.out;}public SendMessage() {this.out = new PipedOutputStream();}public void send() {String msg = "start";try {out.write(msg.getBytes());} catch (Exception e) {e.printStackTrace();} finally {try {if (out != null) {out.close();out = null;}} catch (Exception e) {}}}public void run() {try {System.out.println("waiting for signal...");Thread.sleep(2000);send();} catch (Exception e) {e.printStackTrace();}}}

ReceiveMessage

package org.sky.io;import java.io.*;public class ReceiveMessage implements Runnable {private PipedInputStream input = null;public PipedInputStream getInput() {return this.input;}public ReceiveMessage() {this.input = new PipedInputStream();}private void receive() {byte[] b = new byte[1000];int len = 0;String msg = "";try {len = input.read(b);msg = new String(b, 0, len);if (msg.equals("start")) {System.out.println("received the start message, receive now can do something......");Thread.interrupted();}} catch (Exception e) {e.printStackTrace();} finally {try {if (input != null) {input.close();input = null;}} catch (Exception e) {}}}public void run() {try {receive();} catch (Exception e) {}}}

如何使用这两个类呢？

TestPipeStream

package org.sky.io;public class TestPipeStream {/** * @param args */public static void main(String[] args) {SendMessage send = new SendMessage();ReceiveMessage receive = new ReceiveMessage();try {send.getOut().connect(receive.getInput());Thread t1 = new Thread(send);Thread t2 = new Thread(receive);t1.start();t2.start();} catch (Exception e) {e.printStackTrace();}}}

注意这边有一个send.getOut().connect(receive.getInput());

这个方法就把两个线程”connect“起来了。

Serializable的IO操作

把一个类序列化到磁盘上，怎么做？

先来看我们要序列化的一个Java Bean

Person

package org.sky.io;import java.io.Serializable;public class Person implements Serializable {private String name = "";private String age = "";private String personId = "";public String getName() {return name;}public void setName(String name) {this.name = name;}public String getAge() {return age;}public void setAge(String age) {this.age = age;}public String getPersonId() {return personId;}public void setPersonId(String personId) {this.personId = personId;}public String getCellPhoneNo() {return cellPhoneNo;}public void setCellPhoneNo(String cellPhoneNo) {this.cellPhoneNo = cellPhoneNo;}private String cellPhoneNo = "";}

下面来看序列化的操作

SerializablePersonToFile

package org.sky.io;import java.io.*;import java.util.*;public class SerializablePersonToFile {/** * @param args */private List<Person> initList() {List<Person> userList = new ArrayList<Person>();Person loginUser = new Person();loginUser.setName("sam");loginUser.setAge("30");loginUser.setCellPhoneNo("13333333333");loginUser.setPersonId("111111111111111111");userList.add(loginUser);loginUser = new Person();loginUser.setName("tonny");loginUser.setAge("31");loginUser.setCellPhoneNo("14333333333");loginUser.setPersonId("111111111111111111");userList.add(loginUser);loginUser = new Person();loginUser.setName("jim");loginUser.setAge("28");loginUser.setCellPhoneNo("15333333333");loginUser.setPersonId("111111111111111111");userList.add(loginUser);loginUser = new Person();loginUser.setName("Simon");loginUser.setAge("30");loginUser.setCellPhoneNo("17333333333");loginUser.setPersonId("111111111111111111");userList.add(loginUser);return userList;}private  void serializeFromFile() {FileInputStream fs = null;ObjectInputStream ois = null;try {fs = new FileInputStream("person.txt");ois = new ObjectInputStream(fs);List<Person> userList = (ArrayList<Person>) ois.readObject();for (Person p : userList) {System.out.println(p.getName() + "   " + p.getAge() + "   "+ p.getCellPhoneNo() + "   " + p.getCellPhoneNo());}} catch (Exception ex) {ex.printStackTrace();} finally {try {if (ois != null) {ois.close();}} catch (Exception e) {}try {if (fs != null) {fs.close();}} catch (Exception e) {}}}private void serializeToFile() {List<Person> userList = new ArrayList<Person>();userList = initList();FileOutputStream fs = null;ObjectOutputStream os = null;try {fs = new FileOutputStream("person.txt");os = new ObjectOutputStream(fs);os.writeObject(userList);} catch (Exception ex) {ex.printStackTrace();} finally {try {if (os != null) {os.close();}} catch (Exception e) {}try {if (fs != null) {fs.close();}} catch (Exception e) {}}}public static void main(String[] args) {SerializablePersonToFile sf = new SerializablePersonToFile();sf.serializeToFile();sf.serializeFromFile();}}

这边先把Person输出到Person.txt，再从Person.txt里反序列化出这个Person的Java Bean。

先讲这么些吧！

Java的流操作还有很多，这些是经常会被面试到的，很基础，因此经常被考到。

以前听一个读IT的同学说过，这些IO操作，就算没有Eclipse编辑器的话，用文本编辑器也应该能够写出来，你写不出只能代表你的基础太弱了。