[置顶] 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。