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11、java读取文件的几种方式

    博客分类：
  • IO
javajava7 
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package com.tij.io.file;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.Scanner;

/**
 * 读取文件
 * @author guoyoujun
 * @date 2014-3-17
 */
public class JavaReadFile {

	/**
	 * 工作中涉及到文件的时候，有时候我们需要读取阅读它, 现在提供几种不同的方式去读取;
	 * <p>java.nio.file.Files:这是java7中使用的类库,这个类可以读取所有的内容到数组或者读取所有的行到一个列表
	 * <p>java.io.FileReader:可以通过FileReader得到BufferRead从而读取文件的每一行,不过FileReader不支持格式编码所以并不是一种好的方式
	 * <p>java.io.BufferedReader:这是个很好的处理文件读取的类,支持编码、线程安全、默认缓存为8KB
	 * <p>java.util.Scanner:使用这个扫描类可以根据一些正则表达式来读取相应的内容, 默认的是分割内容是空白,是不同步的非线程安全的类
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		String fileName = "/Users/GYJ/webdefault.xml";
		readUsingFileReader(fileName);
		System.out.println("\n");
		readUsingBufferedReader(fileName);
		System.out.println("\n");
		readUsingBufferedReader(fileName, StandardCharsets.UTF_8);
		System.out.println("\n");
		readUsingBufferedReaderJava7(fileName, StandardCharsets.UTF_8);
		System.out.println("\n");
		readUsingFiles(fileName);
		System.out.println("\n");
		readUsingScanner(fileName);
		
	}
	
	/**
	 * FileReader读取
	 * @param fileName
	 * @throws IOException
	 */
	private static void readUsingFileReader(String fileName) throws IOException {
		File file = new File(fileName);
		FileReader fr = new FileReader(file);
		BufferedReader br = new BufferedReader(fr);
		String line;
		while ((line = br.readLine()) != null) {
			System.out.println("read result = " + line);
		}
		br.close();
		fr.close();
	}
	
	/**
	 * BufferedReader读取(支持编码格式)
	 * @param fileName
	 * @param charsetName
	 * @throws IOException
	 */
	private static void readUsingBufferedReader(String fileName, Charset cs) throws IOException  {
		File file = new File(fileName);
		FileInputStream fis = new FileInputStream(file);
		InputStreamReader isr = new InputStreamReader(fis, cs);
		BufferedReader br = new BufferedReader(isr);
		String line;
		while ((line = br.readLine()) != null) {
			System.out.println("read result = " + line);
		}
		br.close();
	}
	
	/**
	 * BufferedReaderd读取文件
	 * @param fileName
	 * @param cs
	 * @throws IOException 
	 */
	private static void readUsingBufferedReaderJava7(String fileName, Charset cs) throws IOException {
		Path path = Paths.get(fileName);
        BufferedReader br = Files.newBufferedReader(path, cs);
        String line;
        while((line = br.readLine()) != null){
            System.out.println("read result = " + line);
        }
        br.close();
	}
	
	/**
	 * BufferedReader读取
	 * @param fileName
	 * @throws IOException
	 */
	private static void readUsingBufferedReader(String fileName) throws IOException {
		File file = new File(fileName);
		FileReader fr = new FileReader(file);
		BufferedReader br = new BufferedReader(fr);
		String line;
		while ((line = br.readLine()) != null) {
			System.out.println("read result = " + line);
		}
		br.close();
		fr.close();
	}
	
	/**
	 * 扫描读取文件
	 * @param fileNme
	 * @throws IOException 
	 */
	private static void readUsingScanner(String fileName) throws IOException {
		Path path = Paths.get(fileName);
        Scanner scanner = new Scanner(path);
        while(scanner.hasNextLine()){
            String line = scanner.nextLine();
            System.out.println("read result = " + line);
        }
	}
	
	/**
	 * 读取文件
	 * @param fileName
	 * @throws IOException
	 */
	private static void readUsingFiles(String fileName) throws IOException {
        Path path = Paths.get(fileName);
        byte[] bytes = Files.readAllBytes(path);
        List<String> allLines = Files.readAllLines(path, StandardCharsets.UTF_8);
        System.out.println(bytes.length);
        System.out.println(allLines.size());
    }
	
}

//因为读取的是同一份文件输出结果就给出一遍的输出结果;
out put============
read result =   <!--                       dumped to a file? [false]                      -->
read result =   <!--                       False if suppressSmap is true                  -->
read result =   <!--                                                                      -->
read result =   <!--   scratchdir          What scratch directory should we use when      -->
read result =   <!--                       compiling JSP pages?  [default work directory  -->
read result =   <!--                       for the current web application]               -->
read result =   <!--                                                                      -->
read result =   <!--   tagpoolMaxSize      The maximum tag handler pool size  [5]         -->
read result =   <!--                                                                      -->
read result =   <!--   xpoweredBy          Determines whether X-Powered-By response       -->
read result =   <!--                       header is added by generated servlet  [false]  -->
read result =   <!--                                                                      -->
read result =   <!-- If you wish to use Jikes to compile JSP pages:                       -->
read result =   <!--   Set the init parameter "compiler" to "jikes".  Define              -->
read result =   <!--   the property "-Dbuild.compiler.emacs=true" when starting Jetty     -->
read result =   <!--   to cause Jikes to emit error messages in a format compatible with  -->
read result =   <!--   Jasper.                                                            -->
read result =   <!--   If you get an error reporting that jikes can't use UTF-8 encoding, -->
read result =   <!--   try setting the init parameter "javaEncoding" to "ISO-8859-1".     -->
read result =   <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  -->
read result =   <servlet
read result =     id="jsp"
read result =   >
read result =     <servlet-name>jsp</servlet-name>
read result =     <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
read result =     <init-param>
read result =       <param-name>logVerbosityLevel</param-name>
read result =       <param-value>DEBUG</param-value>
read result =     </init-param>
read result =     <init-param>
read result =       <param-name>fork</param-name>
read result =       <param-value>false</param-value>
read result =     </init-param>
read result =     <init-param>
read result =       <param-name>xpoweredBy</param-name>
read result =       <param-value>false</param-value>
read result =     </init-param>
read result =     <!-- 
read result =     <init-param>
read result =         <param-name>classpath</param-name>
read result =         <param-value>?</param-value>
read result =     </init-param>
read result =     -->
read result =     <load-on-startup>0</load-on-startup>
read result =   </servlet>
read result =
read result =   <servlet-mapping>
read result =     <servlet-name>jsp</servlet-name>
read result =     <url-pattern>*.jsp</url-pattern>
read result =     <url-pattern>*.jspf</url-pattern>
read result =     <url-pattern>*.jspx</url-pattern>
read result =     <url-pattern>*.xsp</url-pattern>
read result =     <url-pattern>*.JSP</url-pattern>
read result =     <url-pattern>*.JSPF</url-pattern>
read result =     <url-pattern>*.JSPX</url-pattern>
read result =     <url-pattern>*.XSP</url-pattern>
read result =   </servlet-mapping>
read result =
read result =   <!-- ==================================================================== -->
read result =   <!-- Dynamic Servlet Invoker.                                             -->
read result =   <!-- This servlet invokes anonymous servlets that have not been defined   -->
read result =   <!-- in the web.xml or by other means. The first element of the pathInfo  -->
read result =   <!-- of a request passed to the envoker is treated as a servlet name for  -->
read result =   <!-- an existing servlet, or as a class name of a new servlet.            -->
read result =   <!-- This servlet is normally mapped to /servlet/*                        -->
read result =   <!-- This servlet support the following initParams:                       -->
read result =   <!--                                                                      -->
read result =   <!--  nonContextServlets       If false, the invoker can only load        -->
read result =   <!--                           servlets from the contexts classloader.    -->
read result =   <!--                           This is false by default and setting this  -->
read result =   <!--                           to true may have security implications.    -->
read result =   <!--                                                                      -->
read result =   <!--  verbose                  If true, log dynamic loads                 -->
read result =   <!--                                                                      -->
read result =   <!--  *                        All other parameters are copied to the     -->
read result =   <!--                           each dynamic servlet as init parameters    -->
read result =   <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  -->
read result =   <!--
read result =     Uncomment for dynamic invocation <servlet> <servlet-name>invoker</servlet-name> <servlet-class>org.eclipse.jetty.servlet.Invoker</servlet-class> <init-param> <param-name>verbose</param-name>
read result =     <param-value>false</param-value> </init-param> <init-param> <param-name>nonContextServlets</param-name> <param-value>false</param-value> </init-param> <init-param>
read result =     <param-name>dynamicParam</param-name> <param-value>anyValue</param-value> </init-param> <load-on-startup>0</load-on-startup> </servlet> <servlet-mapping> <servlet-name>invoker</servlet-name>
read result =     <url-pattern>/servlet/*</url-pattern> </servlet-mapping>
read result =   -->
read result =
read result =
read result =
read result =   <!-- ==================================================================== -->
read result =   <session-config>
read result =     <session-timeout>30</session-timeout>
read result =   </session-config>
read result =
read result =   <!-- ==================================================================== -->
read result =   <!-- Default MIME mappings                                                -->
read result =   <!-- The default MIME mappings are provided by the mime.properties        -->
read result =   <!-- resource in the org.eclipse.jetty.server.jar file.  Additional or modified  -->
read result =   <!-- mappings may be specified here                                       -->
read result =   <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  -->
read result =   <!-- UNCOMMENT TO ACTIVATE
read result =   <mime-mapping>
read result =     <extension>mysuffix</extension>
read result =     <mime-type>mymime/type</mime-type>
read result =   </mime-mapping>
read result =   -->
read result =
read result =   <!-- ==================================================================== -->
read result =   <welcome-file-list>
read result =     <welcome-file>index.html</welcome-file>
read result =     <welcome-file>index.htm</welcome-file>
read result =     <welcome-file>index.jsp</welcome-file>
read result =   </welcome-file-list>
read result =
read result =   <!-- ==================================================================== -->
read result =   <locale-encoding-mapping-list>
read result =     <locale-encoding-mapping>
read result =       <locale>ar</locale>
read result =       <encoding>ISO-8859-6</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>be</locale>
read result =       <encoding>ISO-8859-5</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>bg</locale>
read result =       <encoding>ISO-8859-5</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>ca</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>cs</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>da</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>de</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>el</locale>
read result =       <encoding>ISO-8859-7</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>en</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>es</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>et</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>fi</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>fr</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>hr</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>hu</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>is</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>it</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>iw</locale>
read result =       <encoding>ISO-8859-8</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>ja</locale>
read result =       <encoding>Shift_JIS</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>ko</locale>
read result =       <encoding>EUC-KR</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>lt</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>lv</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>mk</locale>
read result =       <encoding>ISO-8859-5</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>nl</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>no</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>pl</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>pt</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>ro</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>ru</locale>
read result =       <encoding>ISO-8859-5</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>sh</locale>
read result =       <encoding>ISO-8859-5</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>sk</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>sl</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>sq</locale>
read result =       <encoding>ISO-8859-2</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>sr</locale>
read result =       <encoding>ISO-8859-5</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>sv</locale>
read result =       <encoding>ISO-8859-1</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>tr</locale>
read result =       <encoding>ISO-8859-9</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>uk</locale>
read result =       <encoding>ISO-8859-5</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>zh</locale>
read result =       <encoding>GB2312</encoding>
read result =     </locale-encoding-mapping>
read result =     <locale-encoding-mapping>
read result =       <locale>zh_TW</locale>
read result =       <encoding>Big5</encoding>
read result =     </locale-encoding-mapping>
read result =   </locale-encoding-mapping-list>
read result =
read result =   <security-constraint>
read result =     <web-resource-collection>
read result =       <web-resource-name>Disable TRACE</web-resource-name>
read result =       <url-pattern>/</url-pattern>
read result =       <http-method>TRACE</http-method>
read result =     </web-resource-collection>
read result =     <auth-constraint/>
read result =   </security-constraint>
read result =
read result = </web-app>
read result =
=====================================================================
使用哪一种方式去读取文件取决于项目需求,希望能用到的同学自己决定;
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| 10、java获取文件最后的修改时间
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