createtempfile，createNewFile和createTempFile
亲爱的读者们，你是否对createtempfile和createNewFile和createTempFile的关系感到好奇？在本文中，我将深入探讨它们之间的联系，让你对此有更深刻的理解。
如何建立Temp这个文件夹
Temp文件夹的问题WINDOWS/Temp里的是Windows在正常的使用过程中产生的系统临时文件，可以把它们删除。不会影响系统的。在系统使用中有些文件没法删除也很正常的。Temp文件夹是什么文件夹？
C:\Documents and Settings用户里有个Local Settings文件夹，Local Settings里的Temp文件夹可以删除吗？Temp是什么文件夹？C盘里所有的TEMP文件夹都是临时文件夹文件夹可以删除为节省可用空间，你可以在启动电脑的时候自动清空Temp文件夹中的文件。方法是选择“开始｜运行”，键入“sysedit”，单击“确定”，启动“系统配置编辑程序”，进入“c:＼autoexec.bat”窗口，在文本末尾加入：deltree/y C:＼Windows＼Temp，保存并退出。此后，在你每次启动计算机后就会得到一个空白的Temp文件夹了。怎样更改TEMP文件夹的位置在非系统盘如D盘下新建文件夹Temp，然后右击“我的电脑”，选择“属性→高级→环境变量”，在弹出的“环境变量”窗口分别双击“用户变量”下的TEMP、TMP变量，把原来的“%USERPROFILE%\Local Settings\Temp”都修改为“D:\Temp”就ok了。
createNewFile和createTempFile
File.createNewFilefile类的createnewfile根据抽象路径创建一个新的空文件，当抽象路径制定的文件存在时，创建失败
File.createTempFile
的用途是你想要建立一个档案暂时使用，但是你不在乎其精确的档案名，只要不覆盖到已存在的档案时。可以制定
临时文件
的文件名前缀、后缀及文件所在的目录，如果不指定目录，则存放在系统的
临时文件夹
下。
JAVA里Flie类的creatnewfile与creattempfile有什么不同
后者的文件建立在默认的临时文件目录中不在当前目录
createNewFile
public boolean createNewFile()
throws IOException当且仅当不存在具有此抽象路径名指定名称的文件时，不可分地创建一个新的空文件。检查文件是否存在，若不存在则创建该文件，这是单个操作，对于其他所有可能影响该文件的文件系统活动来说，该操作是不可分的。
createTempFile
public static File createTempFile(String prefix,
String suffix)
throws IOException在默认临时文件目录中创建一个空文件，使用给定前缀和后缀生成其名称。调用此方法等同于调用 createTempFile(prefix, suffix, null)。
参数：
prefix-用于生成文件名的前缀字符串；必须至少是三字符长
suffix-用于生成文件名的后缀字符串；可以为 null，在这种情况下，将使用后缀".tmp"
返回：
表示新建空文件的抽象路径名
java程序如何调用Graphviz
网上有别人已经写好的一个GraphViz.java类。java可以直接调用这个类实现画图功能，但是使用这个类的前提是你的电脑已经装了GraphViz软件，你可以在http://www.graphviz.org/Gallery.php下载windows版本，装完后，找到dot.exe所在的路径，我电脑上的是D:\Program Files\Graphviz2.30\bin\dot.exe,
将GraphViz.java中的这一路径改成你电脑上的路径，基本上就可以用了。
package Graphoutput;
// GraphViz.java- a simple API to call dot from Java programs
/*$Id$*/
/*
******************************************************************************
**
*(c) Copyright 2003 Laszlo Szathmary*
**
* This program is free software; you can redistribute it and/or modify it*
* under the terms of the GNU Lesser General Public License as published by*
* the Free Software Foundation; either version 2.1 of the License, or*
*(at your option) any later version.*
**
* This program is distributed in the hope that it will be useful, but*
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY*
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public*
* License for more details.*
**
* You should have received a copy of the GNU Lesser General Public License*
* along with this program; if not, write to the Free Software Foundation,*
* Inc., 675 Mass Ave, Cambridge, MA 02139, USA.*
**
******************************************************************************
*/
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.InputStreamReader;
/**
*<dl>
*<dt>Purpose: GraphViz Java API
*<dd>
*
*<dt>Description:
*<dd> With this Java class you can simply call dot
* from your Java programs
*<dt>Example usage:
*<dd>
*<pre>
* GraphViz gv= new GraphViz();
* gv.addln(gv.start_graph());
* gv.addln("A-> B;");
* gv.addln("A-> C;");
* gv.addln(gv.end_graph());
* System.out.println(gv.getDotSource());
*
* String type="gif";
* File out= new File("out."+ type);// out.gif in this example
* gv.writeGraphToFile( gv.getGraph( gv.getDotSource(), type), out);
*</pre>
*</dd>
*
*</dl>
*
*@version v0.4, 2011/02/05(February)-- Patch of Keheliya Gallaba is added. Now you
* can specify the type of the output file: gif, dot, fig, pdf, ps, svg, png, etc.
*@version v0.3, 2010/11/29(November)-- Windows support+ ability
* to read the graph from a text file
*@version v0.2, 2010/07/22(July)-- bug fix
*@version v0.1, 2003/12/04(December)-- first release
*@author Laszlo Szathmary(<a rel="external nofollow" href="jabba.laci@gmail.com">jabba.laci@gmail.com</a>)
*/
public class GraphViz
{
/**
* The dir. where temporary files will be created.
*/
//private static String TEMP_DIR="/tmp";// Linux
private static String TEMP_DIR="c:/temp";// Windows
/**
* Where is your dot program located? It will be called externally.
*/
// private static String DOT="/usr/bin/dot";// Linux
private static String DOT="D:\\Program Files\\Graphviz2.30\\bin\\dot.exe";// Windows
/**
* The source of the graph written in dot language.
*/
private StringBuilder graph= new StringBuilder();
/**
* Constructor: creates a new GraphViz object that will contain
* a graph.
*/
public GraphViz(){
}
/**
* Returns the graph's source description in dot language.
*@return Source of the graph in dot language.
*/
public String getDotSource(){
return graph.toString();
}
/**
* Adds a string to the graph's source(without newline).
*/
public void add(String line){
graph.append(line);
}
/**
* Adds a string to the graph's source(with newline).
*/
public void addln(String line){
graph.append(line+"\n");
}
/**
* Adds a newline to the graph's source.
*/
public void addln(){
graph.append('\n');
}
/**
* Returns the graph as an image in binary format.
*@param dot_source Source of the graph to be drawn.
*@param type Type of the output image to be produced, e.g.: gif, dot, fig, pdf, ps, svg, png.
*@return A byte array containing the image of the graph.
*/
public byte[] getGraph(String dot_source, String type)
{
File dot;
byte[] img_stream= null;
try{
dot= writeDotSourceToFile(dot_source);
if(dot!= null)
{
img_stream= get_img_stream(dot, type);
if(dot.delete()== false)
System.err.println("Warning:"+ dot.getAbsolutePath()+" could not be deleted!");
return img_stream;
}
return null;
} catch(java.io.IOException ioe){ return null;}
}
/**
* Writes the graph's image in a file.
*@param img A byte array containing the image of the graph.
*@param file Name of the file to where we want to write.
*@return Success: 1, Failure:-1
*/
public int writeGraphToFile(byte[] img, String file)
{
File to= new File(file);
return writeGraphToFile(img, to);
}
/**
* Writes the graph's image in a file.
*@param img A byte array containing the image of the graph.
*@param to A File object to where we want to write.
*@return Success: 1, Failure:-1
*/
public int writeGraphToFile(byte[] img, File to)
{
try{
FileOutputStream fos= new FileOutputStream(to);
fos.write(img);
fos.close();
} catch(java.io.IOException ioe){ ioe.printStackTrace();return-1;}
return 1;
}
/**
* It will call the external dot program, and return the image in
* binary format.
*@param dot Source of the graph(in dot language).
*@param type Type of the output image to be produced, e.g.: gif, dot, fig, pdf, ps, svg, png.
*@return The image of the graph in.gif format.
*/
private byte[] get_img_stream(File dot, String type)
{
File img;
byte[] img_stream= null;
try{
img= File.createTempFile("graph_","."+type, new File(GraphViz.TEMP_DIR));
Runtime rt= Runtime.getRuntime();
// patch by Mike Chenault
String[] args={DOT,"-T"+type, dot.getAbsolutePath(),"-o", img.getAbsolutePath()};
Process p= rt.exec(args);
p.waitFor();
FileInputStream in= new FileInputStream(img.getAbsolutePath());
img_stream= new byte[in.available()];
in.read(img_stream);
// Close it if we need to
if( in!= null) in.close();
if(img.delete()== false)
System.err.println("Warning:"+ img.getAbsolutePath()+" could not be deleted!");
}
catch(java.io.IOException ioe){
System.err.println("Error: in I/O processing of tempfile in dir"+ GraphViz.TEMP_DIR+"\n");
System.err.println(" or in calling external command");
ioe.printStackTrace();
}
catch(java.lang.InterruptedException ie){
System.err.println("Error: the execution of the external program was interrupted");
ie.printStackTrace();
}
return img_stream;}
/**
* Writes the source of the graph in a file, and returns the written file
* as a File object.
*@param str Source of the graph(in dot language).
*@return The file(as a File object) that contains the source of the graph.
*/
public File writeDotSourceToFile(String str) throws java.io.IOException
{
File temp;
try{
temp= File.createTempFile("graph_",".dot.tmp", new File(GraphViz.TEMP_DIR));
FileWriter fout= new FileWriter(temp);
fout.write(str);
fout.close();
}
catch(Exception e){
System.err.println("Error: I/O error while writing the dot source to temp file!");
return null;
}
return temp;
}
/**
* Returns a string that is used to start a graph.
*@return A string to open a graph.
*/
public String start_graph(){
return"digraph G{";
}
/**
* Returns a string that is used to end a graph.
*@return A string to close a graph.
*/
public String end_graph(){
return"}";
}
/**
* Read a DOT graph from a text file.
*
*@param input Input text file containing the DOT graph
* source.
*/
public void readSource(String input)
{
StringBuilder sb= new StringBuilder();
try
{
FileInputStream fis= new FileInputStream(input);
DataInputStream dis= new DataInputStream(fis);
BufferedReader br= new BufferedReader(new InputStreamReader(dis));
String line;
while((line= br.readLine())!= null){
sb.append(line);
}
dis.close();
}
catch(Exception e){
System.err.println("Error:"+ e.getMessage());
}
this.graph= sb;
}
}// end of class GraphViz
通过下面这个类调用graphViz.java
import java.io.File;
public class Proba
{
public static void main(String[] args)
{
Proba p= new Proba();
p.start();
// p.start2();
}
/**
* Construct a DOT graph in memory, convert it
* to image and store the image in the file system.
*/
private void start()
{
GraphViz gv= new GraphViz();
gv.addln(gv.start_graph());
gv.addln("A-> B;");
gv.addln("A-> C;");
gv.addln(gv.end_graph());
System.out.println(gv.getDotSource());
String type="gif";
// String type="dot";
// String type="fig";// open with xfig
// String type="pdf";
// String type="ps";
// String type="svg";// open with inkscape
// String type="png";
// String type="plain";
File out= new File("/tmp/out."+ type);// Linux
// File out= new File("c:/eclipse.ws/graphviz-java-api/out."+ type);// Windows
gv.writeGraphToFile( gv.getGraph( gv.getDotSource(), type), out);
}
/**
* Read the DOT source from a file,
* convert to image and store the image in the file system.
*/
private void start2()
{
// String dir="/home/jabba/eclipse2/laszlo.sajat/graphviz-java-api";// Linux
// String input= dir+"/sample/simple.dot";
String input="c:/eclipse.ws/graphviz-java-api/sample/simple.dot";// Windows
GraphViz gv= new GraphViz();
gv.readSource(input);
System.out.println(gv.getDotSource());
String type="gif";
// String type="dot";
// String type="fig";// open with xfig
// String type="pdf";
// String type="ps";
// String type="svg";// open with inkscape
// String type="png";
// String type="plain";
File out= new File("/tmp/simple."+ type);// Linux
// File out= new File("c:/eclipse.ws/graphviz-java-api/tmp/simple."+ type);// Windows
gv.writeGraphToFile( gv.getGraph( gv.getDotSource(), type), out);
}
}
关于createtempfile到此分享完毕，希望能帮助到您。