[Java IO] Basics: Reading files

1. Read the file path string 1.1 using ClassLoaderclass method to get the file path

System. out. println(This. GetClass(). getClassLoader(). GetResource("."). GetPath());//Get the project's class file pathSystem. out. println(This. GetClass(). getClassLoader(). GetResource(""). GetPath());//Get the project's class file pathSystem. out. println(This. GetClass(). GetResource("/"). GetPath());//Get the project's class file pathSystem. out. println(Thread. CurrentThread(). Getcontextclassloader(). GetResource(""). GetPath());System. out. println(Thread. CurrentThread(). Getcontextclassloader(). GetResource("."). GetPath());System. out. println(This. GetClass(). GetResource(""). GetPath())//★ Get the package path where the current file is locatedSystem. out. println(This. GetClass(). GetResource("."). GetPath())//★ Get the package path where the current file is located

Results:
/d:/workspace/dgcerttest/build/classes/
/d:/workspace/dgcerttest/build/classes/
/d:/workspace/dgcerttest/build/classes/
/d:/workspace/dgcerttest/build/classes/
/d:/workspace/dgcerttest/build/classes/
/d:/workspace/dgcerttest/build/classes/com/test/
/d:/workspace/dgcerttest/build/classes/com/test/

1.2 By getCanonicalPath()And getAbsolutePath()Get file path

new File("");// 设定为当前文件夹 System.out.println(directory.getCanonicalPath());// 获取标准的路径 System.out.println(directory.getAbsolutePath());// 获取绝对路径 //结果：D:\workspace\java_basenew File("/");// 设定为当前文件夹 System.out.println(panFu.getCanonicalPath());//得到所在磁盘System.out.println(directory.getAbsolutePath());// 获取绝对路径 //结果：D:\

2. Get IO stream via file path 2.1 FileInputStream: Reads a file at a specific location on the local disk

String path= "D:\HwTemp\dongguan_test\test.xml";
FileInputStream fis=new FileInputStream (path);
But in this way in the change of environmental testing and re-copied to someone else's disk, not put in the project, with the project relative path to access convenience.
This works in a different environment can be directly run, that isString ->FileInputStream

//project path + relative path to project (with) String path = System.getproperty ("User.dir" ) + "\\  src\\  file.txt";//Will all the above-obtained path "\ " converted to" \\  "path = Path.replaceall (" \\  \\ ", "\\  \\  \\  \\ "); SYSTEM.OUT.PRINTLN (path); FileInputStream fis = new FileInputStream (path),//d:\\  Workspace\\  java_base\\  src\\  file.txt  

Note: The string \\ represents a " \ " but the first parameter in the Relaceall is a regular expression, which in regular \\\\ notation represents a " \ "
But System.getProperty("user.dir") if the Java code is placed in a JSP, it will be the IDE's installation path. So the code cannot be used in a JSP page

2.2 InputStream: Method get****AsStreamRead the file in this project:

The class method returns InputStream
Reference documentation: Java reads files in the project

• Method One: (not validated) place the XML file in the Web-inf directory, and then

is"/WEB-INF/xmlfile.xml" );

• Method Two: Put the XML file in the/web-inf/classes directory or classpath jar package, you can use ClassLoader static method Getsystemresourceasstream (String s) read;

String s_xmlpath="com/spf/web/ext/hotspot/hotspotxml/hotspot.xml"in=ClassLoader.getSystemResourceAsStream(s_xmlpath);

• Method Three: XML at random under a package path

String s_xmlpath="com/spf/web/ext/hotspot/hotspotxml/hotspot.xml";ClassLoader classLoader=HotspotXmlParser.class.getClassLoader();in=classLoader.getResourceAsStream(s_xmlpath);

3. Annex 3.1, annex 1: Obtaining system parameters via System.getproperties ()

Properties Props=system. GetProperties();//System PropertiesSystem. out. println("Java version of the runtime environment:"+props. GetProperty("Java.version"));System. out. println("Java Operating Environment vendor:"+props. GetProperty("Java.vendor"));System. out. println("Java Vendor's URL:"+props. GetProperty("Java.vendor.url"));System. out. println("Installation path for Java:"+props. GetProperty("Java.home"));System. out. println("Java version of the virtual machine specification:"+props. GetProperty("Java.vm.specification.version"));System. out. println("Java's virtual Machine specification provider:"+props. GetProperty("Java.vm.specification.vendor"));System. out. println("Java's virtual Machine specification Name:"+props. GetProperty("Java.vm.specification.name"));System. out. println("virtual machine implementation version of Java:"+props. GetProperty("Java.vm.version"));System. out. println("Java Virtual machine Implementation provider:"+props. GetProperty("Java.vm.vendor"));System. out. println("Java Virtual machine implementation name:"+props. GetProperty("Java.vm.name"));System. out. println("Java Runtime Environment Specification version:"+props. GetProperty("Java.specification.version"));System. out. println("Java Runtime Environment Specification vendor:"+props. GetProperty("Java.specification.vender"));System. out. println("Java Runtime Environment Specification name:"+props. GetProperty("Java.specification.name"));System. out. println("Java class format version number:"+props. GetProperty("Java.class.version"));System. out. println("Classpath for Java:"+props. GetProperty("Java.class.path"));System. out. println("List of paths searched when loading library:"+props. GetProperty("Java.library.path"));System. out. println("Default temporary file path:"+props. GetProperty("Java.io.tmpdir"));System. out. println("path to one or more extended directories:"+props. GetProperty("Java.ext.dirs"));System. out. println("Name of the operating system:"+props. GetProperty("Os.name"));System. out. println("Architecture of the Operating system:"+props. GetProperty("Os.arch"));System. out. println("version of the operating system:"+props. GetProperty("Os.version"));System. out. println("file delimiter:"+props. GetProperty("File.separator")); In UNIX systems is "/"System. out. println("path delimiter:"+props. GetProperty("Path.separator")); In a Unix system is ":"System. out. println("line delimiter:"+props. GetProperty("Line.separator")); In UNIX systems is "/n"System. out. println("User's account name:"+props. GetProperty("User.Name"));System. out. println("User's home directory:"+props. GetProperty("User.home"));System. out. println("User's current working directory:"+props. GetProperty("User.dir"));

3.2 Annex 2: The most basic path conversion

 @Test public  void  Span class= "Hljs-title" >test_getxmlpath () {String path = Thread.CurrentThread (). Getcontextclassloader (). GetResource (). toString (); Path = Path.replace ( "/' ,  ' \ \ \ ' ); ///replace \  Path = path.replace (, ); //Remove file:  Path = path.replace ( "classes\\" , Span class= "hljs-string" "" "); //remove class\  path = path.substring (1 ); //remove the first \, such as \d:\javaweb ...  Path + =  "web. xml" ; System. out . println (path);} 

@Testpublicvoidtest_getXmlPath() {    String path = System.getProperty("user.dir")+"\\src\\file.txt";    System.out.println();    //★将所有的上面得到的路径中"\"转换成"\\"    path = path.replaceAll("\\\\","\\\\\\\\");    System.out.println(path);}

[Java IO] Basics: Reading files