Java中获取当前路径

1. 获取当前路径（绝对路径）

package p01;

import java.io.File;
import java.io.IOException;
import java.net.URL;

public class Hello01 {
    public static void main(String[] args) {
        System.out.println(getCurrentPath1());// D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello\bin
        System.out.println(new Hello01().getCurrentPath2());// D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello\bin\p01
        System.out.println(getCurrentPath3());// D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello
        System.out.println(getCurrentPath4());// file:/D:/eclipseJavaWorkspace/eclipse202006Workspace/Hello/bin/
        System.out.println(getCurrentPath5());// D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello\bin
        System.out.println(getCurrentPath6());// D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello
        System.out.println(getCurrentPath7());// /D:/eclipseJavaWorkspace/eclipse202006Workspace/Hello/bin/

        /* 结果：
D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello\bin
D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello\bin\p01
D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello
file:/D:/eclipseJavaWorkspace/eclipse202006Workspace/Hello/bin/
D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello\bin
D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello
D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello\bin
        */
    }

    // 获取当前类的所在工程路径;
    public static String getCurrentPath1() {
        File f = new File(Hello01.class.getResource("/").getPath());
        return f.getPath();
    }

    // 获取当前类的绝对路径；
    public String getCurrentPath2() {
        File f = new File(this.getClass().getResource("").getPath());
        return f.getPath();
    }

    // 获取当前类的所在工程路径;
    public static String getCurrentPath3() {
        File directory = new File("");// 参数为空
        // getCanonicalPath()返回的就是标准的将符号完全解析的路径
        String courseFile = "";
        try {
            courseFile = directory.getCanonicalPath();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return courseFile;
    }

    // 获取当前类的所在工程路径;
    // file:/D:/eclipseJavaWorkspace/eclipse202006Workspace/Hello/bin/
    public static String getCurrentPath4() {
        URL path = Thread.currentThread().getContextClassLoader().getResource("");
        return path.toString();
    }

    public static String getCurrentPath5() {
        return System.getProperty("java.class.path");
    }

    public static String getCurrentPath6() {
        return System.getProperty("user.dir");
    }

    public static String getCurrentPath7() {
        String path = Thread.currentThread().getContextClassLoader().getResource("").getPath();// /D:/eclipseJavaWorkspace/eclipse202006Workspace/Hello/bin/
        String p = new File(path).getAbsolutePath();// D:\eclipseJavaWorkspace\eclipse202006Workspace\Hello\bin
        return p;
    }

}

 2. 获取资源文件的路径，或读文件

获取src下资源文件编译后的路径（即classes路径）：
String s2 = Thread.currentThread().getContextClassLoader().getResource("").getPath();        //   /D:/eclipseJavaWorkspace/eclipse202006Workspace/Hello/bin/
//String s3 = Thread.currentThread().getContextClassLoader().getResource("/").getPath();// java工程下报错：NullPointerException
String s4 = Thread.currentThread().getContextClassLoader().getResource("test.txt").getPath();//   /D:/eclipseJavaWorkspace/eclipse202006Workspace/Hello/bin/test.txt
或者        类名.class.getClassLoader().getResource("").getPath();
或者        this.class.getClassLoader().getResource("").getPath();

//此方法获得的path，虽然前面多一个“/”，但仍然可以用于构造File
File file2 = new File(s2);
File file4 = new File(s4);
InputStream in = new BufferedInputStream(new FileInputStream(new File(s2)));

//还可以 使用如下，直接返回输入流对象
InputStream resourceAsStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("test.txt");//test.txt在src夹下（即classpath下）
if(null == resourceAsStream) {
	throw new RuntimeException("nullPointer...");
}
else {
	StringBuilder sb = new StringBuilder();
	byte[] buf = new byte[512];
	int len = -1;
	try {
		while((len = resourceAsStream.read(buf))!=-1) {
			sb.append(new String(buf,0,len));
		}
		System.out.println(sb.toString());
	} catch (IOException e) {
		e.printStackTrace();
	}
}

 3. Java中的getResourceAsStream有以下几种：

• 1. Class.getResourceAsStream(String path) ： path 不以’/'开头时默认是从此类所在的包下取资源，以'/'开头则是从ClassPath根下获取。其只是通过path构造一个绝对路径，最终还是由ClassLoader获取资源。
• 2. Class.getClassLoader.getResourceAsStream(String path) ：默认则是从ClassPath根下获取，path不能以’/'开头，最终是由ClassLoader获取资源。
• 3. ServletContext. getResourceAsStream(String path)：默认从WebAPP根目录下取资源，Tomcat下path是否以’/'开头无所谓，当然这和具体的容器实现有关。
• 4. Jsp下的application内置对象就是上面的ServletContext的一种实现。