I. Overview

The problem of always entangling the path when reading the configuration file, in fact, all path problems always escape, do not take off several keywords

Relative path, absolute path, classpath (ClassPath)

First introduce these paths first

relative path:

Relative path: As the name suggests, the path is relative, such as the current path is TEST,

If you want to locate the file under Test, you can use a relative path.

For example, there are AAAs under Test,

Then the path relative to TEST is Test / AAA.

Absolute path:

The absolute path is actually a "relative path", but it is relative to the disk (C drive, D disk waiting) or the root directory in Linux.

For example: c: \ users \ 79894 \ desktop \ csdn note

Class path:

This class path is the names of the class file, why is you using a class path in Java?

It is definitely for convenience, how can it be convenient?

For example, I wrote a project, there is a lot of source files in it, and there will be a lot of Class files after the source file is compiled.

You can't let these Java files and Class files together, that's more chaotic.

So the general IDE creates a folder specifically store class file when building a project, also called the output path Output, which stores the same directory store file with the source file directory results.

That problem is coming, talk so much, is there a hair relationship with a class path?

Then let's imagine, if there is no class path, now there is a relative path and absolute path

If you need to locate a file, the absolute path is definitely not, because the project is definitely to be transplanted.

That can only use a relative path, if you use a relative path, the best definitely is better than the root directory of the project, because you can find all the files.

So every time you have to read the file, you must write a relative path of the project, is it troublesome?

So introducing a class path - ClassPath, this path is actually the relative path of the project, but it is written to a file. ClassPath

Then when a Java program is running, just use the relative path, you will find the relative path from this .classpath file.

II. GetResourceceasstream usage

1 Overview

This method is generally used to obtain information about the configuration file.

2. Usage

Two ways:

1.TestClass.class.getResourceAsStream(String path);

2.TestClass.class.getClassLoader.getResourceAsStream(String path);

3.class.getResourceAsStream

If PATH does not bring "/", then find the file from the path of the current class file.

If the PATH belt "/", then it is to find a file from the class path .classpath

4.class.getClassLoader.getResourceAsStream

Can you bring / because this means is to find a file in class path Classpath.

5. ClassPath in Maven

<?xml version="1.0" encoding="UTF-8"?>
<classpath>

	<classpathentry kind="src" output="target/classes" path="src/main/java">
		<attributes>
			<attribute name="optional" value="true"/>
			<attribute name="maven.pomderived" value="true"/>
		</attributes>
	</classpathentry>
	
	<classpathentry excluding="**" kind="src" output="target/classes" path="src/main/resources">
		<attributes>
			<attribute name="maven.pomderived" value="true"/>
		</attributes>
	</classpathentry>
	
	<classpathentry kind="src" output="target/test-classes" path="src/test/java">
		<attributes>
			<attribute name="optional" value="true"/>
			<attribute name="maven.pomderived" value="true"/>
		</attributes>
	</classpathentry>
	
	<classpathentry excluding="**" kind="src" output="target/test-classes" path="src/test/resources">
		<attributes>
			<attribute name="maven.pomderived" value="true"/>
		</attributes>
	</classpathentry>
	
	<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">
		<attributes>
			<attribute name="maven.pomderived" value="true"/>
		</attributes>
	</classpathentry>
	
	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8">
		<attributes>
			<attribute name="maven.pomderived" value="true"/>
		</attributes>
	</classpathentry>
	
	<classpathentry kind="output" path="target/classes"/>
</classpath>

Directory Structure:

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In the Maven project, the configuration file is usually placed in Resources, which is generally copied to Classes and Test-Classes in the Target path.

In classpath, there is a configuration that points to Target / Classes and Target / Test-Classes, then getResourceSstream can find the corresponding file based on this XML file.

III. Test code

package com.tl.test;

import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Properties;

public class TestClassPath {
	public static void main(String[] args) throws Exception {
		// Get file input stream 
//		InputStream is = TestClassPath.class.getClassLoader().getResourceAsStream("test/conf.properties");
		InputStream is = TestClassPath.class.getResourceAsStream("/conf2.properties");
		// Get a conversion stream resolution character encoding problem
		InputStreamReader isr = new InputStreamReader(is);
		/ / Get the Properties object
		Properties properties = new Properties();
		/ / Load resource file to Properties
		properties.load(isr);
		// Close the stream (you can turn it off after loading complete)
		isr.close();
		/ / Get the properties in the configuration file
		String username = properties.getProperty("username");
		System.out.println(username);
		
		
	}
}

Everyone can use this class to test the use of getResourceceasstream