前文有提到Java的默认ClassLoader有三种，且三种的ClassLoader会加载不同的Java类。

他们加载的类的路径在哪？

是否可以进行设置？

本文做一个初步探讨

全量输出

在不配置任何参数的情况下，执行MainTest.java查看默认路径

MainTest.java内容如下

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import java.net.URL;
import java.net.URLClassLoader;

public class MainTest {
    public static void main(String[] args) {
        System.out.println("BootstrapClassLoader LoadPath: ");

        URL[] urls = sun.misc.Launcher.getBootstrapClassPath().getURLs();
        for(URL url : urls)
            System.out.println(url);
        // System.out.println(System.getProperty("sun.boot.class.path")); 也可以
        System.out.println("----------------------------");
	
        //取得扩展类加载器
        URLClassLoader extClassLoader = (URLClassLoader)ClassLoader.getSystemClassLoader().getParent();

        System.out.println(extClassLoader);
        System.out.println("ExtClassLoader LoadPath: ");

        urls = extClassLoader.getURLs();
        for(URL url : urls)
            System.out.println(url);
		// System.out.println(System.getProperty("java.ext.dirs")); 也可以
        System.out.println("----------------------------");

        //取得应用(系统)类加载器
        URLClassLoader appClassLoader = (URLClassLoader)ClassLoader.getSystemClassLoader();

        System.out.println(appClassLoader);
        System.out.println("AppClassLoader LoadPath: ");

        urls = appClassLoader.getURLs();
        for(URL url : urls)
            System.out.println(url);
		// System.out.println(System.getProperty("java.class.path")); 也可以
        System.out.println("----------------------------");
    }
}

使用最原始的方法运行，结果如下：

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cmd>javac.exe .\MainTest.java
# 有一个warning，删除了，不重要，jdk version 如下
# java version "1.8.0_181"
# Java(TM) SE Runtime Environment (build 1.8.0_181-b13)
# Java HotSpot(TM) 64-Bit Server VM (build 25.181-b13, mixed mode)

# 此时的目录结构
# ./
# ├── MainTest.class
# └── MainTest.java

cmd>java.exe MainTest
# 全量输出如下
BootstrapClassLoader LoadPath:
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/resources.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/rt.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/sunrsasign.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jsse.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jce.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/charsets.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jfr.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/classes
----------------------------
sun.misc.Launcher$ExtClassLoader@15db9742
ExtClassLoader LoadPath:
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/access-bridge-64.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/cldrdata.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/dnsns.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/jaccess.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/jfxrt.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/localedata.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/nashorn.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunec.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunjce_provider.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunmscapi.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunpkcs11.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/zipfs.jar
----------------------------
sun.misc.Launcher$AppClassLoader@73d16e93
AppClassLoader LoadPath:
file:/C:/Users/Dan/Desktop/ppppppp/
----------------------------

Class Loader

Bootstrap Class Loader：加载sun.boot.class.path所指定的路径或jar

默认情况下，可以看到加载的类集中在jre\lib目录和jre\classes目录下。

Extension Class Loader：加载java.ext.dirs所指定的路径或jar。

默认情况下，可以看到加载的类集中在jre\lib\ext目录下。

Application Class Loader加载java.class.path并会搜索应用程序的类路径（包括用户定义的类路径和系统类路径）

默认情况下，最简单的情况，可以看到加载的类只有java命令的执行目录。也就是ClassPath的默认路径，相关知识链接

进阶一点

可以看到三个类加载的默认路径还是挺单一的，所以如果我们想要增加类加载器的加载路径，应该如何做呢？

bootclasspath：对应 Bootstrap CLassLoader。java虚拟机系统参数sun.boot.class.path。 Extensions JAR files：对应 Extention ClassLoader 。java虚拟机系统参数java.ext.dirs。 classpath：对应 AppClassLoader。java虚拟机系统参数java.class.path。

Bootstrap Class Loader

如果要修改或者增加Bootstrap Class Loader的加载路径，三个参数

-Xbootclasspath: 完全取代基本核心的Java class 搜索路径.不常用（慎用）,否则要重新写所有Java核心类
-Xbootclasspath/a: 后缀。在bootclasspath后面添加。常用！！
-Xbootclasspath/p: 前缀。在bootclasspath前面添加。不常用，避免引起不必要的冲突。

-Xbootclasspath/a 示例

省略无关部分，结果如下

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cmd>java.exe -Xbootclasspath/a:.\lib\ MainTest
BootstrapClassLoader LoadPath:
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/resources.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/rt.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/sunrsasign.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jsse.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jce.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/charsets.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jfr.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/classes
file:/C:/Users/Dan/Desktop/ppppppp/lib

可以看到最后一行添加了当前路径下的lib文件夹

-Xbootclasspath/p 示例

省略无关部分，结果如下

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cmd>java.exe -Xbootclasspath/p:.\lib\ MainTest
BootstrapClassLoader LoadPath:
file:/C:/Users/Dan/Desktop/ppppppp/lib
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/resources.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/rt.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/sunrsasign.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jsse.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jce.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/charsets.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jfr.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/classes

可以看到第一行添加了当前路径下的lib文件夹

Tips

可以添加.class文件目录

可以添加.yml、.xml、.properties（或其它配置文件）文件目录

可以添加.jar文件

不可以添加.jar文件所在目录

Extension Class Loader

java -Djava.ext.dirs=...即可添加

-Djava.ext.dirs 示例

需要使用System.out.println(System.getProperty("java.ext.dirs"))来输出，观察变化

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        System.out.println("ExtClassLoader LoadPath: ");
		System.out.println(System.getProperty("java.ext.dirs"));
        System.out.println("----------------------------");

省略无关部分，结果如下

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cmd>java.exe MainTest
# 默认结果 C:\Windows\Sun\Java\lib\ext 不存在该目录
sun.misc.Launcher$ExtClassLoader@15db9742
ExtClassLoader LoadPath:
D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext;C:\Windows\Sun\Java\lib\ext


cmd>java.exe -Djava.ext.dirs=.\test MainTest
# 设置后的结果，只剩下了设置目录
sun.misc.Launcher$ExtClassLoader@15db9742
ExtClassLoader LoadPath:
.\test


cmd>java.exe -Djava.ext.dirs="%JAVA_HOME%jre\lib\ext;.\target" MainTest
# 推荐设置结果，包含了默认结果中的重要部分和自定义部分
sun.misc.Launcher$ExtClassLoader@15db9742
ExtClassLoader LoadPath:
D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext;.\target

对栗子的解释

-Djava.ext.dirs="%JAVA_HOME%jre\lib\ext;.\target"加引号是因为%JAVA_HOME%包含空格。

尽量将java自带的lib\ext目录带上，即%JAVA_HOME%jre\lib\ext。否则，在用其下.jar时，会发生错误。如果确定不需要其下.jar时，则不用加上java自带的lib\ext目录。

缺少java自带的lib\ext目录时，java.security包不能使用（NoSuchAlgorithmException）。

Tips

不可以添加.class文件目录

不可以添加.jar文件

可以添加.jar文件所在目录

推荐将java自带的lib\ext目录带上

Application Class Loader

java -classpath ...
java -cp ...

注：java -cp ... 是 java -classpath ... 的简写

-classpath 示例

省略无关部分，结果如下在这篇文章中也有用到

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cmd>java.exe -cp .\ttttest MainTest
# 因为-cp参数被覆盖，默认有当前路径 . 但是覆盖后只有 .\ttttest ，不在当前路径就找不到字节码文件，所以报错
错误: 找不到或无法加载主类 MainTest

cmd>java.exe -cp .;.\ttttest MainTest
# 多个路径以;符号为分隔，.表示当前路径，添加后报错解除
sun.misc.Launcher$AppClassLoader@73d16e93
AppClassLoader LoadPath:
file:/C:/Users/Dan/Desktop/ppppppp/
file:/C:/Users/Dan/Desktop/ppppppp/ttttest
----------------------------

可以看到最后一行添加了ttttest文件夹

如果参数为.\ttttest;.则结果为

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cmd>java.exe -cp .\ttttest;. MainTest
sun.misc.Launcher$AppClassLoader@73d16e93
AppClassLoader LoadPath:
file:/C:/Users/Dan/Desktop/ppppppp/ttttest
file:/C:/Users/Dan/Desktop/ppppppp/
----------------------------

可以看到第一行添加了ttttest文件夹

Tips

鸡粒推荐！！加入当前文件路径

可以添加.class文件目录

可以添加.jar文件

不可以添加.jar文件所在目录

可以通配符* java -cp target\* test.Test target\*是个特例，可以让java自动搜索其下的.jar文件，并加载。

IDEA 结果一探

将代码放入IDEA进行执行，会发现结果不同

IDEA结果如下

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BootstrapClassLoader LoadPath: 
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/resources.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/rt.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/sunrsasign.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jsse.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jce.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/charsets.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jfr.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/classes
----------------------------
sun.misc.Launcher$ExtClassLoader@3eb07fd3
ExtClassLoader LoadPath: 
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/access-bridge-64.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/cldrdata.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/dnsns.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/jaccess.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/jfxrt.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/localedata.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/nashorn.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunec.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunjce_provider.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunmscapi.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunpkcs11.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/zipfs.jar
----------------------------
sun.misc.Launcher$AppClassLoader@18b4aac2
AppClassLoader LoadPath: 
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/charsets.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/deploy.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/access-bridge-64.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/cldrdata.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/dnsns.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/jaccess.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/jfxrt.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/localedata.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/nashorn.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunec.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunjce_provider.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunmscapi.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/sunpkcs11.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/ext/zipfs.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/javaws.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jce.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jfr.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jfxswt.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/jsse.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/management-agent.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/plugin.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/resources.jar
file:/D:/Program%20Files/Java/jdk1.8.0_181/jre/lib/rt.jar
file:/D:/Users/Dan/Code/Java/Empty/target/classes/
file:/C:/Users/Dan/.m2/repository/org/reflections/reflections/0.9.9/reflections-0.9.9.jar
file:/C:/Users/Dan/.m2/repository/com/google/guava/guava/15.0/guava-15.0.jar
file:/C:/Users/Dan/.m2/repository/com/google/code/findbugs/annotations/2.0.1/annotations-2.0.1.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/resolver/shrinkwrap-resolver-api/2.2.6/shrinkwrap-resolver-api-2.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/resolver/shrinkwrap-resolver-spi/2.2.6/shrinkwrap-resolver-spi-2.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/resolver/shrinkwrap-resolver-api-maven/2.2.6/shrinkwrap-resolver-api-maven-2.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/resolver/shrinkwrap-resolver-spi-maven/2.2.6/shrinkwrap-resolver-spi-maven-2.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/resolver/shrinkwrap-resolver-api-maven-archive/2.2.6/shrinkwrap-resolver-api-maven-archive-2.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/shrinkwrap-api/1.2.6/shrinkwrap-api-1.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/resolver/shrinkwrap-resolver-impl-maven/2.2.6/shrinkwrap-resolver-impl-maven-2.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/eclipse/aether/aether-api/1.0.0.v20140518/aether-api-1.0.0.v20140518.jar
file:/C:/Users/Dan/.m2/repository/org/eclipse/aether/aether-impl/1.0.0.v20140518/aether-impl-1.0.0.v20140518.jar
file:/C:/Users/Dan/.m2/repository/org/eclipse/aether/aether-spi/1.0.0.v20140518/aether-spi-1.0.0.v20140518.jar
file:/C:/Users/Dan/.m2/repository/org/eclipse/aether/aether-util/1.0.0.v20140518/aether-util-1.0.0.v20140518.jar
file:/C:/Users/Dan/.m2/repository/org/eclipse/aether/aether-connector-basic/1.0.0.v20140518/aether-connector-basic-1.0.0.v20140518.jar
file:/C:/Users/Dan/.m2/repository/org/eclipse/aether/aether-transport-wagon/1.0.0.v20140518/aether-transport-wagon-1.0.0.v20140518.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/maven-aether-provider/3.2.5/maven-aether-provider-3.2.5.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/maven-model/3.2.5/maven-model-3.2.5.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/maven-model-builder/3.2.5/maven-model-builder-3.2.5.jar
file:/C:/Users/Dan/.m2/repository/org/codehaus/plexus/plexus-component-annotations/1.5.5/plexus-component-annotations-1.5.5.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/maven-repository-metadata/3.2.5/maven-repository-metadata-3.2.5.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/maven-settings/3.2.5/maven-settings-3.2.5.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/maven-settings-builder/3.2.5/maven-settings-builder-3.2.5.jar
file:/C:/Users/Dan/.m2/repository/org/codehaus/plexus/plexus-interpolation/1.21/plexus-interpolation-1.21.jar
file:/C:/Users/Dan/.m2/repository/org/codehaus/plexus/plexus-utils/3.0.20/plexus-utils-3.0.20.jar
file:/C:/Users/Dan/.m2/repository/org/sonatype/plexus/plexus-sec-dispatcher/1.3/plexus-sec-dispatcher-1.3.jar
file:/C:/Users/Dan/.m2/repository/org/sonatype/plexus/plexus-cipher/1.4/plexus-cipher-1.4.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/wagon/wagon-provider-api/2.6/wagon-provider-api-2.6.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/wagon/wagon-file/2.6/wagon-file-2.6.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/wagon/wagon-http-lightweight/2.6/wagon-http-lightweight-2.6.jar
file:/C:/Users/Dan/.m2/repository/org/apache/maven/wagon/wagon-http-shared/2.6/wagon-http-shared-2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/resolver/shrinkwrap-resolver-impl-maven-archive/2.2.6/shrinkwrap-resolver-impl-maven-archive-2.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/shrinkwrap-impl-base/1.2.6/shrinkwrap-impl-base-1.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/shrinkwrap-spi/1.2.6/shrinkwrap-spi-1.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/shrinkwrap/resolver/shrinkwrap-resolver-spi-maven-archive/2.2.6/shrinkwrap-resolver-spi-maven-archive-2.2.6.jar
file:/C:/Users/Dan/.m2/repository/org/eclipse/sisu/org.eclipse.sisu.plexus/0.3.0.M1/org.eclipse.sisu.plexus-0.3.0.M1.jar
file:/C:/Users/Dan/.m2/repository/org/eclipse/sisu/org.eclipse.sisu.inject/0.3.0.M1/org.eclipse.sisu.inject-0.3.0.M1.jar
file:/C:/Users/Dan/.m2/repository/org/codehaus/plexus/plexus-compiler-javac/2.3/plexus-compiler-javac-2.3.jar
file:/C:/Users/Dan/.m2/repository/org/codehaus/plexus/plexus-compiler-api/2.3/plexus-compiler-api-2.3.jar
file:/C:/Users/Dan/.m2/repository/org/javassist/javassist/3.19.0-GA/javassist-3.19.0-GA.jar
file:/C:/Users/Dan/.m2/repository/com/nqzero/permit-reflect/0.3/permit-reflect-0.3.jar
file:/C:/Users/Dan/.m2/repository/commons-codec/commons-codec/1.9/commons-codec-1.9.jar
file:/C:/Users/Dan/.m2/repository/commons-io/commons-io/2.6/commons-io-2.6.jar
file:/C:/Users/Dan/.m2/repository/org/jenkins-ci/main/remoting/2.55/remoting-2.55.jar
file:/C:/Users/Dan/.m2/repository/org/jenkins-ci/constant-pool-scanner/1.2/constant-pool-scanner-1.2.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/logging/jboss-logging/3.3.0.Final/jboss-logging-3.3.0.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/remoting/jboss-remoting/4.0.19.Final/jboss-remoting-4.0.19.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/xnio/xnio-api/3.3.4.Final/xnio-api-3.3.4.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/jboss-common-core/2.5.0.Final/jboss-common-core-2.5.0.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/xnio/xnio-nio/3.3.4.Final/xnio-nio-3.3.4.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/sasl/jboss-sasl/1.0.5.Final/jboss-sasl-1.0.5.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/remotingjmx/remoting-jmx/2.0.1.Final/remoting-jmx-2.0.1.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/logging/jboss-logging-processor/1.2.0.Final/jboss-logging-processor-1.2.0.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/jdeparser/jdeparser/1.0.0.Final/jdeparser-1.0.0.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/marshalling/jboss-marshalling/1.4.10.Final/jboss-marshalling-1.4.10.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/marshalling/jboss-marshalling-river/1.4.10.Final/jboss-marshalling-river-1.4.10.Final.jar
file:/C:/Users/Dan/.m2/repository/commons-collections/commons-collections/3.1/commons-collections-3.1.jar
file:/C:/Users/Dan/.m2/repository/org/beanshell/bsh/2.0b5/bsh-2.0b5.jar
file:/C:/Users/Dan/.m2/repository/commons-beanutils/commons-beanutils/1.9.2/commons-beanutils-1.9.2.jar
file:/C:/Users/Dan/.m2/repository/commons-logging/commons-logging/1.1.1/commons-logging-1.1.1.jar
file:/C:/Users/Dan/.m2/repository/org/apache/commons/commons-collections4/4.0/commons-collections4-4.0.jar
file:/C:/Users/Dan/.m2/repository/org/codehaus/groovy/groovy/2.3.9/groovy-2.3.9.jar
file:/C:/Users/Dan/.m2/repository/org/springframework/spring-core/4.1.4.RELEASE/spring-core-4.1.4.RELEASE.jar
file:/C:/Users/Dan/.m2/repository/org/springframework/spring-beans/4.1.4.RELEASE/spring-beans-4.1.4.RELEASE.jar
file:/C:/Users/Dan/.m2/repository/org/hibernate/hibernate-core/4.3.11.Final/hibernate-core-4.3.11.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/logging/jboss-logging-annotations/1.2.0.Beta1/jboss-logging-annotations-1.2.0.Beta1.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/spec/javax/transaction/jboss-transaction-api_1.2_spec/1.0.0.Final/jboss-transaction-api_1.2_spec-1.0.0.Final.jar
file:/C:/Users/Dan/.m2/repository/dom4j/dom4j/1.6.1/dom4j-1.6.1.jar
file:/C:/Users/Dan/.m2/repository/xml-apis/xml-apis/1.0.b2/xml-apis-1.0.b2.jar
file:/C:/Users/Dan/.m2/repository/org/hibernate/common/hibernate-commons-annotations/4.0.5.Final/hibernate-commons-annotations-4.0.5.Final.jar
file:/C:/Users/Dan/.m2/repository/org/hibernate/javax/persistence/hibernate-jpa-2.1-api/1.0.0.Final/hibernate-jpa-2.1-api-1.0.0.Final.jar
file:/C:/Users/Dan/.m2/repository/antlr/antlr/2.7.7/antlr-2.7.7.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/jandex/1.1.0.Final/jandex-1.1.0.Final.jar
file:/C:/Users/Dan/.m2/repository/org/springframework/spring-aop/4.1.4.RELEASE/spring-aop-4.1.4.RELEASE.jar
file:/C:/Users/Dan/.m2/repository/aopalliance/aopalliance/1.0/aopalliance-1.0.jar
file:/C:/Users/Dan/.m2/repository/net/sf/json-lib/json-lib/2.4/json-lib-2.4-jdk15.jar
file:/C:/Users/Dan/.m2/repository/commons-lang/commons-lang/2.5/commons-lang-2.5.jar
file:/C:/Users/Dan/.m2/repository/net/sf/ezmorph/ezmorph/1.0.6/ezmorph-1.0.6.jar
file:/C:/Users/Dan/.m2/repository/commons-fileupload/commons-fileupload/1.3/commons-fileupload-1.3.jar
file:/C:/Users/Dan/.m2/repository/org/apache/wicket/wicket-util/6.23.0/wicket-util-6.23.0.jar
file:/C:/Users/Dan/.m2/repository/com/mchange/c3p0/0.9.5.2/c3p0-0.9.5.2.jar
file:/C:/Users/Dan/.m2/repository/com/mchange/mchange-commons-java/0.2.11/mchange-commons-java-0.2.11.jar
file:/C:/Users/Dan/.m2/repository/javax/servlet/javax.servlet-api/3.1.0/javax.servlet-api-3.1.0.jar
file:/C:/Users/Dan/.m2/repository/org/apache/myfaces/core/myfaces-impl/2.2.9/myfaces-impl-2.2.9.jar
file:/C:/Users/Dan/.m2/repository/org/apache/myfaces/core/myfaces-api/2.2.9/myfaces-api-2.2.9.jar
file:/C:/Users/Dan/.m2/repository/org/apache/geronimo/specs/geronimo-atinject_1.0_spec/1.0/geronimo-atinject_1.0_spec-1.0.jar
file:/C:/Users/Dan/.m2/repository/commons-digester/commons-digester/1.8/commons-digester-1.8.jar
file:/C:/Users/Dan/.m2/repository/xalan/xalan/2.7.2/xalan-2.7.2.jar
file:/C:/Users/Dan/.m2/repository/xalan/serializer/2.7.2/serializer-2.7.2.jar
file:/C:/Users/Dan/.m2/repository/rome/rome/1.0/rome-1.0.jar
file:/C:/Users/Dan/.m2/repository/jdom/jdom/1.0/jdom-1.0.jar
file:/C:/Users/Dan/.m2/repository/org/python/jython-standalone/2.5.2/jython-standalone-2.5.2.jar
file:/C:/Users/Dan/.m2/repository/rhino/js/1.7R2/js-1.7R2.jar
file:/C:/Users/Dan/.m2/repository/javassist/javassist/3.12.0.GA/javassist-3.12.0.GA.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/weld/weld-core/1.1.33.Final/weld-core-1.1.33.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/weld/weld-api/1.1.Final/weld-api-1.1.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/weld/weld-spi/1.1.Final/weld-spi-1.1.Final.jar
file:/C:/Users/Dan/.m2/repository/javax/annotation/jsr250-api/1.0/jsr250-api-1.0.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/spec/javax/interceptor/jboss-interceptors-api_1.1_spec/1.0.0.Beta1/jboss-interceptors-api_1.1_spec-1.0.0.Beta1.jar
file:/C:/Users/Dan/.m2/repository/org/slf4j/slf4j-ext/1.7.2/slf4j-ext-1.7.2.jar
file:/C:/Users/Dan/.m2/repository/ch/qos/cal10n/cal10n-api/0.7.7/cal10n-api-0.7.7.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/interceptor/jboss-interceptor-core/2.0.0.Final/jboss-interceptor-core-2.0.0.Final.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/interceptor/jboss-interceptor-spi/2.0.0.Final/jboss-interceptor-spi-2.0.0.Final.jar
file:/C:/Users/Dan/.m2/repository/javax/enterprise/cdi-api/1.0-SP1/cdi-api-1.0-SP1.jar
file:/C:/Users/Dan/.m2/repository/org/jboss/interceptor/jboss-interceptor-api/1.1/jboss-interceptor-api-1.1.jar
file:/C:/Users/Dan/.m2/repository/javax/inject/javax.inject/1/javax.inject-1.jar
file:/C:/Users/Dan/.m2/repository/javax/interceptor/javax.interceptor-api/3.1/javax.interceptor-api-3.1.jar
file:/C:/Users/Dan/.m2/repository/org/slf4j/slf4j-api/1.7.21/slf4j-api-1.7.21.jar
file:/C:/Users/Dan/.m2/repository/org/slf4j/slf4j-jdk14/1.7.21/slf4j-jdk14-1.7.21.jar
file:/C:/Users/Dan/.m2/repository/org/clojure/clojure/1.8.0/clojure-1.8.0.jar
file:/C:/Users/Dan/.m2/repository/com/vaadin/vaadin-server/7.7.14/vaadin-server-7.7.14.jar
file:/C:/Users/Dan/.m2/repository/com/vaadin/vaadin-sass-compiler/0.9.13/vaadin-sass-compiler-0.9.13.jar
file:/C:/Users/Dan/.m2/repository/org/w3c/css/sac/1.3/sac-1.3.jar
file:/C:/Users/Dan/.m2/repository/com/vaadin/external/flute/flute/1.3.0.gg2/flute-1.3.0.gg2.jar
file:/C:/Users/Dan/.m2/repository/com/vaadin/vaadin-shared/7.7.14/vaadin-shared-7.7.14.jar
file:/C:/Users/Dan/.m2/repository/org/jsoup/jsoup/1.8.3/jsoup-1.8.3.jar
file:/C:/Users/Dan/.m2/repository/org/aspectj/aspectjweaver/1.9.5/aspectjweaver-1.9.5.jar
file:/C:/Users/Dan/.m2/repository/org/apache/click/click-nodeps/2.3.0/click-nodeps-2.3.0.jar
file:/C:/Users/Dan/.m2/repository/ognl/ognl/2.6.9/ognl-2.6.9.jar
file:/C:/Users/Dan/.m2/repository/org/apache/velocity/velocity/1.7/velocity-1.7.jar
file:/C:/Users/Dan/.m2/repository/org/mortbay/jasper/apache-el/8.0.27/apache-el-8.0.27.jar
file:/D:/Program%20Files/JetBrains/IntelliJ%20IDEA%202024.2.3/lib/idea_rt.jar
----------------------------

对比图如下：

发现在AppClassLoader LoadPath这一栏增加了巨量的jar文件，这是怎么回事？

原因是因为IDEA的启动语句

1

"D:\Program Files\Java\jdk1.8.0_181\bin\java.exe" "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA 2024.2.3\lib\idea_rt.jar=1928:D:\Program Files\JetBrains\IntelliJ IDEA 2024.2.3\bin" -Dfile.encoding=UTF-8 -classpath "D:\Program Files\Java\jdk1.8.0_181\jre\lib\charsets.jar;......#超级多" com.study.java.MainTest

可以看到，第一个参数是确定启动的java程序全路径，第二个-javaagent参数暂时不做学习

-Dfile.encoding=UTF-8是做了编码统一，最后就是-classpath指定ClassPath 这个参数后面跟了很多包路径

所以最后，IDEA只是根据我们的设置去自动配置好了需要执行的命令，不需要我们去手动配置相关环境

豪用，爱用

Tips

自JDK 1.2以后，JVM采用了委托(delegate)模式来载入class。采用这种设计的原因可以参考： http://java.sun.com/docs/books/tutorial/ext/basics/load.html
ExtClassLoader 和 AppClassLoader在JVM启动后，会在JVM中保存一份，并且在程序运行中无法改变其搜索路径。如果想在运行时从其他搜索路径加载类，就要产生新的类加载器。