Merge remote-tracking branch 'origin/master'

Author: coderzyj

java-classloader/java-classloader.iml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>

java-classloader/src/com/zyj/test/Demo01.java

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+package com.zyj.test;
+
+/**
+ * 版权声明：CopyRight (c) 2018 ucarinc. All Rights Reserved.
+ *
+ * @author : 张勇杰
+ * @date : 2018/12/3 16:16
+ * @Version : v1.0
+ * @description
+ **/
+public class Demo01 {
+    public static void main(String[] args) {
+        System.out.println(ClassLoader.getSystemClassLoader());
+        System.out.println(ClassLoader.getSystemClassLoader().getParent());
+        System.out.println(ClassLoader.getSystemClassLoader().getParent().getParent());
+
+        System.out.println(System.getProperty("java.class" + ".path"));
+        String a = "zyj";
+        System.out.println(a.getClass().getClassLoader());
+
+    }
+}

java-classloader/src/com/zyj/test/Demo02.java

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+package com.zyj.test;
+
+/**
+ * 版权声明：CopyRight (c) 2018 ucarinc. All Rights Reserved.
+ *
+ * @author : 张勇杰
+ * @date : 2018/12/6 15:08
+ * @Version : v1.0
+ * @description
+ **/
+public class Demo02 {
+    public static void main(String[] args) throws ClassNotFoundException {
+        FileSystemClassLoader loader = new FileSystemClassLoader("d:/myjava");
+        FileSystemClassLoader loader1 = new FileSystemClassLoader("d:/myjava");
+        Class<?> c = loader.loadClass("com.zyj.test.HelloWorld");
+        Class<?> c1 = loader.loadClass("com.zyj.test.HelloWorld");
+        Class<?> c2 = loader1.loadClass("com.zyj.test.HelloWorld");
+        Class c3 = loader.loadClass("java.lang.String");
+        System.out.println(c.hashCode());
+        System.out.println(c1.hashCode());
+        System.out.println(c2.hashCode());
+        System.out.println(c3.hashCode());
+        //JVM认为被同一个加载器加载的同一个类是相同的类
+    }
+}

java-classloader/src/com/zyj/test/FileSystemClassLoader.java

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+package com.zyj.test;
+
+import java.io.*;
+
+/**
+ * 版权声明：CopyRight (c) 2018 ucarinc. All Rights Reserved.
+ *
+ * @author : 张勇杰
+ * @date : 2018/12/6 14:47
+ * @Version : v1.0
+ * @description
+ **/
+public class FileSystemClassLoader extends ClassLoader {
+    //d:/myjava/com/zyj/test/User.class  -->com.zyj.test.User
+    private String rootDir;
+
+    public FileSystemClassLoader(String rootDir){
+        this.rootDir = rootDir;
+    }
+
+    @Override
+    protected Class<?> findClass(String name) throws ClassNotFoundException {
+        Class<?> c = findLoadedClass(name);
+
+        //应该先查询有没有加载过这个类，如果已经加载，则返回已经加载好的类。如果没有，则加载新的类
+        if(c != null){
+            return c;
+        }else{
+            ClassLoader parent = this.getParent();
+            System.out.println(parent);
+            //委派给父类加载
+            try {
+                c = parent.loadClass(name);
+            }catch (Exception e){
+
+            }
+
+            if(c != null){
+                return c;
+            }else{
+                byte[] classData = getClassData(name);
+                if(classData == null){
+                    throw new ClassNotFoundException();
+                }else{
+                    c = defineClass(name,classData,0,classData.length);
+                }
+            }
+        }
+        return c;
+    }
+
+    private byte[] getClassData(String className){
+        String path = rootDir + "/"+className.replace(".","/")+".class";
+
+        //IOUtils,可以使用他将流中的数据转成字节数组
+        InputStream is = null;
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        try {
+            is = new FileInputStream(path);
+            byte[] buffer = new byte[1024];
+            int temp = 0;
+            while((temp = is.read(buffer))!= -1){
+                baos.write(buffer,0,temp);
+            }
+            return baos.toByteArray();
+        } catch (Exception e) {
+            e.printStackTrace();
+            return null;
+        }finally {
+            if(is != null){
+                try {
+                    is.close();
+                } catch (IOException e) {
+                    e.printStackTrace();
+                }
+            }
+            if (baos != null) {
+
+                try {
+                    baos.close();
+                } catch (IOException e) {
+                    e.printStackTrace();
+                }
+            }
+        }
+    }
+}

java-classloader/src/com/zyj/test/Test02.java

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+package com.zyj.test;
+
+/**
+ * 版权声明：CopyRight (c) 2018 ucarinc. All Rights Reserved.
+ *
+ * @author : 张勇杰
+ * @date : 2018/12/6 15:52
+ * @Version : v1.0
+ * @description
+ **/
+public class Test02 extends Test1 {
+    @Override
+    protected String test01() throws Exception {
+        return "我才是返回值";
+    }
+
+    public static void main(String[] args) {
+        Test02 test02 = new Test02();
+        try {
+            System.out.println(test02.test02());
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+}

java-classloader/src/com/zyj/test/Test1.java

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+package com.zyj.test;
+
+/**
+ * 版权声明：CopyRight (c) 2018 ucarinc. All Rights Reserved.
+ *
+ * @author : 张勇杰
+ * @date : 2018/12/6 15:51
+ * @Version : v1.0
+ * @description
+ **/
+public abstract class Test1 {
+    protected String test01() throws Exception {
+        throw new Exception("666");
+    }
+    protected String test02() throws Exception{
+        String c = test01();
+        return c;
+    }
+}