update

Author: kimmking

01jvm/out/production/01jvm/README.md

@@ -113,6 +113,36 @@ java -Xmx2g -Xms2g -XX:+UseG1GC -verbose:gc -XX:+PrintGCDateStamps -XX:+PrintGCD
 
 其中 [GCLogAnalysis.java](./GCLogAnalysis.java) 文件也可以从课件资料zip中找到.
 
+## 几个命令用法
+### 1、十六进制方式查看文件
+`hexdump -C Hello.class` 
+输出：`00000000  ca fe ba be 00 00 00 34  00 1c 0a 00 06 00 0e 09`
+
+可以看到magic number： `cafe babe`，
+以及`00 00 00 34`，十六进制34=十进制3*16+4=52，这是jdk8，如果是jdk11则是55，十六进制37.
+
+### 2、Base64方式编码文件
+`base64 Hello.class`
+### 3、显示JVM默认参数
+```
+java -XX:+PrintFlagsFinal -version 
+
+java -XX:+PrintFlagsFinal -version | grep -F " Use" | grep -F "GC "
+
+java -XX:+PrintFlagsFinal -version | grep MaxNewSize
+
+```
+
+### 4、切换不同jdk
+```
+jenv shell 1.8
+jenv shell 11
+```
+显示所有jdk
+```
+jenv versions
+```
+
 ## 更多资料
 
 更多中英文的技术文章和参考资料: <https://github.com/cncounter/translation>

01jvm/subinterface/Mapper.java

@@ -0,0 +1,7 @@
+package subinterface;
+
+public interface Mapper<T> {
+
+    void insert(T t);
+
+}

01jvm/subinterface/User.java

@@ -0,0 +1,17 @@
+package subinterface;
+
+public class User {
+    private int id;
+
+    public User(int id) {
+        this.id = id;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+}

01jvm/subinterface/UserDAO.java

@@ -0,0 +1,9 @@
+package subinterface;
+
+public class UserDAO implements UserMapper {
+
+    @Override
+    public void insert(User user) {
+        System.out.println("Insert user id: " + user.getId());
+    }
+}

01jvm/subinterface/UserMain.java

@@ -0,0 +1,10 @@
+package subinterface;
+
+public class UserMain {
+
+    public static void main(String[] args) {
+        UserDAO dao = new UserDAO();
+        dao.insert(new User(123));
+    }
+
+}

01jvm/subinterface/UserMapper.java

@@ -0,0 +1,7 @@
+package subinterface;
+
+public interface UserMapper extends Mapper<User> {
+
+    @Override
+    void insert(User user);
+}

04fx/java8/src/main/java/io/kimmking/java8/ResourceLoader.java

@@ -0,0 +1,56 @@
+package io.kimmking.java8;
+
+import lombok.SneakyThrows;
+
+import java.io.BufferedReader;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+
+public class ResourceLoader {
+
+    static String file = "conf/a.properties";
+
+    public static void main(String[] args) {
+
+        // testClassLoaderRootPath(); // classloader方式不能加根路径，否则文件路径会直接被替换掉最终成了 /conf/a.properties
+        testClassLoader(); // 从当前的classpath，不管是 文件夹，还是jar里去找 资源
+        testClassRootPath(); // 判断第一个字符是根路径，去掉根，转成 testClassLoader 调用
+        // testClass(); // class 方式必须加根路径，不加根会根据类路径io.kimmking.java8.ResourceLoader 去拼成 io/kimmking/java8/conf/a.properties
+
+
+    }
+
+    private static void testClassLoader() {
+        System.out.println("====> testClassLoader");
+        loadStream(ResourceLoader.class.getClassLoader().getResourceAsStream(file));
+    }
+
+    private static void testClassLoaderRootPath() {
+        System.out.println("====> testClassLoader");
+        loadStream(ResourceLoader.class.getClassLoader().getResourceAsStream("/"+file));
+    }
+
+    private static void testClass() {
+        System.out.println("====> testClass");
+        loadStream(ResourceLoader.class.getResourceAsStream(file));
+    }
+
+    private static void testClassRootPath() {
+        System.out.println("====> testClassRootPath");
+        loadStream(ResourceLoader.class.getResourceAsStream("/"+file));
+    }
+
+    @SneakyThrows
+    private static void loadStream(InputStream in) {
+        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
+        StringBuffer buffer = new StringBuffer();
+        String line = null;
+        while ((line = reader.readLine()) != null) {
+            buffer.append(line);
+        }
+        System.out.println(buffer.toString());
+        reader.close();
+        in.close();
+    }
+
+}

04fx/java8/src/main/resources/conf/a.properties

@@ -0,0 +1,2 @@
+a=1
+b=2