classloader 热部署

classloader 热部署
这两天一直在学习一些classloader的相关知识，看了一些文章，了解到classloader的作用之一就是实现热部署功能。于是就看了一个网络上的一个例子，然后自己实现了一个应用。虽然作出来了，但是说实话：不满意。因为在这个例子当中，只要热部署一次，就要重新new一个classloader，这样会引发什么问题我也不清楚，并且，classloader究竟实现了什么，以及一些底层的东西我还不是很了解，还要继续研究，目前的版本就是一个中间版本。以后还要优化，或者在我读完tomcat的classloader之后我在去仿照着写一个。

1,使用CLass.forName()可以动态的得到一个.class的类。

2，Thread.currentThread().getContextClassLoader())得到当前的classloader。然后就可以得到classpath下面任何包中的类

好了，下面介绍这个工程的构思、以及实现方式，设计思想:首先来说：这个工程至少需要是需要2个线程，一个是类似tomcat的服务线程，另外一个就是检测线程，检测变化，重新加载Class对象。我猜tomcat是采取了检测类，检测加载了的类文件变化。我没有那么实现，因为这种实现方式相对复杂，并且我的想集中解决热部署问题，而不是如何实现监控文件，所以我就采取了相对简单的方式：socket通知方式。也就是，在我重新编译一个class之后，利用socket通知检测线程，监测监测在监测到socket命令之后会自动的加载。
Java代码
1. Java代码
2. package com.cxz.classloader;
4. import com.cxz.jiangyou.Say;
6. import java.io.ByteArrayOutputStream;
7. import java.io.File;
8. import java.io.FileInputStream;
9. import java.io.IOException;
11. /**
12. * This classloader is like a template
13. * which includes pre-loadClass and after-loadClass
14. * @author Bernard
15. *
16. */
17. public class ComplexClassLoader extends ClassLoader {
19. public ComplexClassLoader() {
20. }
22. public ComplexClassLoader(String defaultTargetDir) {
23. this.defaultTargetDir = defaultTargetDir;
24. }
26. private String defaultTargetDir = "D://hotdeploys//";
28. public Class<?> findClass(String className) throws ClassNotFoundException {
29. byte[] classBytes = null;
30. try {
31. classBytes = loadByteCode(className);
32. } catch (IOException e) {
33. // TODO Auto-generated catch block
34. e.printStackTrace();
35. }
36. return super.defineClass(className, classBytes, 0, classBytes.length);
37. }
39. private byte[] loadByteCode(String className) throws IOException {
40. int ch = 0;
41. className = className.replaceAll("//.", "////") + ".class";
42. //The two slashes represent for meaning changing
43. File file = new File(defaultTargetDir + className);
44. FileInputStream in = null;
45. in = new FileInputStream(file);
46. ByteArrayOutputStream buffer = new ByteArrayOutputStream();
47. while ((ch = in.read()) != -1) {
48. buffer.write(ch);
49. }
50. in.close();
51. return buffer.toByteArray();
52. }
54. public String getDefaultTargetDir() {
55. return defaultTargetDir;
56. }
58. public void setDefaultTargetDir(String defaultTargetDir) {
59. this.defaultTargetDir = defaultTargetDir;
60. }
61. }
63. package com.cxz.classloader;
65. import com.cxz.jiangyou.Say;
67. import java.io.ByteArrayOutputStream;
68. import java.io.File;
69. import java.io.FileInputStream;
70. import java.io.IOException;
72. /**
73. * This classloader is like a template
74. * which includes pre-loadClass and after-loadClass
75. * @author Bernard
76. *
77. */
78. public class ComplexClassLoader extends ClassLoader {
80. public ComplexClassLoader() {
81. }
83. public ComplexClassLoader(String defaultTargetDir) {
84. this.defaultTargetDir = defaultTargetDir;
85. }
87. private String defaultTargetDir = "D://hotdeploys//";
89. public Class<?> findClass(String className) throws ClassNotFoundException {
90. byte[] classBytes = null;
91. try {
92. classBytes = loadByteCode(className);
93. } catch (IOException e) {
94. // TODO Auto-generated catch block
95. e.printStackTrace();
96. }
97. return super.defineClass(className, classBytes, 0, classBytes.length);
98. }
100. private byte[] loadByteCode(String className) throws IOException {
101. int ch = 0;
102. className = className.replaceAll("//.", "////") + ".class";
103. //The two slashes represent for meaning changing
104. File file = new File(defaultTargetDir + className);
105. FileInputStream in = null;
106. in = new FileInputStream(file);
107. ByteArrayOutputStream buffer = new ByteArrayOutputStream();
108. while ((ch = in.read()) != -1) {
109. buffer.write(ch);
110. }
111. in.close();
112. return buffer.toByteArray();
113. }
115. public String getDefaultTargetDir() {
116. return defaultTargetDir;
117. }
119. public void setDefaultTargetDir(String defaultTargetDir) {
120. this.defaultTargetDir = defaultTargetDir;
121. }
122. }
```
Java代码 
package com.cxz.classloader;   
  
import com.cxz.jiangyou.Say;   
  
import java.io.ByteArrayOutputStream;   
import java.io.File;   
import java.io.FileInputStream;   
import java.io.IOException;   
  
/**  
 * This classloader is like a template  
 * which includes pre-loadClass and after-loadClass  
 * @author Bernard  
 *  
 */  
public class ComplexClassLoader extends ClassLoader {   
  
    public ComplexClassLoader() {   
    }   
  
    public ComplexClassLoader(String defaultTargetDir) {   
        this.defaultTargetDir = defaultTargetDir;   
    }   
  
    private String defaultTargetDir = "D://hotdeploys//";   
  
    public Class<?> findClass(String className) throws ClassNotFoundException {   
        byte[] classBytes = null;   
        try {   
            classBytes = loadByteCode(className);   
        } catch (IOException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        }   
        return super.defineClass(className, classBytes, 0, classBytes.length);   
    }   
  
    private byte[] loadByteCode(String className) throws IOException {   
        int ch = 0;   
        className = className.replaceAll("//.", "////") + ".class";   
        //The two slashes represent for meaning changing   
        File file = new File(defaultTargetDir + className);   
        FileInputStream in = null;   
        in = new FileInputStream(file);   
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();   
        while ((ch = in.read()) != -1) {   
            buffer.write(ch);   
        }   
        in.close();   
        return buffer.toByteArray();   
    }   
  
    public String getDefaultTargetDir() {   
        return defaultTargetDir;   
    }   
  
    public void setDefaultTargetDir(String defaultTargetDir) {   
        this.defaultTargetDir = defaultTargetDir;   
    }      
}  

package com.cxz.classloader;

import com.cxz.jiangyou.Say;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

/**
 * This classloader is like a template
 * which includes pre-loadClass and after-loadClass
 * @author Bernard
 *
 */
public class ComplexClassLoader extends ClassLoader {

	public ComplexClassLoader() {
	}

	public ComplexClassLoader(String defaultTargetDir) {
		this.defaultTargetDir = defaultTargetDir;
	}

	private String defaultTargetDir = "D://hotdeploys//";

	public Class<?> findClass(String className) throws ClassNotFoundException {
		byte[] classBytes = null;
		try {
			classBytes = loadByteCode(className);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.defineClass(className, classBytes, 0, classBytes.length);
	}

	private byte[] loadByteCode(String className) throws IOException {
		int ch = 0;
		className = className.replaceAll("//.", "////") + ".class";
		//The two slashes represent for meaning changing
		File file = new File(defaultTargetDir + className);
		FileInputStream in = null;
		in = new FileInputStream(file);
		ByteArrayOutputStream buffer = new ByteArrayOutputStream();
		while ((ch = in.read()) != -1) {
			buffer.write(ch);
		}
		in.close();
		return buffer.toByteArray();
	}

	public String getDefaultTargetDir() {
		return defaultTargetDir;
	}

	public void setDefaultTargetDir(String defaultTargetDir) {
		this.defaultTargetDir = defaultTargetDir;
	}	
}
```
该类会自动加载d:/hotdeploys下的类文件．

下面这个就是测试类
Java代码
Java代码
1. package com.cxz.classloader;
3. import java.io.IOException;
4. import java.net.ServerSocket;
5. import java.net.Socket;
7. import com.cxz.jiangyou.Say;
9. public class MultiThreadTest implements Runnable {
11. private static final int portNum = 9090;
13. private static final int sleepCycle = 3000;
15. private Say sayer = null;
17. private ComplexClassLoader loader = new ComplexClassLoader();
19. private String delpoyee = "com.cxz.jiangyou.Sample";
21. public MultiThreadTest() {
22. hotDeploy(delpoyee);
23. }
25. public void startService() {
26. while (true) {
27. synchronized (sayer) {
28. sayer.say();
29. }
30. try {
31. Thread.sleep(sleepCycle);
32. } catch (InterruptedException e) {
33. // TODO Auto-generated catch block
34. e.printStackTrace();
35. }
36. }
37. }
39. public void hotDeploy(String name) {
40. try {
41. if (sayer != null) {
42. synchronized (sayer) {
43. loader = new ComplexClassLoader();
44. sayer = (Say) loader.loadClass(name).newInstance();
45. }
46. System.out.println("-------------->Hot deployment finished!");
47. } else {
48. sayer = (Say) loader.loadClass(name).newInstance();
49. System.out.println("-------------->Initialization finished!");
50. }
52. } catch (InstantiationException e) {
53. // TODO Auto-generated catch block
54. e.printStackTrace();
55. } catch (IllegalAccessException e) {
56. // TODO Auto-generated catch block
57. e.printStackTrace();
58. } catch (ClassNotFoundException e) {
59. // TODO Auto-generated catch block
60. e.printStackTrace();
61. }
62. }
64. @Override
65. public void run() {
66. ServerSocket server = null;
67. Socket socket = null;
68. try {
69. server = new ServerSocket(portNum);
70. while (true) {
71. socket = server.accept();
72. socket.close();
73. hotDeploy(delpoyee);
74. }
75. } catch (IOException e) {
76. // TODO Auto-generated catch block
77. e.printStackTrace();
78. }
79. }
81. public static void main(String[] args) {
82. // new MultiThreadTest().startService();
83. // new MultiThreadTest().run();
84. MultiThreadTest test = new MultiThreadTest();
85. Thread thread = new Thread(test);
86. thread.start();
87. try {
88. thread.sleep(sleepCycle);
89. //Waiting for the deployment Thread deploy the say obj.
90. } catch (InterruptedException e) {
91. // TODO Auto-generated catch block
92. e.printStackTrace();
93. }
94. test.startService();
95. }
97. }
99. package com.cxz.classloader;
101. import java.io.IOException;
102. import java.net.ServerSocket;
103. import java.net.Socket;
105. import com.cxz.jiangyou.Say;
107. public class MultiThreadTest implements Runnable {
109. private static final int portNum = 9090;
111. private static final int sleepCycle = 3000;
113. private Say sayer = null;
115. private ComplexClassLoader loader = new ComplexClassLoader();
117. private String delpoyee = "com.cxz.jiangyou.Sample";
119. public MultiThreadTest() {
120. hotDeploy(delpoyee);
121. }
123. public void startService() {
124. while (true) {
125. synchronized (sayer) {
126. sayer.say();
127. }
128. try {
129. Thread.sleep(sleepCycle);
130. } catch (InterruptedException e) {
131. // TODO Auto-generated catch block
132. e.printStackTrace();
133. }
134. }
135. }
137. public void hotDeploy(String name) {
138. try {
139. if (sayer != null) {
140. synchronized (sayer) {
141. loader = new ComplexClassLoader();
142. sayer = (Say) loader.loadClass(name).newInstance();
143. }
144. System.out.println("-------------->Hot deployment finished!");
145. } else {
146. sayer = (Say) loader.loadClass(name).newInstance();
147. System.out.println("-------------->Initialization finished!");
148. }
150. } catch (InstantiationException e) {
151. // TODO Auto-generated catch block
152. e.printStackTrace();
153. } catch (IllegalAccessException e) {
154. // TODO Auto-generated catch block
155. e.printStackTrace();
156. } catch (ClassNotFoundException e) {
157. // TODO Auto-generated catch block
158. e.printStackTrace();
159. }
160. }
162. @Override
163. public void run() {
164. ServerSocket server = null;
165. Socket socket = null;
166. try {
167. server = new ServerSocket(portNum);
168. while (true) {
169. socket = server.accept();
170. socket.close();
171. hotDeploy(delpoyee);
172. }
173. } catch (IOException e) {
174. // TODO Auto-generated catch block
175. e.printStackTrace();
176. }
177. }
179. public static void main(String[] args) {
180. // new MultiThreadTest().startService();
181. // new MultiThreadTest().run();
182. MultiThreadTest test = new MultiThreadTest();
183. Thread thread = new Thread(test);
184. thread.start();
185. try {
186. thread.sleep(sleepCycle);
187. //Waiting for the deployment Thread deploy the say obj.
188. } catch (InterruptedException e) {
189. // TODO Auto-generated catch block
190. e.printStackTrace();
191. }
192. test.startService();
193. }
195. }
```
package com.cxz.classloader;   
  
import java.io.IOException;   
import java.net.ServerSocket;   
import java.net.Socket;   
  
import com.cxz.jiangyou.Say;   
  
public class MultiThreadTest implements Runnable {   
  
    private static final int portNum = 9090;   
  
    private static final int sleepCycle = 3000;   
  
    private Say sayer = null;   
  
    private ComplexClassLoader loader = new ComplexClassLoader();   
  
    private String delpoyee = "com.cxz.jiangyou.Sample";   
  
    public MultiThreadTest() {   
        hotDeploy(delpoyee);   
    }   
  
    public void startService() {   
        while (true) {   
            synchronized (sayer) {   
                sayer.say();   
            }   
            try {   
                Thread.sleep(sleepCycle);   
            } catch (InterruptedException e) {   
                // TODO Auto-generated catch block   
                e.printStackTrace();   
            }   
        }   
    }   
  
    public void hotDeploy(String name) {   
        try {   
            if (sayer != null) {   
                synchronized (sayer) {   
                    loader = new ComplexClassLoader();   
                    sayer = (Say) loader.loadClass(name).newInstance();   
                }   
                System.out.println("-------------->Hot deployment finished!");   
            } else {   
                sayer = (Say) loader.loadClass(name).newInstance();   
                System.out.println("-------------->Initialization finished!");   
            }   
  
        } catch (InstantiationException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        } catch (IllegalAccessException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        } catch (ClassNotFoundException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        }   
    }   
  
    @Override  
    public void run() {   
        ServerSocket server = null;   
        Socket socket = null;   
        try {   
            server = new ServerSocket(portNum);   
            while (true) {   
                socket = server.accept();   
                socket.close();   
                hotDeploy(delpoyee);   
            }   
        } catch (IOException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        }   
    }   
  
    public static void main(String[] args) {   
        // new MultiThreadTest().startService();   
        // new MultiThreadTest().run();   
        MultiThreadTest test = new MultiThreadTest();   
        Thread thread = new Thread(test);   
        thread.start();   
        try {   
            thread.sleep(sleepCycle);   
            //Waiting for the deployment Thread deploy the say obj.   
        } catch (InterruptedException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        }   
        test.startService();   
    }   
  
}  

package com.cxz.classloader;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

import com.cxz.jiangyou.Say;

public class MultiThreadTest implements Runnable {

	private static final int portNum = 9090;

	private static final int sleepCycle = 3000;

	private Say sayer = null;

	private ComplexClassLoader loader = new ComplexClassLoader();

	private String delpoyee = "com.cxz.jiangyou.Sample";

	public MultiThreadTest() {
		hotDeploy(delpoyee);
	}

	public void startService() {
		while (true) {
			synchronized (sayer) {
				sayer.say();
			}
			try {
				Thread.sleep(sleepCycle);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	public void hotDeploy(String name) {
		try {
			if (sayer != null) {
				synchronized (sayer) {
					loader = new ComplexClassLoader();
					sayer = (Say) loader.loadClass(name).newInstance();
				}
				System.out.println("-------------->Hot deployment finished!");
			} else {
				sayer = (Say) loader.loadClass(name).newInstance();
				System.out.println("-------------->Initialization finished!");
			}

		} catch (InstantiationException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	@Override
	public void run() {
		ServerSocket server = null;
		Socket socket = null;
		try {
			server = new ServerSocket(portNum);
			while (true) {
				socket = server.accept();
				socket.close();
				hotDeploy(delpoyee);
			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public static void main(String[] args) {
		// new MultiThreadTest().startService();
		// new MultiThreadTest().run();
		MultiThreadTest test = new MultiThreadTest();
		Thread thread = new Thread(test);
		thread.start();
		try {
			thread.sleep(sleepCycle);
			//Waiting for the deployment Thread deploy the say obj.
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		test.startService();
	}

}
```
main线程主要是服务线程,通过调用startService()不停的通过system.out来打印。支线程负责监听端口(9090)，当有连接信号后就重新加载类。
服务接口很简单，如下
Java代码
1. Java代码
2. package com.cxz.jiangyou;
3. public interface Say{
4. public void say();
5. }
7. package com.cxz.jiangyou;
8. public interface Say{
9. public void say();
10. }
```
Java代码 
package com.cxz.jiangyou;   
public interface Say{   
    public void say();   
}  

package com.cxz.jiangyou;
public interface Say{
	public void say();
}
```
总结：所有的customerClassLoader都要加载与之相关的类(比如：父类、包含的类)。如果你需要override loadclass(string, boolean)绕过findLoadedClass()检测，只能引发java.lang.LinkageError：duplicate class definition for name: "com/cxz/jiangyou/Sample"因此，比较通用的重新加载方式应该就是new一个用户定义的classloader
相关阅读:
idea打包jar的多种方式，用IDEA自带的打包形式，用IDEA自带的打包形式用Maven插件maven-shade-plugin打包，用Maven插件maven-assembly-plugin打包
 SSH Secure Shell 无法登录：server responded "algorithm negotiation failed”
redis.clients.jedis.HostAndPort
spring boot jar 进程自动停止，自动终止，不能后台持续运行
 剑指Offer_46_孩子们的游戏(圆圈中最后剩下的数)
剑指Offer_45_扑克牌顺子
 剑指Offer_44_翻转单词顺序列
 剑指Offer_43_左旋转字符串
 剑指Offer_42_和为S的两个数字
 剑指Offer_41_和为S的连续正数序列
原文地址：https://www.cnblogs.com/liaomin416100569/p/9331833.html

最新文章
11.3
11.2
11.1 周总结
 10.30 异常处理
 10.29
11.24 form
11.23 Jquery
11.20 JavaScript 变量
 11.19 JavaScript注意事项
 11.18 JavaScript代码练习