使用动态代理方法实现Method hook

本文来自csdn:
http://topic.csdn.net/u/20071030/08/fa2e15dd-1abe-46dc-b76e-9fe2de4e7381.html

问题描述:有这样一个需求，有一个Hashtable存储着一些东西，而且已经序列化到了硬盘上，假如这个Hashtable发生了变化，就将这个新的Hashtable重新序列化到硬盘上，前提是并不知道哪些方法会改变这个Hashtable，这该怎么实现呢？


bao110908[火龙果]:最嘉的答案.

 

 

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Hashtable;
import java.util.Map;

public class HashtableProxyTest {

    public static void main(String[] args) {
        Map<String, String> table = new Hashtable<String, String>();
        HashtableHandler handler = new HashtableHandler();
        table = handler.bind(table);
        
        table.put("abc", "abc");
        Map t1 = WriteFile.readFile();
        System.out.println(t1.size());
        
        m(table);
        t1 = WriteFile.readFile();
        System.out.println(t1.size());
        
        String abc = table.get("abc");        
        t1 = WriteFile.readFile();
        System.out.println(t1.size());
        System.out.println(abc);
        
        table.remove("abc");
        t1 = WriteFile.readFile();
        System.out.println(t1.size());
        
        table.clear();
        t1 = WriteFile.readFile();
        System.out.println(t1.size());
    }   
    
    public static void m(Map<String, String> map) {
        map.put("123", "123");
    }
}

class WriteFile {
    private static File file = new File("Hashtable.obj");
    public static void writeFile(Map<String, String> map) {
        try {
            ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file));
            out.writeObject(map);
            out.close();
        } catch (FileNotFoundException e) {            
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    @SuppressWarnings("unchecked")
    public static Map<String, String> readFile() {
        Map map = null;
        try {
            ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
            map = (Map<String, String>)in.readObject();
            in.close();            
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return map;
    }
}

class HashtableHandler implements InvocationHandler {
    private Map<String, String> table = null;
    
    @SuppressWarnings("unchecked")
    public Map<String, String> bind(Map<String, String> map) {
        table = map;
        Map<String, String> mapProxy = (Map<String, String>)Proxy.newProxyInstance(
                table.getClass().getClassLoader(),
                table.getClass().getInterfaces(),
                this                
            );
        return mapProxy;        
    }
    
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        Object obj = null;        
        // 调用原有的方法
         obj = method.invoke(table, args);        
        String name = method.getName();
        String changeMethod = "(clear)|(put)|(putAll)|(remove)";
        // 当调用的方法为更改 map 中值的方法时，写入文件中
         if(name.matches(changeMethod)) {
            WriteFile.writeFile(table);
        }
        return obj;
    }
}

  

 

 

问题描述: 构造连接池。

来源:http://blog.csdn.net/Coolongxp/archive/2005/04/28/366107.aspx

 

实现了InvocationHandler接口的

Object invoke(Object proxy, Method method, Object[] args)

Proxy 代理类

Method 调用的方法

Args 调用方法的参数

的方法的类可以作为InvocationHandler类的参数来构建Proxy类的实例

static Object newProxyInstance(ClassLoader loader, Class[] interfaces, InvocationHandler h)

loader - the class loader to define the proxy class in

interfaces - the list of interfaces for the proxy class to implement

h - the invocation handler to dispatch method invocations

 

 

ConnectionWrapper(Connection con) {

    Class[] interfaces = {

        java.sql.Connection.class};

    this.connection = (Connection) Proxy.newProxyInstance(

        con.getClass().getClassLoader(),

        interfaces, this);

    m_originConnection = con;

  }

 

public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {

    Object obj = null;

    if (CLOSE_METHOD_NAME.equals(m.getName())) {

      DBConnectionPool.pushConnectionBackToPool(this);

    }

    else {

      obj = m.invoke(m_originConnection, args);

    }

    if (DEBUG) {

        System.out.println(m.getName()+"is invoke!");

    }

    lastAccessTime = System.currentTimeMillis();

    return obj;

  }

  

 

 

 

 

 

作用说明：

当调用被代理的类（Connection）的实例的方法时系统将转到包含代理类（Proxy）的InvocationHandler的invoke方法中去执行相应代码。

这样就可以在不修改代码的前提下为已经存在的类来添加新的功能。

如：（全部代码参看DBConnectionPool.java）

import java.sql.*;
import java.lang.reflect.*;
import java.util.*;
import java.io.*;

public class DBConnectionPool {
  private static LinkedList m_notUsedConnection = new LinkedList();
  private static HashSet m_usedUsedConnection = new HashSet();
  private static String m_url = "";
  private static String m_user = "";
  private static String m_password = "";
  static final boolean DEBUG = true;
  static private long m_lastClearClosedConnection = System.currentTimeMillis();
  public static long CHECK_CLOSED_CONNECTION_TIME = 4 * 60 * 60 * 1000; //4 hours

  static {
    initDriver();
  }

  private DBConnectionPool() {
  }

  private static void initDriver() {
    Driver driver = null;
//load mysql driver
    try {
      driver = (Driver) Class.forName(
          "com.microsoft.jdbc.sqlserver.SQLServerDriver").newInstance();
      installDriver(driver);
    }
    catch (Exception e) {
    }

//load postgresql driver
    try {
      driver = (Driver) Class.forName("org.postgresql.Driver").newInstance();
      installDriver(driver);
    }
    catch (Exception e) {
    }
  }

  public static void installDriver(Driver driver) {
    try {
      DriverManager.registerDriver(driver);
    }
    catch (Exception e) {
     e.printStackTrace();
    }
  }

  public static synchronized Connection getConnection() {
    clearClosedConnection();
    while (m_notUsedConnection.size() > 0) {
      try {
        ConnectionWrapper wrapper = (ConnectionWrapper) m_notUsedConnection.
            removeFirst();
        if (wrapper.connection.isClosed()) {
          continue;
        }
        m_usedUsedConnection.add(wrapper);
        if (DEBUG) {
          wrapper.debugInfo = new Throwable("Connection initial statement");
        }
        return wrapper.connection;
      }
      catch (Exception e) {
      }
    }
    int newCount = getIncreasingConnectionCount();
    LinkedList list = new LinkedList();
    ConnectionWrapper wrapper = null;
    for (int i = 0; i < newCount; i++) {
      wrapper = getNewConnection();
      if (wrapper != null) {
        list.add(wrapper);
      }
    }
    if (list.size() == 0) {
      return null;
    }
    wrapper = (ConnectionWrapper) list.removeFirst();
    m_usedUsedConnection.add(wrapper);

    m_notUsedConnection.addAll(list);
    list.clear();

    return wrapper.connection;
  }

  private static ConnectionWrapper getNewConnection() {
    try {
      Connection con = DriverManager.getConnection(m_url, m_user, m_password);
      ConnectionWrapper wrapper = new ConnectionWrapper(con);
      return wrapper;
    }
    catch (Exception e) {
      e.printStackTrace();
    }
    return null;
  }

  static synchronized void pushConnectionBackToPool(ConnectionWrapper con) {
    boolean exist = m_usedUsedConnection.remove(con);
    if (exist) {
      m_notUsedConnection.addLast(con);
    }
  }

  public static int close() {
    int count = 0;
    if(DEBUG){
     System.out.println("it is DBConnection's close()");
    }
    Iterator iterator = m_notUsedConnection.iterator();
    while (iterator.hasNext()) {
      try {
        ( (ConnectionWrapper) iterator.next()).close();
        count++;
      }
      catch (Exception e) {
      }
    }
    m_notUsedConnection.clear();

    iterator = m_usedUsedConnection.iterator();
    while (iterator.hasNext()) {
      try {
        ConnectionWrapper wrapper = (ConnectionWrapper) iterator.next();
        wrapper.close();
        if (DEBUG) {
          wrapper.debugInfo.printStackTrace();
        }
        count++;
      }
      catch (Exception e) {
      }
    }
    m_usedUsedConnection.clear();

    return count;
  }

  private static void clearClosedConnection() {
    long time = System.currentTimeMillis();
//sometimes user change system time,just return
    if (time < m_lastClearClosedConnection) {
      time = m_lastClearClosedConnection;
      return;
    }
//no need check very often
    if (time - m_lastClearClosedConnection < CHECK_CLOSED_CONNECTION_TIME) {
      return;
    }
    m_lastClearClosedConnection = time;

//begin check
    Iterator iterator = m_notUsedConnection.iterator();
    while (iterator.hasNext()) {
      ConnectionWrapper wrapper = (ConnectionWrapper) iterator.next();
      try {
        if (wrapper.connection.isClosed()) {
          iterator.remove();
        }
      }
      catch (Exception e) {
        iterator.remove();
        if (DEBUG) {
          System.out.println(
              "connection is closed, this connection initial StackTrace");
          wrapper.debugInfo.printStackTrace();
        }
      }
    }

//make connection pool size smaller if too big
    int decrease = getDecreasingConnectionCount();
    if (m_notUsedConnection.size() < decrease) {
      return;
    }

    while (decrease-- > 0) {
      ConnectionWrapper wrapper = (ConnectionWrapper) m_notUsedConnection.
          removeFirst();
      try {
        wrapper.connection.close();
      }
      catch (Exception e) {
      }
    }
  }

  /**
   * get increasing connection count, not just add 1 connection
   * @return count
   */
  public static int getIncreasingConnectionCount() {
    int count = 1;
    int current = getConnectionCount();
    count = current / 4;
    if (count < 1) {
      count = 1;
    }
    return count;
  }

  /**
   * get decreasing connection count, not just remove 1 connection
   * @return count
   */
  public static int getDecreasingConnectionCount() {
    int count = 0;
    int current = getConnectionCount();
    if (current < 10) {
      return 0;
    }
    return current / 3;
  }

  public synchronized static void printDebugMsg() {
    printDebugMsg(System.out);
  }

  public synchronized static void printDebugMsg(PrintStream out) {
    if (DEBUG == false) {
      return;
    }
    StringBuffer msg = new StringBuffer();
    msg.append("debug message in " + DBConnectionPool.class.getName());
    msg.append("\r\n");
    msg.append("total count is connection pool: " + getConnectionCount());
    msg.append("\r\n");
    msg.append("not used connection count: " + getNotUsedConnectionCount());
    msg.append("\r\n");
    msg.append("used connection, count: " + getUsedConnectionCount());
    out.println(msg);
    Iterator iterator = m_usedUsedConnection.iterator();
    while (iterator.hasNext()) {
      ConnectionWrapper wrapper = (ConnectionWrapper) iterator.next();
      wrapper.debugInfo.printStackTrace(out);
    }
    out.println();
  }

  public static synchronized int getNotUsedConnectionCount() {
    return m_notUsedConnection.size();
  }

  public static synchronized int getUsedConnectionCount() {
    return m_usedUsedConnection.size();
  }

  public static synchronized int getConnectionCount() {
    return m_notUsedConnection.size() + m_usedUsedConnection.size();
  }

  public static String getUrl() {
    return m_url;
  }

  public static void setUrl(String url) {
    if (url == null) {
      return;
    }
    m_url = url.trim();
  }

  public static String getUser() {
    return m_user;
  }

  public static void setUser(String user) {
    if (user == null) {
      return;
    }
    m_user = user.trim();
  }

  public static String getPassword() {
    return m_password;
  }

  public static void setPassword(String password) {
    if (password == null) {
      return;
    }
    m_password = password.trim();
  }

}

class ConnectionWrapper
    implements InvocationHandler {
  private final static String CLOSE_METHOD_NAME = "close";
  public Connection connection = null;
  private Connection m_originConnection = null;
  static final boolean DEBUG = true;
  public long lastAccessTime = System.currentTimeMillis();
  Throwable debugInfo = new Throwable("Connection initial statement");

  ConnectionWrapper(Connection con) {
    Class[] interfaces = {
        java.sql.Connection.class};
    this.connection = (Connection) Proxy.newProxyInstance(
        con.getClass().getClassLoader(),
        interfaces, this);
    m_originConnection = con;
  }
  void close() throws SQLException {
   if(DEBUG){
    System.out.println("it is close method");
   }
   
    m_originConnection.close();
  }

  public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
    Object obj = null;
    if (CLOSE_METHOD_NAME.equals(m.getName())) {
      DBConnectionPool.pushConnectionBackToPool(this);
    }
    else {
      obj = m.invoke(m_originConnection, args);
    }
    if (DEBUG) {
     System.out.println(m.getName()+"is invoke!");
    }
    lastAccessTime = System.currentTimeMillis();
    return obj;
  }

  public static void main(String[] args) {
    DBConnectionPool.setUrl(
        "jdbc:microsoft:sqlserver://192.168.0.76:1433;DatabaseName=sms_misc");
    DBConnectionPool.setUser("lhf");
    DBConnectionPool.setPassword("lhf");

    Connection con = DBConnectionPool.getConnection();
    Connection con1 = DBConnectionPool.getConnection();
    Connection con2 = DBConnectionPool.getConnection();

//do something with con ...
    try {
      Statement stmt1 = con.createStatement();
      Statement stmt2 = con1.createStatement();
      Statement stmt3 = con2.createStatement();

      for (int i = 0; i < 10; i++) {
       // stmt1.executeUpdate("exec testyh");
       // stmt2.executeUpdate("update yhgatemt_v3 set yh_status='wait'");
       // stmt3.executeUpdate("update yhgatemt_v3 set yh_status='past'");
      }
    }
    catch (Exception e) {
      System.out.println("error");
    }

    try {
     System.out.println("Closing con");
      con.close();
     
    }
    catch (Exception e) {}

    try {
     System.out.println("Closing con1");
      con1.close();
     
    }
    catch (Exception e) {}

    try {
      System.out.println("Closing con2");
      con2.close();
    
    }
    catch (Exception e) {}

    con = DBConnectionPool.getConnection();
    con1 = DBConnectionPool.getConnection();
    try {
      con1.close();
    }
    catch (Exception e) {}

    con2 = DBConnectionPool.getConnection();
    DBConnectionPool.printDebugMsg();

  }

}