关于InvocationHandler的学习心得

    技术2022-05-11  20

    InvocationHandler is the interface implemented by the invocation handler of a proxy instance.

     

     

    Each proxy instance has an associated invocation handler. When a method is invoked on a proxy instance, the method invocation is encoded and dispatched to the invoke method of its invocation handler.

     

     

     

    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 to

     

     

    Example

     

      ConnectionWrapper(Connection con) {

     

        Class[] interfaces = {

     

            java.sql.Connection.class};

     

        this.connection = (Connection) Proxy.newProxyInstance(

     

            con.getClass().getClassLoader(),

     

            interfaces, this);

     

        m_originConnection = con;

     

      }

     

    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InvocationHandlerinvoke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

     

      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;

     

      }

    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();

      }

    }

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     


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