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）
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;
}
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();
}
}
