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From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
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Subject: Re: Is this the way to work with try with resources
Date: Wed, 9 Aug 2017 23:03:46 -0400
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On 8/9/2017 8:53 PM, Arne Vajhøj wrote:
> The "magic" sauce:

> public class Reveal {

Well magic or not - it did have some bad concurrency
problem as I did not get all the synchronized in.

New version below.

Arne

import java.io.PrintStream;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.HashSet;
import java.util.Set;

public class Reveal {
     public static interface TrackableResource {
         public String getId() throws SQLException;
     }
     private static Set<TrackableResource> reslst = new 
HashSet<TrackableResource>();
     public static class ResultSetWrapper implements InvocationHandler, 
TrackableResource {
         private static int count = 0;
         private int num;
         private ResultSet rs;
         private String parent;
         private String sql;
         public ResultSetWrapper(ResultSet rs, String parent) {
             this.rs = rs;
             this.parent = parent;
             this.sql = null;
             synchronized(reslst) {
                 count++;
                 num = count;
                 reslst.add(this);
             }
         }
         public ResultSetWrapper(ResultSet rs, String parent, String sql) {
             this.rs = rs;
             this.parent = parent;
             this.sql = sql;
             synchronized(reslst) {
                 count++;
                 num = count;
                 reslst.add(this);
             }
         }
         public Object invoke(Object proxy, Method method, Object[] 
args) throws Throwable {
             if(method.getName().equals("close")) {
                 synchronized(reslst) {
                     reslst.remove(this);
                 }
                 return method.invoke(rs, args);
             } else {
                 return method.invoke(rs, args);
             }
         }
         public String getId() throws SQLException {
             if(sql == null) {
                 return "ResultSet#" + num + " from " + parent;
             } else {
                 return "ResultSet#" + num + " (" + sql + ") from " + 
parent;
             }
         }
     }
     public static class PreparedStatementWrapper implements 
InvocationHandler, TrackableResource {
         private static int count = 0;
         private int num;
         private Statement stmt;
         private String parent;
         private String sql;
         public PreparedStatementWrapper(Statement stmt, String parent, 
String sql) {
             this.stmt = stmt;
             this.parent = parent;
             this.sql = sql;
             synchronized(reslst) {
                 count++;
                 num = count;
                 reslst.add(this);
             }
         }
         public Object invoke(Object proxy, Method method, Object[] 
args) throws Throwable {
             if(method.getName().equals("close")) {
                 synchronized(reslst) {
                     reslst.remove(this);
                 }
                 return method.invoke(stmt, args);
             } else if(method.getName().equals("executeQuery")) {
                 return 
(ResultSet)Proxy.newProxyInstance(getClass().getClassLoader(), new 
Class<?>[] { ResultSet.class },
                                                          new 
ResultSetWrapper((ResultSet)method.invoke(stmt, args), getId()));
             } else {
                 return method.invoke(stmt, args);
             }
         }
         public String getId() throws SQLException {
             return "PreparedStatement#" + num + " (" + sql + ") from " 
+ parent;
         }
     }
     public static class StatementWrapper implements InvocationHandler, 
TrackableResource {
         private static int count = 0;
         private int num;
         private Statement stmt;
         private String parent;
         public StatementWrapper(Statement stmt, String parent) {
             this.stmt = stmt;
             this.parent = parent;
             synchronized(reslst) {
                 count++;
                 num = count;
                 reslst.add(this);
             }
         }
         public Object invoke(Object proxy, Method method, Object[] 
args) throws Throwable {
             if(method.getName().equals("close")) {
                 synchronized(reslst) {
                     reslst.remove(this);
                 }
                 return method.invoke(stmt, args);
             } else if(method.getName().equals("executeQuery")) {
                 return 
(ResultSet)Proxy.newProxyInstance(getClass().getClassLoader(), new 
Class<?>[] { ResultSet.class },
                                                          new 
ResultSetWrapper((ResultSet)method.invoke(stmt, args), getId(), 
(String)args[0]));
             } else {
                 return method.invoke(stmt, args);
             }
         }
         public String getId() throws SQLException {
             return "Statement#" + num + " from " + parent;
         }
     }
     public static class ConnectionWrapper implements InvocationHandler, 
TrackableResource {
         private static int count = 0;
         private int num;
         private Connection con;
         public ConnectionWrapper(Connection con) {
             this.con = con;
             synchronized(reslst) {
                 count++;
                 num = count;
                 reslst.add(this);
             }
         }
         public Object invoke(Object proxy, Method method, Object[] 
args) throws Throwable {
             if(method.getName().equals("close")) {
                 synchronized(reslst) {
                     reslst.remove(this);
                 }
                 return method.invoke(con, args);
             } else if(method.getName().equals("createStatement")) {
                 return 
(Statement)Proxy.newProxyInstance(con.getClass().getClassLoader(), new 
Class<?>[] { Statement.class },
                                                          new 
StatementWrapper((Statement)method.invoke(con, args), getId()));
             } else if(method.getName().equals("prepareStatement")) {
                 return 
(PreparedStatement)Proxy.newProxyInstance(con.getClass().getClassLoader(), 
new Class<?>[] { PreparedStatement.class },
                                                                  new 
PreparedStatementWrapper((PreparedStatement)method.invoke(con, args), 
getId(), (String)args[0]));
             } else {
                 return method.invoke(con, args);
             }
         }
         public String getId() throws SQLException {
             return "Connection#" + num;
         }
     }
     public static Connection wrap(Connection con) {
         return 
(Connection)Proxy.newProxyInstance(con.getClass().getClassLoader(), new 
Class<?>[] { Connection.class },
                                                   new 
ConnectionWrapper(con));
     }
     public static void dumpOpen(PrintStream ps) throws SQLException {
         synchronized(reslst) {
             for(TrackableResource obj : reslst.toArray(new 
TrackableResource[0])) {
                 System.out.println("Unclosed: " + obj.getId());
             }
         }
     }
}