I have followed this link What is the difference between closing Input/OutputStream and closing Socket directly? on how to close my java sockets. The problem after doing some jmap histo we find the number of sockets keep growing and but resultsets fluctuates. Snippet of my codes is as below.
BoneCP connectionPool = null;
class ConnectionHandler implements Runnable {
private Socket receivedSocketConn1;
ConnectionHandler(Socket receivedSocketConn1) {
this.receivedSocketConn1=receivedSocketConn1;
}
Connection dbconn = null;
public void run() { // etc
BufferedWriter writeBuffer = null;
BufferedReader readBuffer = null;
String capturedMessage="";
try{
dbconn = connectionPool.getConnection();
dbconn.setAutoCommit(false);
while ((nextChar=readBuffer.read()) != -1){
capturedMessage += (char) nextChar;
if (nextChar == '*')
{
try{
//all queries here.
//for insert query this how i do
Statement stmt1 = null;
stmt1 = dbconn.createStatement();
String insertQuery3 =........
count = stmt9.executeUpdate(insertQuery3);
try{
if ( stmt1!= null ){ stmt1.close();
}
else{
System.out.println("No stm1 exist");
}
}catch(SQLException ex){
System.out.println("SQLException has been caught for stmt1");
ex.printStackTrace(System.out);
}
///For select we do this
Statement stmt2 = null;
stmt2 = dbconn.createStatement();
String selectQuery2= .........
ResultSet rs2 = stmt2.executeQuery(selectQuery2);
if(rs2.next())
{
}
try{
if ( rs2!= null ){
rs2.close();
} else{
System.out.println("No rs2 exist");
}
if ( stmt2!= null ){
stmt2.close();
} else{
System.out.println("No stm2 exist");
}
}catch(SQLException ex)
{
System.out.println("SQLException has been caught for stmt2");
ex.printStackTrace(System.out);
}
dbconn.commit
}
catch (SQLException ex){
ex.printStackTrace(System.out);
try{
dbconn.rollback();
}
catch (Exception rollback){
rollback.printStackTrace(System.out);
}
}
catch (Exception e){
e.printStackTrace(System.out);
try{
dbconn.rollback();
}
catch (Exception rollback){
rollback.printStackTrace(System.out);
}
}
finally
{
}
}
catch (SocketTimeoutException ex){
ex.printStackTrace();
}
catch (IOException ex){
ex.printStackTrace();
}
catch (Exception ex){
ex.printStackTrace(System.out);
}
finally{
try{
if ( dbconn != null ){
dbconn.close();
}
else{
System.out.println("dbConn is null in finally close");
}
}
catch(SQLException ex){
ex.printStackTrace();
}
try{
if ( writeBuffer != null ){
writeBuffer.close();
//new changes added but no effect.
readBuffer = null;
writeBuffer =null;
receivedSocketConn1=null;
}
else{
System.out.println("writeBuffer is null in finally close");
}
}
catch(IOException ex){
ex.printStackTrace(System.out);
}
}
}
}
Just to verify further I stripped down my codes to just have the socket application part and remove all other codes. Below is the jmap histo before any socket connection.
num #instances #bytes class name
----------------------------------------------
1: 6023 824664 <methodKlass>
2: 6023 726808 <constMethodKlass>
3: 401 458376 <constantPoolKlass>
4: 369 296320 <constantPoolCacheKlass>
5: 401 293848 <instanceKlassKlass>
6: 439 225264 [I
7: 1512 165736 [C
8: 772 144224 [B
9: 461 56120 java.lang.Class
10: 674 42880 [[I
11: 602 39424 [S
12: 1189 38048 java.lang.String
13: 43 25112 <objArrayKlassKlass>
14: 339 14896 [Ljava.lang.Object;
15: 8 4672 <typeArrayKlassKlass>
16: 112 3584 java.util.Hashtable$Entry
17: 47 3384 java.lang.reflect.Field
18: 132 3168 java.lang.StringBuilder
19: 66 2352 [Ljava.lang.String;
20: 25 2128 [Ljava.util.HashMap$Entry;
21: 11 2112 <klassKlass>
22: 38 1824 sun.util.locale.LocaleObjectCache$CacheEntry
23: 28 1792 java.net.URL
24: 74 1776 java.io.File
25: 12 1760 [Ljava.util.Hashtable$Entry;
26: 54 1728 java.util.concurrent.ConcurrentHashMap$HashEntry
27: 48 1536 java.util.HashMap$Entry
28: 36 1440 java.util.concurrent.ConcurrentHashMap$Segment
29: 52 1408 [Ljava.util.concurrent.ConcurrentHashMap$HashEntry;
30: 3 1400 <methodDataKlass>
31: 33 1320 java.lang.ref.Finalizer
32: 16 1152 java.lang.reflect.Constructor
33: 36 1152 java.util.concurrent.locks.ReentrantLock$NonfairSync
34: 40 960 java.util.LinkedList$Node
35: 24 960 java.util.LinkedHashMap$Entry
36: 19 912 java.util.HashMap
37: 20 800 sun.util.locale.BaseLocale$Key
38: 9 720 [Ljava.util.WeakHashMap$Entry;
39: 21 672 java.util.LinkedList
40: 42 672 java.lang.Object
41: 16 640 java.io.ObjectStreamField
42: 16 640 java.lang.ref.SoftReference
43: 32 632 [Ljava.lang.Class;
44: 6 624 java.lang.Thread
45: 19 608 sun.util.locale.BaseLocale
46: 25 600 java.net.Parts
47: 12 576 sun.misc.URLClassPath$JarLoader
48: 22 528 sun.security.action.GetPropertyAction
49: 6 480 java.util.jar.JarFile$JarFileEntry
50: 20 480 java.io.ExpiringCache$Entry
51: 20 480 java.util.Locale$LocaleKey
52: 6 480 [Ljava.util.concurrent.ConcurrentHashMap$Segment;
53: 19 456 java.util.Locale
54: 11 440 java.util.WeakHashMap$Entry
55: 9 432 sun.nio.cs.UTF_8$Encoder
56: 9 432 java.util.WeakHashMap
57: 6 384 java.util.jar.JarFile
58: 6 384 java.util.zip.ZipEntry
59: 6 384 java.nio.DirectByteBuffer
60: 12 384 java.lang.ref.ReferenceQueue
61: 16 384 java.lang.StringBuffer
62: 6 336 java.util.zip.ZipFile$ZipFileInputStream
63: 6 336 java.nio.DirectLongBufferU
64: 6 336 java.util.zip.ZipFile$ZipFileInflaterInputStream
65: 10 320 java.security.AccessControlContext
66: 13 312 sun.misc.URLClassPath$3
67: 6 288 java.util.concurrent.ConcurrentHashMap
68: 8 256 java.util.Vector
69: 8 256 java.lang.OutOfMemoryError
70: 5 248 [Ljava.lang.reflect.Field;
71: 2 224 java.net.SocksSocketImpl
72: 14 224 java.lang.ref.ReferenceQueue$Lock
73: 8 208 [Ljava.io.ObjectStreamField;
74: 8 192 [Ljava.lang.reflect.Constructor;
75: 8 192 java.lang.Class$1
76: 8 192 sun.reflect.NativeConstructorAccessorImpl
77: 8 192 java.util.ArrayList
78: 4 192 java.util.Hashtable
79: 6 192 java.util.zip.Inflater
80: 4 192 java.nio.HeapByteBuffer
81: 6 192 java.util.zip.ZipCoder
82: 4 192 java.nio.HeapCharBuffer
83: 7 168 java.io.FileDescriptor
84: 5 160 java.io.DataInputStream
85: 2 160 java.lang.reflect.Method
86: 6 144 sun.misc.MetaIndex
87: 6 144 sun.misc.FileURLMapper
88: 6 144 java.util.zip.ZStreamRef
89: 6 144 java.util.ArrayDeque
90: 6 144 sun.misc.PerfCounter
91: 8 128 sun.reflect.DelegatingConstructorAccessorImpl
92: 8 128 java.util.concurrent.atomic.AtomicInteger
93: 3 120 java.security.ProtectionDomain
94: 3 120 sun.nio.cs.UTF_8$Decoder
95: 2 112 java.util.LinkedHashMap
96: 2 112 java.io.ExpiringCache$1
97: 2 112 sun.nio.cs.StreamEncoder
98: 1 104 java.lang.ref.Reference$ReferenceHandler
99: 1 104 java.lang.ref.Finalizer$FinalizerThread
100: 1 104 sun.net.www.protocol.file.FileURLConnection
101: 2 96 java.lang.ThreadGroup
102: 3 96 java.util.Stack
103: 2 96 java.io.BufferedReader
104: 3 96 java.security.CodeSource
105: 2 96 java.io.BufferedWriter
106: 2 96 sun.nio.cs.StreamDecoder
107: 2 96 java.util.Properties
108: 6 96 sun.misc.URLClassPath$JarLoader$1
109: 3 96 java.io.FileInputStream
110: 2 96 java.util.StringTokenizer
111: 2 88 [Ljava.net.URL;
112: 2 80 java.io.ExpiringCache
113: 1 80 sun.misc.Launcher$ExtClassLoader
114: 1 80 [Ljava.lang.ThreadLocal$ThreadLocalMap$Entry;
115: 2 80 sun.misc.URLClassPath
116: 5 80 java.lang.ThreadLocal
117: 1 80 sun.misc.Launcher$AppClassLoader
118: 3 72 java.util.Collections$SynchronizedSet
119: 3 72 java.lang.RuntimePermission
120: 3 72 sun.misc.Signal
121: 2 64 java.io.FileOutputStream
122: 4 64 java.lang.Class$3
123: 2 64 java.io.FilePermission
124: 2 64 java.lang.VirtualMachineError
125: 2 64 java.lang.ClassLoader$NativeLibrary
126: 2 64 [Ljava.lang.Thread;
127: 2 64 java.lang.ref.ReferenceQueue$Null
128: 2 64 java.lang.ThreadLocal$ThreadLocalMap$Entry
129: 2 64 java.io.PrintStream
130: 2 64 java.io.OutputStreamWriter
131: 1 48 [J
132: 2 48 java.net.InetAddress$Cache
133: 2 48 java.net.InetAddress$Cache$Type
134: 2 48 java.net.URLClassLoader$1
135: 1 48 java.util.Hashtable$Enumerator
136: 3 48 java.lang.ClassLoader$3
137: 3 48 java.security.ProtectionDomain$Key
138: 3 48 [Ljava.security.Principal;
139: 3 48 java.lang.Integer
140: 3 48 java.util.HashSet
141: 3 48 sun.reflect.ReflectionFactory$GetReflectionFactoryAction
142: 2 48 sun.misc.NativeSignalHandler
143: 2 48 java.io.BufferedOutputStream
144: 2 48 java.nio.charset.CoderResult
145: 3 48 java.nio.charset.CodingErrorAction
146: 2 48 [Ljava.io.File;
147: 1 40 java.util.HashMap$EntryIterator
148: 1 40 java.security.PrivilegedActionException
149: 1 40 java.io.BufferedInputStream
154: 1 32 java.net.InetAddress
160: 1 32 java.lang.NoSuchMethodError
176: 1 32 java.net.Socket
193: 1 24 java.io.FileReader
194: 1 24 java.net.Inet4AddressImpl
195: 1 24 java.io.FilePermissionCollection
196: 1 24 sun.util.locale.BaseLocale$Cache
197: 1 24 java.lang.reflect.ReflectPermission
198: 1 24 java.lang.ThreadLocal$ThreadLocalMap
199: 1 24 java.util.BitSet
200: 1 24 sun.net.sdp.SdpProvider
201: 1 24 [Ljava.lang.reflect.Method;
202: 1 24 java.net.InetSocketAddress
Jmap after closing 50 socket connections. Just compare this java.net.Socket can see a hike to 51.
num #instances #bytes class name
----------------------------------------------
1: 7823 1070328 <methodKlass>
2: 7823 983752 <constMethodKlass>
3: 5717 971936 [C
4: 536 635152 <constantPoolKlass>
5: 495 413664 <constantPoolCacheKlass>
6: 744 410336 [I
7: 536 390976 <instanceKlassKlass>
8: 711 255152 [B
9: 2612 83584 java.lang.String
10: 611 75240 java.lang.Class
11: 832 58080 [S
12: 876 54520 [[I
13: 58 33872 <objArrayKlassKlass>
14: 1218 29232 java.lang.StringBuilder
15: 41 22576 <methodDataKlass>
16: 350 17688 [Ljava.lang.Object;
17: 269 12912 java.nio.HeapCharBuffer
18: 41 5904 java.text.DecimalFormat
19: 52 5824 java.net.SocksSocketImpl
20: 310 4960 java.lang.Object
21: 8 4672 <typeArrayKlassKlass>
22: 40 4480 java.util.GregorianCalendar
23: 40 3840 sun.util.calendar.Gregorian$Date
24: 89 3832 [Ljava.lang.String;
25: 117 3744 java.util.concurrent.ConcurrentHashMap$HashEntry
26: 111 3552 java.util.HashMap$Entry
27: 88 3520 java.lang.ref.Finalizer
28: 109 3488 java.util.Hashtable$Entry
29: 8 3200 commServer8000$ConnectionHandler
30: 80 3200 java.util.concurrent.ConcurrentHashMap$Segment
31: 39 3144 [Ljava.util.HashMap$Entry;
32: 88 2816 java.lang.StackTraceElement
33: 39 2808 java.lang.reflect.Field
34: 41 2624 java.text.DecimalFormatSymbols
35: 80 2560 java.util.concurrent.locks.ReentrantLock$NonfairSync
36: 40 2560 java.text.SimpleDateFormat
37: 50 2400 java.net.SocketInputStream
38: 37 2368 java.net.URL
39: 42 2352 sun.util.calendar.ZoneInfo
40: 32 2304 java.lang.reflect.Constructor
41: 80 2304 [Ljava.util.concurrent.ConcurrentHashMap$HashEntry;
42: 3 2120 [J
43: 11 2112 <klassKlass>
44: 128 2048 java.lang.Character
45: 41 1968 sun.util.locale.LocaleObjectCache$CacheEntry
46: 41 1640 java.text.DigitList
47: 51 1632 java.net.Inet4Address
48: 51 1632 java.net.Socket
49: 40 1600 [Z
50: 40 1600 java.util.LinkedHashMap$Entry
51: 19 1520 [Ljava.util.concurrent.ConcurrentHashMap$Segment;
52: 31 1488 java.util.HashMap
53: 61 1464 java.io.FileDescriptor
54: 14 1456 java.lang.Thread
55: 8 1088 [Ljava.util.Hashtable$Entry;
56: 43 1032 java.util.LinkedList$Node
57: 63 1008 java.util.concurrent.atomic.AtomicInteger
58: 25 1000 java.lang.ref.SoftReference
59: 40 960 java.util.Date
60: 19 912 java.util.concurrent.ConcurrentHashMap
61: 18 864 java.nio.HeapByteBuffer
62: 21 840 sun.util.locale.BaseLocale$Key
63: 17 816 sun.nio.cs.UTF_8$Encoder
64: 17 816 sun.misc.URLClassPath$JarLoader
65: 32 768 java.io.ExpiringCache$Entry
66: 9 720 [Ljava.util.WeakHashMap$Entry;
67: 22 704 java.util.LinkedList
68: 21 672 sun.util.locale.BaseLocale
69: 16 640 java.io.ObjectStreamField
70: 18 576 java.security.AccessControlContext
71: 10 560 sun.nio.cs.StreamEncoder
72: 10 544 [Ljava.lang.StackTraceElement;
73: 1 528 [Ljava.lang.Character;
85: 8 384 java.io.BufferedReader
86: 6 384 java.nio.DirectByteBuffer
87: 8 384 sun.nio.cs.StreamDecoder
88: 8 384 java.net.SocketOutputStream
89: 9 360 sun.nio.cs.UTF_8$Decoder
90: 6 336 java.util.LinkedHashMap
94: 6 336 java.util.zip.ZipFile$ZipFileInflaterInputStream
95: 8 320 java.net.SocketTimeoutException
96: 10 320 java.io.OutputStreamWriter
97: 8 320 java.util.IdentityHashMap
98: 13 312 java.io.File
99: 18 296 [Ljava.lang.Class;
100: 12 288 sun.misc.MetaIndex
101: 6 288 java.util.Hashtable
102: 17 272 java.lang.ref.ReferenceQueue$Lock
103: 8 256 java.net.InetAddress
104: 8 256 java.util.Vector
105: 16 256 sun.reflect.DelegatingConstructorAccessorImpl
106: 8 256 java.lang.OutOfMemoryError
107: 5 248 [Ljava.lang.reflect.Field;
108: 6 240 java.util.WeakHashMap$Entry
109: 7 224 java.util.ResourceBundle$LoaderReference
110: 7 224 java.io.FileInputStream
111: 9 216 java.util.ArrayList
112: 9 216 java.util.Collections$SetFromMap
113: 8 208 [Ljava.io.ObjectStreamField;
114: 2 192 [Ljava.text.DateFormat$Field;
115: 8 192 java.math.RoundingMode
116: 8 192 java.io.InputStreamReader
117: 6 192 java.util.zip.Inflater
118: 6 192 java.util.zip.ZipCoder
119: 8 192 [Ljava.security.ProtectionDomain;
120: 7 168 sun.security.action.GetPropertyAction
121: 4 160 java.security.ProtectionDomain
122: 10 160 java.lang.Integer
123: 2 160 [Ljava.lang.ThreadLocal$ThreadLocalMap$Entry;
124: 4 160 java.util.Collections$SingletonMap
125: 6 144 java.util.zip.ZStreamRef
126: 6 144 java.util.ArrayDeque
127: 6 144 sun.misc.PerfCounter
128: 4 128 java.util.Stack
129: 4 128 java.security.CodeSource
130: 4 128 sun.util.LocaleServiceProviderPool
131: 8 128 java.lang.Throwable$WrappedPrintStream
132: 8 128 java.util.IdentityHashMap$KeySet
133: 3 120 sun.misc.URLClassPath
134: 2 112 java.io.ExpiringCache$1
135: 7 112 java.net.Socket$3
136: 7 112 java.net.Socket$2
137: 7 112 java.lang.ThreadLocal
138: 1 104 java.lang.ref.Reference$ReferenceHandler
139: 1 104 java.lang.ref.Finalizer$FinalizerThread
140: 2 96 java.lang.ThreadGroup
141: 4 96 java.util.Collections$UnmodifiableRandomAccessList
142: 3 96 java.lang.ClassLoader$NativeLibrary
143: 2 96 java.util.Properties
144: 3 96 java.lang.ThreadLocal$ThreadLocalMap$Entry
145: 2 80 java.io.ExpiringCache
146: 2 80 java.util.Locale$Category
147: 1 80 sun.misc.Launcher$ExtClassLoader
148: 1 80 sun.misc.Launcher$AppClassLoader
149: 1 80 java.lang.reflect.Method
150: 3 72 java.util.Collections$SynchronizedSet
151: 3 72 java.lang.RuntimePermission
152: 3 72 sun.misc.Signal
153: 3 72 java.util.Arrays$ArrayList
154: 2 64 java.io.FileOutputStream
155: 1 64 java.util.ResourceBundle$RBClassLoader
156: 2 64 java.lang.VirtualMachineError
157: 4 64 java.security.ProtectionDomain$Key
158: 4 64 [Ljava.security.Principal;
159: 2 64 [Ljava.lang.Thread;
160: 4 64 java.util.LinkedHashSet
161: 2 64 java.lang.ref.ReferenceQueue$Null
162: 2 64 sun.nio.fs.UnixPath
163: 2 64 java.io.PrintStream
164: 2 64 sun.util.locale.UnicodeLocaleExtension
165: 1 56 java.text.DateFormatSymbols
166: 3 48 java.text.AttributedCharacterIterator$Attribute
167: 2 48 java.net.InetAddress$Cache
168: 2 48 java.net.InetAddress$Cache$Type
169: 1 48 [Ljava.math.RoundingMode;
170: 2 48 sun.util.locale.LocaleExtensions
171: 3 48 java.util.HashSet
172: 2 48 java.lang.ThreadLocal$ThreadLocalMap
173: 2 48 sun.misc.NativeSignalHandler
174: 3 48 sun.net.www.protocol.jar.Handler
175: 2 48 java.io.BufferedOutputStream
176: 2 48 java.nio.charset.CoderResult
177: 3 48 java.nio.charset.CodingErrorAction
178: 1 40 java.util.ResourceBundle$1
179: 1 40 java.io.BufferedInputStream
180: 1 40 sun.text.resources.FormatData
181: 1 40 sun.text.resources.FormatData_en
182: 1 40 sun.text.resources.FormatData_en_US
183: 1 40 sun.util.resources.CurrencyNames
184: 1 40 sun.misc.Cleaner
185: 1 40 sun.util.resources.CurrencyNames_en_US
186: 1 40 sun.nio.cs.StandardCharsets$Aliases
187: 1 40 sun.util.resources.CalendarData
188: 1 40 sun.util.resources.CalendarData_en
189: 1 40 sun.nio.cs.StandardCharsets$Classes
190: 1 40 sun.nio.cs.StandardCharsets$Cache
214: 1 24 sun.nio.cs.US_ASCII
215: 1 24 sun.nio.cs.ISO_8859_1
216: 1 24 java.net.Inet6AddressImpl
217: 1 24 sun.nio.fs.NativeBuffer$Deallocator
218: 1 24 sun.nio.cs.UTF_16BE
219: 1 24 sun.nio.cs.UTF_16LE
220: 1 24 java.util.Locale$Cache
221: 1 24 sun.nio.cs.UTF_16
222: 1 24 java.io.FilePermissionCollection
223: 1 24 sun.util.locale.BaseLocale$Cache
224: 1 24 java.lang.reflect.ReflectPermission
225: 1 24 java.util.BitSet
226: 1 24 sun.net.sdp.SdpProvider
227: 1 24 [Ljava.lang.reflect.Method;
228: 1 24 sun.misc.JarIndex
229: 1 24 java.net.ServerSocket
