decrease JdbcParameter memory used

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterDate.java

@@ -5,7 +5,6 @@ import java.util.Calendar;
 import java.util.Date;
 
 public final class JdbcParameterDate implements JdbcParameter {
-
     private final Date value;
 
     public JdbcParameterDate(Date value){

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterDecimal.java

@@ -6,12 +6,32 @@ import java.util.Calendar;
 
 public final class JdbcParameterDecimal implements JdbcParameter {
 
-    private final BigDecimal value;
+    private final BigDecimal           value;
 
-    public JdbcParameterDecimal(BigDecimal value){
+    public static JdbcParameterDecimal NULL = new JdbcParameterDecimal(null);
+    public static JdbcParameterDecimal ZERO = new JdbcParameterDecimal(BigDecimal.ZERO);
+    public static JdbcParameterDecimal TEN = new JdbcParameterDecimal(BigDecimal.TEN);
+    
+    private JdbcParameterDecimal(BigDecimal value){
         this.value = value;
     }
 
+    public static JdbcParameterDecimal valueOf(BigDecimal x) {
+        if (x == null) {
+            return NULL;
+        }
+        
+        if (x == BigDecimal.ZERO) {
+            return ZERO;
+        }
+        
+        if (x == BigDecimal.TEN) {
+            return TEN;
+        }
+        
+        return new JdbcParameterDecimal(x);
+    }
+
     @Override
     public Object getValue() {
         return value;

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterInt.java

@@ -4,12 +4,30 @@ import java.sql.Types;
 import java.util.Calendar;
 
 public final class JdbcParameterInt implements JdbcParameter {
+    
+    private static JdbcParameterInt[] cache;
+    
+    static {
+        int cacheSize = 127;
+        cache = new JdbcParameterInt[cacheSize];
+        for (int i = 0; i < cache.length; ++i) {
+            cache[i] = new JdbcParameterInt(i);
+        }
+    }
 
     private final int value;
 
-    public JdbcParameterInt(int value){
+    private JdbcParameterInt(int value){
         this.value = value;
     }
+    
+    public static JdbcParameterInt valueOf(int value) {
+        if (value >= 0 && value < cache.length) {
+            return cache[value];
+        }
+        
+        return new JdbcParameterInt(value);
+    }
 
     @Override
     public Object getValue() {

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterLong.java

@@ -4,12 +4,29 @@ import java.sql.Types;
 import java.util.Calendar;
 
 public final class JdbcParameterLong implements JdbcParameter {
-
+    private static JdbcParameterLong[] cache;
+    
+    static {
+        int cacheSize = 127;
+        cache = new JdbcParameterLong[cacheSize];
+        for (int i = 0; i < cache.length; ++i) {
+            cache[i] = new JdbcParameterLong(i);
+        }
+    }
+    
     private final long value;
 
-    public JdbcParameterLong(long value){
+    private JdbcParameterLong(long value){
         this.value = value;
     }
+    
+    public static JdbcParameterLong valueOf(long value) {
+        if (value >= 0 && value < cache.length) {
+            return cache[(int) value];
+        }
+        
+        return new JdbcParameterLong(value);
+    }
 
     @Override
     public Object getValue() {

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterNull.java

@@ -1,12 +1,36 @@
 package com.alibaba.druid.proxy.jdbc;
 
+import java.sql.Types;
 import java.util.Calendar;
 
 public final class JdbcParameterNull implements JdbcParameter {
 
-    private final int sqlType;
+    private final int                     sqlType;
 
-    public JdbcParameterNull(int sqlType){
+    public final static JdbcParameterNull CHAR      = new JdbcParameterNull(Types.CHAR);
+    public final static JdbcParameterNull VARCHAR   = new JdbcParameterNull(Types.VARCHAR);
+    public final static JdbcParameterNull NVARCHAR  = new JdbcParameterNull(Types.NVARCHAR);
+
+    public final static JdbcParameterNull BINARY    = new JdbcParameterNull(Types.BINARY);
+    public final static JdbcParameterNull VARBINARY = new JdbcParameterNull(Types.VARBINARY);
+
+    public final static JdbcParameterNull TINYINT   = new JdbcParameterNull(Types.TINYINT);
+    public final static JdbcParameterNull SMALLINT  = new JdbcParameterNull(Types.SMALLINT);
+    public final static JdbcParameterNull INTEGER   = new JdbcParameterNull(Types.INTEGER);
+    public final static JdbcParameterNull BIGINT    = new JdbcParameterNull(Types.BIGINT);
+
+    public final static JdbcParameterNull DECIMAL   = new JdbcParameterNull(Types.DECIMAL);
+    public final static JdbcParameterNull NUMERIC   = new JdbcParameterNull(Types.NUMERIC);
+    public final static JdbcParameterNull FLOAT     = new JdbcParameterNull(Types.FLOAT);
+    public final static JdbcParameterNull DOUBLE    = new JdbcParameterNull(Types.DOUBLE);
+
+    public final static JdbcParameterNull NULL      = new JdbcParameterNull(Types.NULL);
+
+    public final static JdbcParameterNull DATE      = new JdbcParameterNull(Types.DATE);
+    public final static JdbcParameterNull TIME      = new JdbcParameterNull(Types.TIME);
+    public final static JdbcParameterNull TIMESTAMP = new JdbcParameterNull(Types.TIMESTAMP);
+
+    private JdbcParameterNull(int sqlType){
         this.sqlType = sqlType;
     }
 
@@ -30,4 +54,50 @@ public final class JdbcParameterNull implements JdbcParameter {
         return sqlType;
     }
 
+    public static JdbcParameterNull valueOf(int sqlType) {
+        switch (sqlType) {
+            case Types.TINYINT:
+                return INTEGER;
+            case Types.SMALLINT:
+                return SMALLINT;
+            case Types.INTEGER:
+                return INTEGER;
+            case Types.BIGINT:
+                return BIGINT;
+
+            case Types.DECIMAL:
+                return DECIMAL;
+            case Types.NUMERIC:
+                return NUMERIC;
+            case Types.FLOAT:
+                return FLOAT;
+            case Types.DOUBLE:
+                return DOUBLE;
+
+            case Types.CHAR:
+                return CHAR;
+            case Types.VARCHAR:
+                return VARCHAR;
+            case Types.NVARCHAR:
+                return NVARCHAR;
+
+            case Types.BINARY:
+                return BINARY;
+            case Types.VARBINARY:
+                return VARBINARY;
+
+            case Types.TIME:
+                return TIME;
+            case Types.DATE:
+                return DATE;
+            case Types.TIMESTAMP:
+                return TIMESTAMP;
+
+            case Types.NULL:
+                return NULL;
+
+            default:
+                return new JdbcParameterNull(sqlType);
+        }
+    }
 }

src/main/java/com/alibaba/druid/proxy/jdbc/PreparedStatementProxyImpl.java

@@ -612,30 +612,47 @@ public class PreparedStatementProxyImpl extends StatementProxyImpl implements Pr
     }
 
     private JdbcParameter createParemeter(int x) {
-        return new JdbcParameterInt(x);
+        return JdbcParameterInt.valueOf(x);
     }
 
     private JdbcParameter createParameter(long x) {
-        return new JdbcParameterLong(x);
+        return JdbcParameterLong.valueOf(x);
     }
 
     private JdbcParameter createParameterNull(int sqlType) {
-        return new JdbcParameterNull(sqlType);
+        return JdbcParameterNull.valueOf(sqlType);
+
     }
 
     private JdbcParameter createParameter(java.util.Date x) {
+        if (x == null) {
+            return JdbcParameterNull.DATE;
+        }
+        
         return new JdbcParameterDate(x);
     }
 
     private JdbcParameter createParameter(BigDecimal x) {
-        return new JdbcParameterDecimal(x);
+        if (x == null) {
+            return JdbcParameterNull.DECIMAL;
+        }
+        
+        return JdbcParameterDecimal.valueOf(x);
     }
 
     private JdbcParameter createParameter(String x) {
+        if (x == null) {
+            return JdbcParameterNull.VARCHAR;
+        }
+        
         return new JdbcParameterString(x);
     }
 
     private JdbcParameter createParameter(Timestamp x) {
+        if (x == null) {
+            return JdbcParameterNull.TIMESTAMP;
+        }
+        
         return new JdbcParameterTimestamp(x);
     }