diff --git a/pom.xml b/pom.xml
index 964a408..693116f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -42,6 +42,7 @@
         <groovy.version>3.0.9</groovy.version>
         <groovy-sandbox.version>1.27</groovy-sandbox.version>
         <commons-lang3.version>3.11</commons-lang3.version>
+        <guava.version>30.1.1-jre</guava.version>
         <maven-assembly-plugin.version>2.5.5</maven-assembly-plugin.version>
     </properties>
 
@@ -123,6 +124,13 @@
             <scope>provided</scope>
         </dependency>
 
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+            <scope>provided</scope>
+        </dependency>
+
         <!-- Test scope -->
         <dependency>
             <groupId>junit</groupId>
diff --git a/src/main/java/io/gravitee/policy/groovy/GroovyInitializer.java b/src/main/java/io/gravitee/policy/groovy/GroovyInitializer.java
index 275556c..a948079 100644
--- a/src/main/java/io/gravitee/policy/groovy/GroovyInitializer.java
+++ b/src/main/java/io/gravitee/policy/groovy/GroovyInitializer.java
@@ -28,19 +28,25 @@
 public class GroovyInitializer implements PolicyContext, PolicyContextProviderAware {
 
     private Environment environment;
+    private boolean classLoaderLegacyMode = true;
 
     @Override
     public void onActivation() throws Exception {
-        SecuredResolver.initialize(this.environment);
+        if (classLoaderLegacyMode || !SecuredResolver.isInitialized()) {
+            SecuredResolver.initialize(this.environment);
+        }
     }
 
     @Override
     public void onDeactivation() throws Exception {
-        SecuredResolver.destroy();
+        if (classLoaderLegacyMode) {
+            SecuredResolver.destroy();
+        }
     }
 
     @Override
     public void setPolicyContextProvider(PolicyContextProvider policyContextProvider) {
         this.environment = policyContextProvider.getComponent(Environment.class);
+        this.classLoaderLegacyMode = environment.getProperty("classloader.legacy.enabled", Boolean.class, true);
     }
 }
diff --git a/src/main/java/io/gravitee/policy/groovy/sandbox/SecuredGroovyShell.java b/src/main/java/io/gravitee/policy/groovy/sandbox/SecuredGroovyShell.java
index 19ff1d0..022eb6c 100644
--- a/src/main/java/io/gravitee/policy/groovy/sandbox/SecuredGroovyShell.java
+++ b/src/main/java/io/gravitee/policy/groovy/sandbox/SecuredGroovyShell.java
@@ -15,25 +15,18 @@
  */
 package io.gravitee.policy.groovy.sandbox;
 
-import static org.codehaus.groovy.ast.tools.GeneralUtils.classX;
-import static org.codehaus.groovy.ast.tools.GeneralUtils.propX;
-
+import com.google.common.cache.Cache;
+import com.google.common.cache.CacheBuilder;
 import groovy.lang.Binding;
 import groovy.lang.GroovyCodeSource;
 import groovy.lang.GroovyShell;
 import groovy.lang.Script;
-import groovy.transform.ThreadInterrupt;
-import groovy.transform.TimedInterrupt;
 import io.gravitee.policy.groovy.GroovyPolicy;
 import io.gravitee.policy.groovy.utils.Sha1;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
-import java.util.concurrent.TimeUnit;
+import java.time.Duration;
 import org.apache.groovy.json.internal.FastStringUtils;
-import org.apache.groovy.util.Maps;
 import org.codehaus.groovy.control.CompilationFailedException;
 import org.codehaus.groovy.control.CompilerConfiguration;
-import org.codehaus.groovy.control.customizers.ASTTransformationCustomizer;
 import org.codehaus.groovy.control.customizers.SecureASTCustomizer;
 import org.codehaus.groovy.runtime.InvokerHelper;
 import org.kohsuke.groovy.sandbox.GroovyInterceptor;
@@ -44,6 +37,12 @@
  * @author GraviteeSource Team
  */
 public class SecuredGroovyShell {
+
+    /**
+     * Number of hours to keep compiled script in cache after the last time it was accessed.
+     */
+    private static final int CODE_CACHE_EXPIRATION_HOURS = 1;
+
     static {
         // Do not change this block of code which is required to work with groovy 2.5 and the classloader used
         // to load services
@@ -53,11 +52,13 @@ public class SecuredGroovyShell {
         Thread.currentThread().setContextClassLoader(loader);
     }
 
-    private GroovyShell groovyShell;
-    private ConcurrentMap<String, Class<?>> sources = new ConcurrentHashMap<>();
-    private GroovyInterceptor groovyInterceptor;
+    private final GroovyShell groovyShell;
+    private final Cache<String, Class<?>> sources;
+    private final GroovyInterceptor groovyInterceptor;
 
     public SecuredGroovyShell() {
+        this.sources = CacheBuilder.newBuilder().expireAfterAccess(Duration.ofHours(CODE_CACHE_EXPIRATION_HOURS)).build();
+
         CompilerConfiguration conf = new CompilerConfiguration();
 
         // Add Kohsuke's sandbox transformer which will delegate calls to SecuredInterceptor.
@@ -101,12 +102,22 @@ public <T> T evaluate(String script, Binding binding) {
     private Class<?> getOrCreate(String script) throws CompilationFailedException {
         String key = Sha1.sha1(script);
 
-        return sources.computeIfAbsent(
-            key,
-            s -> {
-                GroovyCodeSource gcs = new GroovyCodeSource(script, key, GroovyShell.DEFAULT_CODE_BASE);
-                return groovyShell.getClassLoader().parseClass(gcs, true);
+        try {
+            return sources.get(
+                key,
+                () -> {
+                    GroovyCodeSource gcs = new GroovyCodeSource(script, key, GroovyShell.DEFAULT_CODE_BASE);
+                    return groovyShell.getClassLoader().parseClass(gcs, true);
+                }
+            );
+        } catch (Exception e) {
+            final Throwable cause = e.getCause();
+            if (cause instanceof CompilationFailedException) {
+                throw (CompilationFailedException) cause;
+            } else if (cause instanceof SecurityException) {
+                throw (SecurityException) cause;
             }
-        );
+            throw new RuntimeException("Unable to compile script", e);
+        }
     }
 }
diff --git a/src/main/java/io/gravitee/policy/groovy/sandbox/SecuredResolver.java b/src/main/java/io/gravitee/policy/groovy/sandbox/SecuredResolver.java
index c8c7d06..383c8cb 100644
--- a/src/main/java/io/gravitee/policy/groovy/sandbox/SecuredResolver.java
+++ b/src/main/java/io/gravitee/policy/groovy/sandbox/SecuredResolver.java
@@ -107,13 +107,19 @@ public class SecuredResolver {
     private final Map<Class<?>, List<Method>> methodsByTypeAndSuperTypes;
     private final Map<String, Boolean> resolved;
 
-    public static void initialize(@Nullable Environment environment) {
-        loadWhitelist(environment);
-        INSTANCE = new SecuredResolver();
+    public static synchronized void initialize(@Nullable Environment environment) {
+        if (!isInitialized()) {
+            loadWhitelist(environment);
+            INSTANCE = new SecuredResolver();
+        }
+    }
+
+    public static synchronized boolean isInitialized() {
+        return INSTANCE != null;
     }
 
-    public static void destroy() {
-        if (INSTANCE != null) {
+    public static synchronized void destroy() {
+        if (isInitialized()) {
             methodsByType.clear();
             fieldsByType.clear();
             constructorsByType.clear();
@@ -123,7 +129,7 @@ public static void destroy() {
     }
 
     public static SecuredResolver getInstance() {
-        if (INSTANCE == null) {
+        if (!isInitialized()) {
             initialize(null);
         }
 
diff --git a/src/main/java/io/gravitee/policy/groovy/utils/Sha1.java b/src/main/java/io/gravitee/policy/groovy/utils/Sha1.java
index cb69ab7..cc0fee2 100644
--- a/src/main/java/io/gravitee/policy/groovy/utils/Sha1.java
+++ b/src/main/java/io/gravitee/policy/groovy/utils/Sha1.java
@@ -41,13 +41,12 @@ private static String convertToHex(byte[] data) {
     public static String sha1(String text) {
         try {
             MessageDigest md = MessageDigest.getInstance("SHA-1");
-            byte[] sha1hash = new byte[40];
+            byte[] sha1hash;
             md.update(text.getBytes("UTF-8"), 0, text.length());
             sha1hash = md.digest();
             return convertToHex(sha1hash);
         } catch (Exception ex) {
-            ex.printStackTrace();
-            return null;
+            throw new RuntimeException(ex);
         }
     }
 }