diff --git a/core/src/main/java/org/elasticsearch/action/admin/cluster/node/info/PluginsAndModules.java b/core/src/main/java/org/elasticsearch/action/admin/cluster/node/info/PluginsAndModules.java
index 3a9658ea816..206dd262ed8 100644
--- a/core/src/main/java/org/elasticsearch/action/admin/cluster/node/info/PluginsAndModules.java
+++ b/core/src/main/java/org/elasticsearch/action/admin/cluster/node/info/PluginsAndModules.java
@@ -44,30 +44,14 @@ public class PluginsAndModules implements Writeable, ToXContent {
     }
 
     public PluginsAndModules(StreamInput in) throws IOException {
-        int pluginsSize = in.readInt();
-        List<PluginInfo> plugins = new ArrayList<>(pluginsSize);
-        for (int i = 0; i < pluginsSize; i++) {
-            plugins.add(new PluginInfo(in));
-        }
-        this.plugins = Collections.unmodifiableList(plugins);
-        int modulesSize = in.readInt();
-        List<PluginInfo> modules = new ArrayList<>(modulesSize);
-        for (int i = 0; i < modulesSize; i++) {
-            modules.add(new PluginInfo(in));
-        }
-        this.modules = Collections.unmodifiableList(modules);
+        this.plugins = Collections.unmodifiableList(in.readList(PluginInfo::new));
+        this.modules = Collections.unmodifiableList(in.readList(PluginInfo::new));
     }
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeInt(plugins.size());
-        for (PluginInfo plugin : getPluginInfos()) {
-            plugin.writeTo(out);
-        }
-        out.writeInt(modules.size());
-        for (PluginInfo module : getModuleInfos()) {
-            module.writeTo(out);
-        }
+        out.writeList(plugins);
+        out.writeList(modules);
     }
 
     /**
diff --git a/core/src/main/java/org/elasticsearch/monitor/jvm/JvmInfo.java b/core/src/main/java/org/elasticsearch/monitor/jvm/JvmInfo.java
index d370a06cdc8..ca0bb4f3e80 100644
--- a/core/src/main/java/org/elasticsearch/monitor/jvm/JvmInfo.java
+++ b/core/src/main/java/org/elasticsearch/monitor/jvm/JvmInfo.java
@@ -36,7 +36,6 @@ import java.lang.management.PlatformManagedObject;
 import java.lang.management.RuntimeMXBean;
 import java.lang.reflect.Method;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -226,11 +225,7 @@ public class JvmInfo implements Writeable, ToXContent {
         }
         bootClassPath = in.readString();
         classPath = in.readString();
-        systemProperties = new HashMap<>();
-        int size = in.readInt();
-        for (int i = 0; i < size; i++) {
-            systemProperties.put(in.readString(), in.readString());
-        }
+        systemProperties = in.readMap(StreamInput::readString, StreamInput::readString);
         mem = new Mem(in);
         gcCollectors = in.readStringArray();
         memoryPools = in.readStringArray();
@@ -257,7 +252,7 @@ public class JvmInfo implements Writeable, ToXContent {
         }
         out.writeString(bootClassPath);
         out.writeString(classPath);
-        out.writeInt(systemProperties.size());
+        out.writeVInt(this.systemProperties.size());
         for (Map.Entry<String, String> entry : systemProperties.entrySet()) {
             out.writeString(entry.getKey());
             out.writeString(entry.getValue());
diff --git a/core/src/main/java/org/elasticsearch/threadpool/ThreadPoolInfo.java b/core/src/main/java/org/elasticsearch/threadpool/ThreadPoolInfo.java
index d30d872691c..70c0f2c9598 100644
--- a/core/src/main/java/org/elasticsearch/threadpool/ThreadPoolInfo.java
+++ b/core/src/main/java/org/elasticsearch/threadpool/ThreadPoolInfo.java
@@ -26,7 +26,6 @@ import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
@@ -40,20 +39,12 @@ public class ThreadPoolInfo implements Writeable, Iterable<ThreadPool.Info>, ToX
     }
 
     public ThreadPoolInfo(StreamInput in) throws IOException {
-        int size = in.readVInt();
-        List<ThreadPool.Info> infos = new ArrayList<>(size);
-        for (int i = 0; i < size; i++) {
-            infos.add(new ThreadPool.Info(in));
-        }
-        this.infos = Collections.unmodifiableList(infos);
+        this.infos = Collections.unmodifiableList(in.readList(ThreadPool.Info::new));
     }
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeVInt(infos.size());
-        for (ThreadPool.Info info : infos) {
-            info.writeTo(out);
-        }
+        out.writeList(infos);
     }
 
     @Override