Steps to make you app and database work with utf8mb4 characters in order to accept emojis. It's based on a webapp using Maven+Hibernate+Spring+Jetty+MySQL

AppDelegate.m

//
//  AppDelegate.m
//
//  Created by andre.michels on 12/3/13.
//

#import "AppDelegate.h"
#import "NetworkAvailabilityUtils.h"

@implementation TableViewHistoryAppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    
    //Initializing Network Observer
    [NetworkAvailabilityUtils instance];
    
    return YES;
}

BaseNetworkRequest.h

//
//  BaseNetworkRequest.h
//
//  Created by Paulo Almeida on 12/9/13.
//

#import <Foundation/Foundation.h>

@protocol BaseNetworkDelegate <NSObject>

-(void) sucessOnRequest:(NSDictionary*) jsonArray AndIdentifier:(NSString*) identifier;
-(void) errorOnRequest:(NSString*) identifier;
-(void) noConnectivity;

@end

@interface BaseNetworkRequest : NSObject

#pragma Properties

@property (nonatomic, strong) NSURL *url;
@property (nonatomic,strong) id <BaseNetworkDelegate> delegate;
@property (nonatomic,strong) NSString* identifier;

#pragma Methods

-(void) startGetRequest;
-(void) startPostRequest:(NSData*)postBody;
-(void) startPostMultipartDataRequest:(NSDictionary *)postParameters;
@end

BaseNetworkRequest.m

//
//  BaseNetworkRequest.m
//  now
//
//  Created by Paulo Almeida on 12/9/13.
//  Copyright (c) 2013 Loducca. All rights reserved.
//

#import "BaseNetworkRequest.h"
#import "NetworkAvailabilityUtils.h"

@implementation BaseNetworkRequest

-(void) startGetRequest
{
    if(![NetworkAvailabilityUtils isConnected]){
        
        [self.delegate noConnectivity];
        
        return;
        
    }
    
    NSURLRequest *request = [NSURLRequest requestWithURL:[self url]];
    
    [NSURLConnection sendAsynchronousRequest:request queue: [NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
     {
         if(error)
         {
             [self.delegate errorOnRequest:[self identifier]];
             
         }
         else
         {
             if([data length]>0)
             {
                 NSError *error = nil;
                 NSDictionary *jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
                 
                 if (error != nil) {
                     [self.delegate errorOnRequest:[self identifier]];
                 }
                 else {
                     NSNumber *code = [jsonArray objectForKey:@"code"];
                     if([code intValue] == 0)
                     {
                         //NSLog(@"Array: %@", jsonArray);
                         [self.delegate sucessOnRequest:jsonArray AndIdentifier:[self identifier]];
                     }
                     else
                     {
                         [self.delegate errorOnRequest:[self identifier]];
                     }
                     
                 }
                 
                 
             }
             else
             {
                 [self.delegate errorOnRequest:[self identifier]];
             }
             
         }

         
     }];

}

-(void) startPostRequest:(NSData *)postBody
{
    if(![NetworkAvailabilityUtils isConnected]){
       
        [self.delegate noConnectivity];
       
        return;

    }
    
    NSMutableURLRequest *postRequest = [NSMutableURLRequest requestWithURL:[self url]];
    
    [postRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    
    [postRequest setValue:[NSString
                       stringWithFormat:@"%lu", (unsigned long)[postBody length]]
   forHTTPHeaderField:@"Content-length"];
    
    [postRequest setHTTPMethod:@"POST"];
    [postRequest setHTTPBody:postBody];
    
    
    [NSURLConnection sendAsynchronousRequest:postRequest queue: [NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
     {
         if(error)
         {
             [self.delegate errorOnRequest:[self identifier]];

         }
         else
         {
             if([data length]>0)
             {
                 //NSLog(@"Return  from Server: %@",[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]);
                 NSError *error = nil;
                 NSDictionary *jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
                 
                 if (error != nil) {
                     [self.delegate errorOnRequest:[self identifier]];
                 }
                 else {
                     NSNumber *code = [jsonArray objectForKey:@"code"];
                     if([code intValue] == 0)
                     {
                         NSLog(@"Array: %@", jsonArray);
                         [self.delegate sucessOnRequest:jsonArray AndIdentifier:[self identifier]];
                     }
                     else
                     {
                         [self.delegate errorOnRequest:[self identifier]];
                     }
                     
                 }
             }
             else
             {
                 [self.delegate errorOnRequest:[self identifier]];
             }
             
         }
     }];
}

-(void) startPostMultipartDataRequest:(NSDictionary *)postParameters
{
    if(![NetworkAvailabilityUtils isConnected]){
        
        [self.delegate noConnectivity];
        
        return;
        
    }
    
    NSMutableURLRequest *postRequest = [NSMutableURLRequest requestWithURL:[self url]];
    
    NSString *boundary = @"---------------------------14737809831466499882746641449";
    NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@",boundary];
    
    [postRequest setValue:contentType forHTTPHeaderField:@"Content-Type"];
    
    NSMutableData *postbody = [NSMutableData data];

    
    NSEnumerator *enumerator = [postParameters keyEnumerator];
    id key;
    while ((key = [enumerator nextObject])) {
        NSObject *tmp = [postParameters objectForKey:key];
        
        if([tmp isKindOfClass:[NSData class]]){
            [postbody appendData:[[NSString stringWithFormat:@"--%@\r\n",boundary] dataUsingEncoding:NSUTF8StringEncoding]];
            [postbody appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"; filename=\"%@.jpg\"\r\n", key,key] dataUsingEncoding:NSUTF8StringEncoding]];
            
            [postbody appendData:[[NSString stringWithFormat:@"Content-Type: application/octet-stream\r\n\r\n"] dataUsingEncoding:NSUTF8StringEncoding]];
            [postbody appendData:[NSData dataWithData:[postParameters objectForKey:key]]];
            [postbody appendData:[[NSString stringWithFormat:@"\r\n"] dataUsingEncoding:NSUTF8StringEncoding]];
        }else{
            [postbody appendData:[[NSString stringWithFormat:@"--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
            [postbody appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"\r\n\r\n", key] dataUsingEncoding:NSUTF8StringEncoding]];
            [postbody appendData:[[NSString stringWithFormat:@"%@\r\n", [postParameters objectForKey:key]] dataUsingEncoding:NSUTF8StringEncoding]];
        }
    }
    [postbody appendData:[[NSString stringWithFormat:@"--%@--\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
    
    [postRequest setHTTPMethod:@"POST"];
    [postRequest setHTTPBody:postbody];
    
    NSString *postLength = [NSString stringWithFormat:@"%d", (int)[postbody length]];
    [postRequest setValue:postLength forHTTPHeaderField:@"Content-Length"];
    
    
    [NSURLConnection sendAsynchronousRequest:postRequest queue: [NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
     {
         if(error)
         {
             [self.delegate errorOnRequest:[self identifier]];
             
         }
         else
         {
             if([data length]>0)
             {
                 NSError *error = nil;
                 NSDictionary *jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
                 
                 if (error != nil) {
                     [self.delegate errorOnRequest:[self identifier]];
                 }
                 else {
                     NSNumber *code = [jsonArray objectForKey:@"code"];
                     if([code intValue] == 0)
                     {
                         //NSLog(@"Array: %@", jsonArray);
                         [self.delegate sucessOnRequest:jsonArray AndIdentifier:[self identifier]];
                     }
                     else
                     {
                         [self.delegate errorOnRequest:[self identifier]];
                     }
                     
                 }
                 
                 
             }
             else
             {
                 [self.delegate errorOnRequest:[self identifier]];
             }
             
         }
         
         
     }];
    
    
}

@end

Comment.java

package com.github.gist.utf8mb4.domain;

import org.hibernate.annotations.SQLDelete;
import org.hibernate.annotations.Where;

import javax.validation.Valid;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
import javax.persistence.*;
import java.util.Date;

@Entity
@SQLDelete(sql = "UPDATE Comment SET dateRemoval = CURRENT_TIMESTAMP() WHERE id = ?")
@Where(clause = "dateRemoval is null")
public class Comment {
	private static final long serialVersionUID = 1L;
	
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Integer id;

	@ManyToOne(targetEntity = User.class)
	@Valid
	@NotNull
	private User user;
	
	@Column(length = 400, nullable = false)
	@NotNull
	@Size(min = 1, max = 400)
	private String text;

  	@Column(insertable = true, updatable = false)
  	@Temporal(TemporalType.TIMESTAMP)
  	private Date dateInsertion;
  
  	@Column(insertable = false, updatable = false)
  	@Temporal(TemporalType.TIMESTAMP)
  	private Date dateRemoval;
  
  	public Comment() {
  	}
  
	//Getters and Setters
}

InsertComment.m

NSString *postData = [NSString stringWithFormat:@"text=%@",_homeTextComment.text ];

BaseNetworkRequest *insertCommentRequest = [[BaseNetworkRequest alloc] init];
[insertCommentRequest setDelegate:self];
[insertCommentRequest setUrl:[NSURL URLWithString:[Constants COMMENT_INSERT_SERVICE]]];
[insertCommentRequest setIdentifier:@"insertCommentRequest"];

[insertCommentRequest startPostRequest:[postData dataUsingEncoding:NSUTF8StringEncoding]];

jetty-env.xml

<!-- 
  This file must be place within src/main/webapp/WEB-INF/jetty-env.xml
-->

<?xml version="1.0"?>
<Configure id='wac' class="org.eclipse.jetty.webapp.WebAppContext">

    <New id="jdbc/ds" class="org.eclipse.jetty.plus.jndi.Resource">
        <Arg>jdbc/now</Arg>
        <Arg>
            <New class="org.apache.commons.dbcp.BasicDataSource">
                <Set name="driverClassName">com.mysql.jdbc.Driver</Set>
                <Set name="url">jdbc:mysql://<yourhost>:3306/<db>
                </Set>
                <Set name="username">yourusername</Set>
                <Set name="password">yourpass</Set>
                <Set name="initialSize">10</Set>
                <Set name="maxActive">20</Set>
                <Set name="maxIdle">15</Set>
            </New>
        </Arg>
    </New>
</Configure>

my.cnf

#Add the following lines to your my.cnf file

[mysqld]

character-set-client-handshake = FALSE
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci

NetworkAvailabilityUtils.h

//
//  NetworkAvailabilityUtils.h
//
//  Created by Paulo Almeida on 12/10/13.
//

#import <Foundation/Foundation.h>
#import "Reachability.h"

@interface NetworkAvailabilityUtils : NSObject
@property (nonatomic,strong) Reachability *reachability ;

+(NetworkAvailabilityUtils*) instance;
+(BOOL) isConnected;
@end

NetworkAvailabilityUtils.m

//
//  NetworkAvailabilityUtils.m
//
//  Created by Paulo Almeida on 12/10/13.
//

#import "NetworkAvailabilityUtils.h"


@implementation NetworkAvailabilityUtils

static NetworkAvailabilityUtils *instance;

static bool isConnected;

+(NetworkAvailabilityUtils*) instance
{
    if(instance == NULL)
    {
        instance = [[self alloc]init];
    }
    return instance;
}

+(BOOL) isConnected
{
    return isConnected;
}

- (id)init {
    if ( (self = [super init]) ) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(networkChanged:) name:kReachabilityChangedNotification object:nil];
        
        _reachability = [Reachability reachabilityForInternetConnection];
        [_reachability startNotifier];
        
        //Perform a first check in order to get the actual scenario
        [self networkChanged:nil];
    }
    return self;
}


- (void)networkChanged:(NSNotification *)notification
{
    
    NetworkStatus remoteHostStatus = [_reachability currentReachabilityStatus];
    
    if(remoteHostStatus == NotReachable)
    {
        NSLog(@"not reachable");
        isConnected = NO;
    }
    else if (remoteHostStatus == ReachableViaWiFi)
    {
        NSLog(@"wifi");
        isConnected = YES;
    }
    else if (remoteHostStatus == ReachableViaWWAN)
    {
        NSLog(@"carrier");
        isConnected = YES;
    }
}

@end

pom.xml

<!-- 
  To run this application using command line: mvn clean compile package jetty:run -DskipTests -Pjetty
-->


<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    
    <groupId>com.github.gist</groupId>
    <artifactId>utf8mb4example</artifactId>
    <packaging>war</packaging>
    <version>1.0</version>

    <properties>
    		<configuration.source>1.6</configuration.source>
    		<configuration.target>1.6</configuration.target>
    		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    		<org.springframework.version>3.1.1.RELEASE</org.springframework.version>
        <com.google.code.gson.gson.version>1.7.1</com.google.code.gson.gson.version>
	  </properties>

    <dependencies>
        <!-- Jackson JSON Mapper -->
        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-mapper-asl</artifactId>
            <version>1.5.3</version>
        </dependency>

        <!-- Servlet API -->
        <dependency>
            <groupId>org.mortbay.jetty</groupId>
            <artifactId>servlet-api-2.5</artifactId>
            <version>6.1.11</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.0</version>
            <scope>provided</scope>
        </dependency>

        <!-- JSON to Java Converter -->
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>${com.google.code.gson.gson.version}</version>
        </dependency>

        <!-- Spring framework -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-core</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-web</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-config</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>

        <!-- JUnit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
        <!-- JSTL -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.1.2</version>
        </dependency>
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>

    </dependencies>


    <profiles>
        <profile>
            <id>jetty</id>
            <dependencies>
                <dependency>
                    <groupId>commons-dbcp</groupId>
                    <artifactId>commons-dbcp</artifactId>
                    <version>1.2</version>
                </dependency>
                <dependency>
                    <groupId>mysql</groupId>
                    <artifactId>mysql-connector-java</artifactId>
                    <version>5.1.28</version>
                </dependency>
            </dependencies>
            <build>
                <plugins>
                    <plugin>
                        <groupId>org.eclipse.jetty</groupId>
                        <artifactId>jetty-maven-plugin</artifactId>
                        <version>9.1.0.M0</version>
                        <configuration>
                            <webAppConfig>
                                <contextPath>/</contextPath>
                            </webAppConfig>
                            <systemProperties>
                                <systemProperty>
                                    <name>org.mortbay.util.URI.charset</name>
                                    <value>UTF-8</value>
                                </systemProperty>
                            </systemProperties>
                        </configuration>
                    </plugin>
                </plugins>
            </build>
        </profile>
    </profiles>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.0.2</version>
                <configuration>
                    <source>${configuration.source}</source>
                    <target>${configuration.target}</target>
                </configuration>
            </plugin>
        </plugins>

        <finalName>${project.artifactId}</finalName>
    </build>

</project>

scriptAltertable.sql

ALTER DATABASE db
  DEFAULT CHARACTER SET utf8mb4
  DEFAULT COLLATE utf8mb4_unicode_ci;

ALTER TABLE Comment CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci, MODIFY COLUMN text varchar(400) CHARACTER SET utf8mb4 ;

web.xml

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0">
	<display-name>WebApp</display-name>

	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>/WEB-INF/security-context.xml</param-value>
	</context-param>

	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>
	<listener>
        <listener-class>
            org.springframework.web.context.request.RequestContextListener
        </listener-class>
    </listener>
    
    <!-- Filter Encoding -->
    <filter>
        <filter-name>encoding-filter</filter-name>
        <filter-class>
            org.springframework.web.filter.CharacterEncodingFilter
        </filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
        <init-param>
        <param-name>forceEncoding</param-name>
        <param-value>true</param-value>
        </init-param>
    </filter>

    <filter-mapping>
        <filter-name>encoding-filter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

	<!-- Filter Config -->
	<filter>
		<filter-name>springSecurityFilterChain</filter-name>
		<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
	</filter>

	<!-- Filter Mappings -->
	<filter-mapping>
		<filter-name>springSecurityFilterChain</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

	<servlet>
		<servlet-name>spring</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>spring</servlet-name>
		<url-pattern>*.action</url-pattern>
	</servlet-mapping>
	
	<resource-ref>
		<description>DataSource</description>
		<res-ref-name>jdbc/ds</res-ref-name>
		<res-type>javax.sql.DataSource</res-type>
		<res-auth>Container</res-auth>
	</resource-ref>

</web-app>