////  User.h//  dss////  Created by ST on 16/6/7.//  Copyright © 2016年 ST. All rights reserved.//#import 
    
     @interface User : NSObject@property (nonatomic, strong) NSString *id; //@property (nonatomic, strong) NSString *nums; //@end
    

////  User.m//  dss////  Created by ST on 16/6/7.//  Copyright © 2016年 ST. All rights reserved.//#import "User.h"@implementation User@end

////  ViewController.m//  dss////  Created by ST on 16/6/7.//  Copyright © 2016年 ST. All rights reserved.//#import "ViewController.h"#import "NSObject+MJKeyValue.h"#import "User.h"@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];        // 1.定义一个字典数组    User *user1 = [[User alloc] init];    user1.id = @"Jack";    user1.nums = @"11";        User *user2 = [[User alloc] init];    user2.id = @"Rose";    user2.nums = @"22";        User *user3 = [[User alloc] init];    user3.id = @"lucy";    user3.nums = @"33";        NSArray *userArray = @[user1, user2, user3];        // Model array -> JSON array    NSArray *dictArray = [User mj_keyValuesArrayWithObjectArray:userArray];       NSError *error;    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dictArray options:NSJSONWritingPrettyPrinted error:&error];    NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];    NSLog(@"%@",jsonString);}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end/输出的是一个json字符串：2016-06-08 11:40:28.560 dss[4515:3986811] [  {    "id" : "Jack",    "nums" : "11"  },  {    "id" : "Rose",    "nums" : "22"  },  {    "id" : "lucy",    "nums" : "33"  }]