Java--Map与实体类对象之间互转

野性酷女 2023-10-03 13:35 28阅读 0赞

#### 一、json转换 ####

依赖阿里的FastJSon，用到的主要jar包：fastjson-1.2.54.jar

1、maven引入

<dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>fastjson</artifactId>
        <version>1.2.54</version>
    </dependency>

2、类引入

import com.alibaba.fastjson.JSON;

3、转换

简单使用

//map转对象
    User user = JSON.parseObject(JSON.toJSONString(map), User.class);
    
    //对象转map
    Map<String, Object> map = JSONObject.parseObject(JSONObject.toJSONString(user));

封装提取方法

//map转java对象
    public static Object mapToObject(Map<String, Object> map, Class<?> bean) throws Exception {
      String jsonStr = JSONObject.toJSONString(map);
      return JSONObject.parseObject(jsonStr, Bean.Class);
    }
      
    //java对象转map
    public static Map<String, Object> objectToMap(Object obj) {
      String jsonStr = JSONObject.toJSONString(obj);
      return JSONObject.parseObject(jsonStr, Map.Class);
    }

#### 二、**使用org.apache.commons.beanutils转换** ####

用到的主要jar包：commons-beanutils-1.9.3.jar

//map转java对象
    public static Object mapToObject(Map<String, Object> map, Class<?> beanClass)
      throws Exception {
     if (map == null) {
      return null;
     }
     Object obj = beanClass.newInstance();
     BeanUtils.populate(obj, map);
     return obj;
     }
     
    //java对象转map
    public static Map<?, ?> objectToMap(Object obj) {
     if (obj == null)
      return null;
     return new BeanMap(obj);
     }

在使用该方法进行java对象转map时，可能会发生以下错误：

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/collections/Transformer
     at java.lang.ClassLoader.defineClass1(Native Method)
     at java.lang.ClassLoader.defineClass(ClassLoader.java:621)
     at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
     at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
     at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
     at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
     at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
     at org.apache.commons.beanutils.BeanMap.createTypeTransformers(BeanMap.java:132)
     at org.apache.commons.beanutils.BeanMap.<clinit>(BeanMap.java:68)
     at com.example2.pojo.PojoToMap.objectToMap(PojoToMap.java:23)
     at com.example2.pojo.PojoToMap.main(PojoToMap.java:16)
    Caused by: java.lang.ClassNotFoundException: org.apache.commons.collections.Transformer
     ...

从报错信息上看，是缺少了org.apache.commons.collections.Transformer类，网上下载commons-collections-3.2.1.jar包，引入后，重新执行，成功

#### 三、**使用Introspector转换** ####

//map转java对象
    public static Object mapToObject(Map<String, Object> map, Class<?> beanClass) throws Exception {
        if (map == null)
          return null;
        Object obj = beanClass.newInstance();
        BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass());
        PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
        for (PropertyDescriptor property : propertyDescriptors) {
          Method setter = property.getWriteMethod();
          if (setter != null) {
            setter.invoke(obj, map.get(property.getName()));
          }
        }
        return obj;
      }
     
    //java对象转map
    public static Map<String, Object> objectToMap(Object obj) throws Exception {
     if (obj == null) {
     return null;
     }
     Map<String, Object> map = new HashMap<String, Object>();
     BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass());
     PropertyDescriptor[] propertyDescriptors = beanInfo
      .getPropertyDescriptors();
     for (PropertyDescriptor property : propertyDescriptors) {
     String key = property.getName();
     if (key.compareToIgnoreCase("class") == 0) {
      continue;
     }
     Method getter = property.getReadMethod();
     Object value = getter != null ? getter.invoke(obj) : null;
     map.put(key, value);
     }
     return map;
    }

#### 四、**使用reflect转换** ####

//map转java对象
    public static Object mapToObject(Map<String, Object> map, Class<?> beanClass) throws Exception {
        if (map == null) {
          return null;
        }
        Object object = beanClass.newInstance();
        Field[] fields = beanClass.getDeclaredFields();
        for (Field field : fields) {
          int mod = field.getModifiers();
          if (Modifier.isFinal(mod) || Modifier.isStatic(mod)) {
            continue;
          }
          field.setAccessible(true);
          field.set(object, map.get(field.getName()));
        }
        return object;
      }
     
    //java对象转map
    public static Map<String, Object> objectToMap(Object obj) throws Exception {
     if (obj == null) {
     return null;
     }
     Map<String, Object> map = new HashMap<String, Object>();
     Field[] declaredFields = obj.getClass().getDeclaredFields();
     for (Field field : declaredFields) {
     field.setAccessible(true);
     map.put(field.getName(), field.get(obj));
     }
     return map;
    }

#### 五、**使用net.sf.cglib.beans.BeanMap转换** ####

用到的主要jar包：cglib-2.2.2.jar

//map转java对象
    public static Object mapToObject(Map<String, Object> map, Class<?> beanClass) throws Exception {
      Object object = beanClass.newInstance();
      BeanMap beanMap = BeanMap.create(object);
      beanMap.putAll(map);
      return object;
    }
     
    //java对象转map
    public static Map<String, Object> objectToMap(Object obj) {
      Map<String, Object> map = Maps.newHashMap();
      if (obj != null) {
        BeanMap beanMap = BeanMap.create(obj);
        for (Object key : beanMap.keySet()) {
          map.put(key + "", beanMap.get(key));
        }
      }
      return map;
    }

在使用本方法进行map转java对象时，可能会发生以下错误：

Exception in thread "main" java.lang.NoClassDefFoundError: org/objectweb/asm/Type
     at net.sf.cglib.core.TypeUtils.parseType(TypeUtils.java:184)
     at net.sf.cglib.core.KeyFactory.<clinit>(KeyFactory.java:66)
     at net.sf.cglib.beans.BeanMap$Generator.<clinit>(BeanMap.java:64)
     at net.sf.cglib.beans.BeanMap.create(BeanMap.java:56)
     at com.example2.pojo.MapToPojo.mapToBean(MapToPojo.java:27)
     at com.example2.pojo.MapToPojo.main(MapToPojo.java:18)
    Caused by: java.lang.ClassNotFoundException: org.objectweb.asm.Type
     at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
     at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
     ... 6 more

从错误信息上看，是缺少了org.objectweb.asm.Type类，从网上下载了com.springsource.org.objectweb.asm-3.2.0.jar包，引入后，再次执行，成功