Java--Map与实体类对象之间互转

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