问题描述
apache的BeanUtils工具集中用来把map对象转换为java对象的BeanUtils#populate方法会因为单例的原因其转换器Converter被相互污染覆盖问题
maven依赖
<dependency>
<groupId>commons-beanutils</groupId>
<artifactId>commons-beanutils</artifactId>
<version>1.9.4</version>
</dependency>
方法源码
public static void populate(final Object bean, final Map<String, ? extends Object> properties)
throws IllegalAccessException, InvocationTargetException {
// 源码此处获取的是单例对象
BeanUtilsBean.getInstance().populate(bean, properties);
}
测试场景
场景一
map不存在属性时
测试代码
/**
* map没有age属性
*/
public static void test1() throws Exception {
DemoObj fromObj = new DemoObj();
Map<String, Object> map = Maps.newHashMap();
map.put("name", "张三");
BeanUtils.populate(fromObj, map);
System.out.println(Thread.currentThread().getName() + "：没有age属性，转换器不生效："+ JsonUtil.toStr(fromObj));
}
输出结果
main：没有age属性，转换器不生效：{"age":null,"name":"张三"}
场景二
map存在age属性，自带的转换器默认值为0
测试代码
/**
* map存在age属性，自带的转换器默认值为0
*/
public static void test2() throws Exception {
DemoObj fromObj = new DemoObj();
Map<String, Object> map = Maps.newHashMap();
map.put("name", "李四");
map.put("age", null);
BeanUtils.populate(fromObj, map);
System.out.println(Thread.currentThread().getName() +"：自带的转换器默认值为0："+JsonUtil.toStr(fromObj));
}
输出结果
main：自带的转换器默认值为0：{"age":0,"name":"李四"}
场景三
静态代码块注入自定义转换器，默认值设置为null
测试代码
static {
ConvertUtils.register(new IntegerConverter(null), Integer.class);
}
public static void test2() throws Exception {
DemoObj fromObj = new DemoObj();
Map<String, Object> map = Maps.newHashMap();
map.put("name", "李四");
map.put("age", null);
BeanUtils.populate(fromObj, map);
System.out.println(Thread.currentThread().getName() +"：转换器默认值为："+JsonUtil.toStr(fromObj));
}
输出结果
main：转换器默认值为：{"age":null,"name":"李四"}
场景四
在场景三的基础上，我们增加了一个转换器重新注册的函数调用，该函数会重置转换器对象
转换器重置的源代码
public static void deregister() {
ConvertUtilsBean.getInstance().deregister();
}
// 获取的依旧是单例对象
protected static ConvertUtilsBean getInstance() {
return BeanUtilsBean.getInstance().getConvertUtils();
}
public void deregister() {
converters.clear();
registerPrimitives(false);
registerStandard(false, false);
registerOther(true);
registerArrays(false, 0);
register(BigDecimal.class, new BigDecimalConverter());
register(BigInteger.class, new BigIntegerConverter());
}
测试代码
static {
ConvertUtils.register(new IntegerConverter(null), Integer.class);
}
public static void test2() throws Exception {
DemoObj fromObj = new DemoObj();
Map<String, Object> map = Maps.newHashMap();
map.put("name", "李四");
map.put("age", null);
BeanUtils.populate(fromObj, map);
System.out.println(Thread.currentThread().getName() +"：转换器默认值为："+JsonUtil.toStr(fromObj));
}
public static void test3() throws Exception {
DemoObj fromObj = new DemoObj();
Map<String, Object> map = Maps.newHashMap();
map.put("name", "王五");
map.put("age", null);
BeanUtils.populate(fromObj, map);
System.out.println(Thread.currentThread().getName() + "：age被赋值默认值："+ JsonUtil.toStr(fromObj));
// 重置转换器
ConvertUtils.deregister();
}
public static void main(String[] args) throws Exception {
new Thread(()-> {
try {
// 睡眠，等test2先跑完
Thread.sleep(1000);
test2();
} catch (Exception e) {
throw new RuntimeException(e);
}
}).start();
new Thread(()-> {
try {
test3();
} catch (Exception e) {
throw new RuntimeException(e);
}
}).start();
}
输出结果
当前线程执行时，转换器还是静态代码块所注册的默认值为null的转换器，但是在test3执行完后会重置单例的转换器对象
Thread-2：age被赋值默认值：{"age":null,"name":"王五"}
所以线程睡眠结束后再执行转换时，发现转换器已被污染，转换的属性默认值非预期值
Thread-1：转换器默认值为：{"age":0,"name":"李四"}
场景五
在场景四的基础上重新创建一个单例对象，并且该单例提前注册一个自定义默认值为null的的转换器
新增类
public class CustBeanUtils {
private static final BeanUtilsBean beanUtilsBean;
public CustBeanUtils() {
}
public static void populate(Object bean, Map<String, ? extends Object> properties) throws Exception {
beanUtilsBean.populate(bean, properties);
}
static {
ConvertUtilsBean convertUtilsBean = new ConvertUtilsBean();
convertUtilsBean.register(new IntegerConverter(null), Integer.class);
beanUtilsBean = new BeanUtilsBean(convertUtilsBean, new PropertyUtilsBean());
}
}
测试代码
static {
ConvertUtils.register(new IntegerConverter(null), Integer.class);
}
public static void test2() throws Exception {
DemoObj fromObj = new DemoObj();
Map<String, Object> map = Maps.newHashMap();
map.put("name", "李四");
map.put("age", null);
BeanUtils.populate(fromObj, map);
System.out.println(Thread.currentThread().getName() +"：转换器默认值为："+JsonUtil.toStr(fromObj));
}
public static void test3() throws Exception {
DemoObj fromObj = new DemoObj();
Map<String, Object> map = Maps.newHashMap();
map.put("name", "王五");
map.put("age", null);
BeanUtils.populate(fromObj, map);
System.out.println(Thread.currentThread().getName() + "：age被赋值默认值："+ JsonUtil.toStr(fromObj));
// 重置转换器
ConvertUtils.deregister();
}
public static void test4() throws Exception {
DemoObj fromObj = new DemoObj();
Map<String, Object> map = Maps.newHashMap();
map.put("name", "赵六");
map.put("age", null);
CustBeanUtils.populate(fromObj, map);
System.out.println(Thread.currentThread().getName() + "：CustBeanUtils 新建了一个BeanUtilsBean，不受其影响，age也不会被赋值默认值0："+ JsonUtil.toStr(fromObj));
}
public static void main(String[] args) throws Exception {
new Thread(()-> {
try {
Thread.sleep(1000);
test2();
} catch (Exception e) {
throw new RuntimeException(e);
}
}).start();
new Thread(()-> {
try {
test3();
} catch (Exception e) {
throw new RuntimeException(e);
}
}).start();
new Thread(()-> {
try {
Thread.sleep(2000);
test4();
} catch (Exception e) {
throw new RuntimeException(e);
}
}).start();
}
输出结果
线程2执行时，转换器还是静态代码块所注册的默认值为null的转换器，但是在test3执行完后会重置单例的转换器对象
Thread-2：age被赋值默认值：{"age":null,"name":"王五"}
所以线程1睡眠结束后再执行转换时，发现转换器已被污染，转换的属性默认值非预期值
Thread-1：转换器默认值为：{"age":0,"name":"李四"}
由于线程3用的是一个新的单例对象，所以其转换结果并不受原生的工具集中转换器重置的函数所影响
Thread-3：CustBeanUtils 新建了一个BeanUtilsBean，不受其影响，age也不会被赋值默认值0：{"age":null,"name":"赵六"}