- [x] I have searched the [issues](https://github.com/apache/incubator-dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] I have checked the [FAQ](https://github.com/apache/incubator-dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.5.x, 2.6.x
* Operating System version: windows 7
* Java version: jdk1.7,jdk1.8

### Steps to reproduce this issue

1. String convert to java.sql.Time
2. String convert to java.sql.Date
3. String convert to java.sql.Timestamp

### Expected Result

The Convert is successful and you can get the object of the converted type.

### Actual Result

Conversion failed.

When the interface is called by 'jmeter-plugin-dubbo', it is passed into the hashmap through a generalization call. The value in the hashmap is a Date string, and an error occurred when the server accepts a type of java.sql.timestamp |Date

If there is an exception, please attach the exception trace:

```
java.lang.RuntimeException: Failed to set pojo TestVo property timestamp value 2018-09-13 10:00:00(class java.lang.String), cause: argument type mismatch
	at com.alibaba.dubbo.common.utils.PojoUtils.realize0(PojoUtils.java:456)
	at com.alibaba.dubbo.common.utils.PojoUtils.realize(PojoUtils.java:196)
	at com.alibaba.dubbo.common.utils.PojoUtils.realize(PojoUtils.java:86)
	at com.alibaba.dubbo.rpc.filter.GenericFilter.invoke(GenericFilter.java:68)
	at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
	at com.alibaba.dubbo.rpc.filter.ClassLoaderFilter.invoke(ClassLoaderFilter.java:38)
	at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
	at com.alibaba.dubbo.rpc.filter.EchoFilter.invoke(EchoFilter.java:38)
	at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
	at com.alibaba.dubbo.rpc.protocol.dubbo.DubboProtocol$1.reply(DubboProtocol.java:103)
	at com.alibaba.dubbo.remoting.exchange.support.header.HeaderExchangeHandler.handleRequest(HeaderExchangeHandler.java:96)
	at com.alibaba.dubbo.remoting.exchange.support.header.HeaderExchangeHandler.received(HeaderExchangeHandler.java:172)
	at com.alibaba.dubbo.remoting.transport.DecodeHandler.received(DecodeHandler.java:51)
	at com.alibaba.dubbo.remoting.transport.dispatcher.ChannelEventRunnable.run(ChannelEventRunnable.java:80)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.IllegalArgumentException: argument type mismatch
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at com.alibaba.dubbo.common.utils.PojoUtils.realize0(PojoUtils.java:453)
	... 16 more
```

Phone phone1 = new Phone("86", "0571", "11223344", "001");
        Phone phone2 = new Phone("86", "0571", "11223344", "002");
        phones.add(phone1);
        phones.add(phone2);
        PersonInfo pi = new PersonInfo();
        pi.setPhones(phones);
        Phone fax = new Phone("86", "0571", "11223344", null);
        pi.setFax(fax);
        FullAddress addr = new FullAddress("CN", "zj", "1234", "Road1", "333444");
        pi.setFullAddress(addr);
        pi.setMobileNo("1122334455");
        pi.setMale(true);
        pi.setDepartment("b2b");
        pi.setHomepageUrl("www.abc.com");
        pi.setJobTitle("dev");
        pi.setName("name2");
        bigPerson.setInfoProfile(pi);
    }
    private static Child newChild(String name, int age) {
        Child result = new Child();
        result.setName(name);
        result.setAge(age);
        return result;
    }
    public void assertObject(Object data) {
        assertObject(data, null);
    }
    public void assertObject(Object data, Type type) {
        Object generalize = PojoUtils.generalize(data);
        Object realize = PojoUtils.realize(generalize, data.getClass(), type);