对于 Base<F,T>这样的带泛型参数的抽象类，如何在类初始化时得到F,T对应的类型？
Guava TypeToken是一个功能强大的泛型解析工具。可以很简单的实际这个需求。
如下一行代码就可以完成解析：
Type resolved = new TypeToken<F>(getClass()) {}.getType();
在执行 TypeToken(Class<?> declaringClass)构造方法时已经完成了对F类型参数的解析，保存到runtimeType字段。如下为 TypeToken(Class<?> declaringClass)构造方法的代码：
/*** 这里declaringClass必须为声明类型变量的类*/protected TypeToken(Class<?> declaringClass) {Type captured = super.capture();if (captured instanceof Class) {this.runtimeType = captured;} else {/*** 非Class的泛型变量，则调用 resolveType 方法解析 T 为具体参数 * 由declaringClass创建的TypeToken对象完整保存了类型变量到实际类型的对应表，* 所以resolveType方法就是通过查表得到对应具体类型*/this.runtimeType = of(declaringClass).resolveType(captured).runtimeType;}}
调用示例
import static org.junit.Assert.*;import java.lang.reflect.Type;
import java.util.Date;
import java.util.List;
import java.util.Map;import org.junit.FixMethodOrder;
import org.junit.Test;
import org.junit.runners.MethodSorters;import com.google.common.reflect.TypeToken;/*** Guava TypeToken 解析类型变量(TypeVariable)测试* @author l0km*/
@FixMethodOrder(MethodSorters.NAME_ASCENDING)
public class ResolveTypeTest {@SuppressWarnings("serial")@Testpublic void test() {Base<String,Date> base = new Base<String,Date>() {};assertEquals(String.class, base.inputType);assertEquals(Date.class, base.outputType);Sub1<Date> sub1 = new Sub1<Date>() {};assertEquals(String.class, sub1.inputType);assertEquals(Date.class, sub1.outputType);Sub2<Map<Integer,Type>> sub2 = new Sub2<Map<Integer,Type>>() {};assertEquals(new TypeToken<Map<Integer,Type>>() {}.getType(), sub2.inputType);assertEquals(String.class, sub2.outputType);Sub3<List<Date>> sub3 = new Sub3<List<Date>>() {};assertEquals(String.class, sub3.inputType);assertEquals(new TypeToken<List<Date>>() {}.getType(), sub3.outputType);Sub4<int[]> sub4 = new Sub4<int[]>() {};assertEquals(int[].class, sub4.inputType);assertEquals(String.class, sub4.outputType);}public static abstract class Base<F,T>{final Type inputType;final Type outputType;@SuppressWarnings("serial")protected Base(){inputType = new TypeToken<F>(getClass()) {}.getType();System.out.printf("inputType: %s\n",inputType);outputType = new TypeToken<T>(getClass()) {}.getType();System.out.printf("outputType: %s\n",outputType);}}public static abstract class Sub1<T> extends Base<String,T>{}public static abstract class Sub2<F> extends Base<F,String>{}public static abstract class Sub3<T> extends Sub1<T>{}public static abstract class Sub4<F> extends Sub2<F>{}}
