Spring實現(xiàn)泛型注入的示例詳解
1.Spring泛型注入
創(chuàng)建一個抽象泛型類BaseDao,有參數(shù)化類型T
public abstract class BaseDao<T> { public abstract void eat(); }
每種動物有不同的行為,貓、狗
public class Cat { } public class Dog { }
分別繼承BaseDao實現(xiàn)不同的行為
@Repository public class CatDao extends BaseDao<Cat> { @Override public void eat() { System.out.println("cat eat...."); } }
@Repository public class DogDao extends BaseDao<Dog> { @Override public void eat() { System.out.println("dog eat...."); } }
接著創(chuàng)建一個抽象業(yè)務(wù)類,也有參數(shù)化類型T。
注意:此處不能使用@Resource注入,會找到多個BaseDao類型的bean,無法確認(rèn)注入哪一個bean會報錯
需要使用@Autowired注入,它有根據(jù)泛型參數(shù)匹配的邏輯,會一個個去匹配
public abstract class BaseService<T> { @Autowired private BaseDao<T> baseDao; protected void eat() { baseDao.eat(); } }
子類繼承BaseService指定參數(shù)化類型實現(xiàn)注入相應(yīng)的BaseDao
@Service public class CatService extends BaseService<Cat> { }
@Service public class DogService extends BaseService<Dog> { }
代碼目錄
測試
@Configuration @ComponentScan(value = "com.monian.test.generic") public class GenericConfig { }
public class GenericTests { public static void main(String[] args) { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(); applicationContext.register(GenericConfig.class); applicationContext.refresh(); DogService dogService = applicationContext.getBean(DogService.class); CatService catService = applicationContext.getBean(CatService.class); dogService.eat(); catService.eat(); } }
結(jié)果輸出,成功注入相應(yīng)的BaseDao
2. 關(guān)于java泛型有四種Type
GenericArrayType泛型數(shù)組類型
public class GenericArrayTypeTest { public static class TestClass<S> { // 泛型數(shù)組 private List<String>[] lists; // 泛型數(shù)組 private S[] ss; private String[] s; } public static void main(String[] args) { Class cl = TestClass.class; for (Field field : cl.getDeclaredFields()) { System.out.println("filed's name:" + field.getName()); Type genericType = field.getGenericType(); System.out.println("Is it genericArrayType:" + (genericType instanceof GenericArrayType)); if (genericType instanceof GenericArrayType) { GenericArrayType genericArrayType = (GenericArrayType) genericType; System.out.println(genericArrayType.getTypeName()); Type genericComponentType = genericArrayType.getGenericComponentType(); System.out.println(genericComponentType); } System.out.println(); } } }
result:
filed's name:lists
Is it genericArrayType:true
java.util.List<java.lang.String>[]
java.util.List<java.lang.String>
filed's name:ss
Is it genericArrayType:true
S[]
S
filed's name:s
Is it genericArrayType:false
ParameterizedType參數(shù)化類型
public class ParameterizedTypeTest { public static abstract class Test<T> { public abstract void test(T t); } public static class TestClass<T extends Number> extends Test<Integer> { private List<T> tList; private List<? extends Number> list; private Map<String, Integer> map; @Override public void test(Integer o) { } } public static void main(String[] args) { TestClass<Integer> tt = new TestClass<>(); Class cl = tt.getClass(); Type genericSuperclass = cl.getGenericSuperclass(); assert genericSuperclass instanceof ParameterizedType; ParameterizedType parameterizedType1 = (ParameterizedType) genericSuperclass; System.out.println(parameterizedType1.getActualTypeArguments()[0]); for (Field field : cl.getDeclaredFields()) { System.out.println("field's name:" + field.getName()); Type genericType = field.getGenericType(); System.out.println("Is it ParameterizedType:" + (genericType instanceof ParameterizedType)); if (genericType instanceof ParameterizedType) { ParameterizedType parameterizedType = (ParameterizedType) genericType; for (Type type : parameterizedType.getActualTypeArguments()) { System.out.println("actualType:" + type); System.out.println(type.getTypeName()); } } System.out.println(); } } }
result:
class java.lang.Integer
field's name:tList
Is it ParameterizedType:true
actualType:T
T
field's name:list
Is it ParameterizedType:true
actualType:? extends java.lang.Number
? extends java.lang.Number
field's name:map
Is it ParameterizedType:true
actualType:class java.lang.String
java.lang.String
actualType:class java.lang.Integer
java.lang.Integer
TypeVariable 類型變量
public class TypeVariableTest { public static class TestClass<S extends Number, T> { private Map<S, T> map; } public static void main(String[] args) throws Exception { Class cl = TestClass.class; Field field = cl.getDeclaredField("map"); Type genericType = field.getGenericType(); ParameterizedType parameterizedType = (ParameterizedType) genericType; for (Type type : parameterizedType.getActualTypeArguments()) { TypeVariable typeVariable = (TypeVariable) type; // 類型變量名 System.out.println(typeVariable.getName()); // 變量上邊界 Type[] bounds = typeVariable.getBounds(); System.out.println(Arrays.toString(bounds)); } } }
result:
S
[class java.lang.Number]
T
[class java.lang.Object]
WildcardType 通配符類型
public class WildcardTypeTest { public static class TestClass { private List<? extends Number> lists; private Set<?> sets; private Map<? extends Number, ? super String> map; } public static void main(String[] args) { Class cl = TestClass.class; for (Field field : cl.getDeclaredFields()) { System.out.println("filed's name:" + field.getName()); Type genericType = field.getGenericType(); ParameterizedType parameterizedType = (ParameterizedType) genericType; for (Type type : parameterizedType.getActualTypeArguments()) { // 通配符類型 WildcardType wildcardType = (WildcardType) type; System.out.println(wildcardType.getTypeName()); // 上邊界 System.out.println("上邊界" + Arrays.toString(wildcardType.getUpperBounds())); // 下邊界 System.out.println("下邊界" + Arrays.toString(wildcardType.getLowerBounds())); } System.out.println(); } } }
result:
filed's name:lists
? extends java.lang.Number
上邊界[class java.lang.Number]
下邊界[]
filed's name:sets
?
上邊界[class java.lang.Object]
下邊界[]
filed's name:map
? extends java.lang.Number
上邊界[class java.lang.Number]
下邊界[]
? super java.lang.String
上邊界[class java.lang.Object]
下邊界[class java.lang.String]
注:spring對泛型的解析主要是在ResolvableType類,掌握上述的基本知識后可以去閱讀下相關(guān)源碼
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