How is Java reflection used for metaprogramming?

The Java reflection mechanism provides metaprogramming capabilities and can dynamically inspect and modify class information. Read class information: Get class name, method and field information. Get methods: Get the declared methods and call them. Modify classes: Dynamically change the behavior of a class by modifying fields. Practical case: Dynamically generate JSON: Use reflection to dynamically generate a JSON representation of an object.

Metaprogramming usage of Java reflection mechanism

Java reflection mechanism enables developers to inspect and modify class information at runtime . This provides a strong foundation for metaprogramming, which is generating and modifying code based on class information at runtime. The following is an example of how Java reflection can be used for metaprogramming:

Read class information

Class<?> clazz = Person.class;
System.out.println(clazz.getName()); // 输出：Person

Get method

Method[] methods = clazz.getDeclaredMethods();
for (Method method : methods) {
    System.out.println(method.getName()); // 输出：getName, setName, getAge, setAge
}

Execution method

Object person = clazz.newInstance(); // 创建 Person 的实例
Method setNameMethod = clazz.getMethod("setName", String.class);
setNameMethod.invoke(person, "John Doe"); // 调用 setName 方法

Modify class

Field ageField = clazz.getDeclaredField("age");
ageField.setAccessible(true);
ageField.setInt(person, 30); // 将字段 age 设置为 30

Actual case: dynamically generate JSON

Assume that there are A Person class, we need to convert its object into a JSON string. We can generate JSON dynamically using Java reflection:

JSONArray jsonArray = new JSONArray();
for (Method method : methods) {
    String methodName = method.getName();
    if (methodName.startsWith("get")) {
        String propertyName = methodName.substring(3);
        Object propertyValue = method.invoke(person);
        jsonArray.put(propertyName, propertyValue);
    }
}
System.out.println(jsonArray.toJSONString()); // 输出：{"name":"John Doe","age":30}

By integrating Java reflection into metaprogramming, we can dynamically process and modify classes. This makes it possible to write dynamic, versatile and scalable code.

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