Chens :: Commons :: Annotations framework in the Java library apps in the Java library aries)

Cheers :: Commons :: Annotations framework in the Java library Overview: Che Core :: Commons :: Annotations is an annotation framework widely used in the Java library.Note is a method that adds metadata to the Java source code, which can be used to add some additional information to class, methods, fields, etc.Chens :: Commons :: Annotations framework provides a series of built -in annotations, which also allows developers to expand and customize annotations. Application scenario: Cheers :: Commons :: Annotations framework has a wide range of application scenarios in the Java library.Here are some common application scenarios: 1. Code generation: Developers can use annotations to mark certain code elements, and then use the compiled annotation processor to generate some additional code.For example, the method of the DAO interface can be used to generate the corresponding SQL query code through the annotation processor. 2. Configuration and constraints: The annotation can be used to provide metadata for the configuration file, so that the configuration file and the Java code have a closer relationship.By using annotations, some configuration items can be defined in the configuration file, and the annotation processor can be used to ensure the correctness and integrity of the configuration file. 3. Test: Commenting can be used to write unit testing, and the test code can be generated by the annotation processor.By using annotations, you can add some specific information to the test cases, such as the preparation of the test data, the results of expectations, etc. Technical principle: The technical principles of che. 1. Definition of annotations: The framework provides@Retention,@Target, etc. for definition of meta -annotations for defining annotations.Through meta -annotations, the life cycle and scope of the annotation can be specified. 2. Note processor: The framework uses the Java's reflection mechanism to process the annotations in the code through the annotation processor.Scan the source code when compiling or runtime, and execute the corresponding logic according to the metadata of the annotation. 3. Metal data extraction: The annotation processor obtains the relevant information of the annotation through reflection, such as the attribute value of the annotation, the code element marked marked by the annotation.Developers can implement the corresponding functions based on these metadata. Example code: Assuming we want to implement a CHE database -based database access tool class, we can configure it through Chens :: COMMONS :: Annotations.The following is the corresponding example code: @Entity(name = "employee") public class Employee { @Id private int id; @Column(name = "name") private String name; @Column(name = "age") private int age; // omit the getter and setter method } public class DBUtil { public void insert(Object obj) { // Use reflex to obtain annotation information to generate SQL query statements Class<?> clazz = obj.getClass(); if (clazz.isAnnotationPresent(Entity.class)) { Entity entity = clazz.getAnnotation(Entity.class); String tableName = entity.name(); // omit the logic of the SQL query statement System.out.println("Insert into " + tableName + " values ..."); } } } In the above example code, we define an Employee class and configure it with annotations.@ENTITY annotation is used to mark the Employee class as a physical class, and the@Column annotation is used to mark the Employee class.In the DBUTIL class, we obtain the annotation information through reflection and generate SQL query statements according to the annotation. in conclusion: Che Core :: Commons :: Annotations framework is widely used in the Java library, which can be used to achieve code generation, configuration and constraints, testing and other functions.By flexibly using the annotation and annotation processor, the readability, maintenance and scalability of the code can be improved.