2022-05-24 use of spiel

Preface

SpEL（Spring Expression Language,Spring Expression language ） No need to follow Spring binding , It can be used alone , Make some expressions for strings , It can be used in many places ; First explain SpEL The basic use of , Then post a current application scenario .

SpEL

Based on using

SpEL It is mainly divided into three interfaces

• Expression expression
• ExpressionParser Expression parsing
• EvaluationContext Evaluate context

Next is around these three Interface Implementation class , Post some basic usage

1. Operation string

	public static void main(String[] args) {
    
        SpelExpressionParser parser = new SpelExpressionParser();
        Expression exp1 = parser.parseExpression("'hello,world!!'");
        String exp1Str = (String)exp1.getValue();
        System.out.println(exp1Str);
    }

Output ：hello,world!!

SpEL The really powerful places are not all here

public static void main(String[] args) {
    
        SpelExpressionParser parser = new SpelExpressionParser();
        Expression exp1 = parser.parseExpression("'hello,world!!'.length");
        Object value = exp1.getValue();
        System.out.println(value);
}

Output ：13

It can be in Expression Execute logical code in string

2. Arithmetic calculation

public static void main(String[] args) {
    
        SpelExpressionParser parser = new SpelExpressionParser();
        Expression exp1 = parser.parseExpression("'hello,world!!'.length + 10");
        Object value = exp1.getValue();
        System.out.println(value);
}

Output ：23

3. Logical operations

public static void main(String[] args) {
    
        SpelExpressionParser parser = new SpelExpressionParser();
        Expression exp1 = parser.parseExpression("'hello,world!!'.length + 10");
        Object value = exp1.getValue();
        System.out.println(value);
}

4. Variable

public static void main(String[] args) {
    
        SpelExpressionParser parser = new SpelExpressionParser();
        Expression exp1 = parser.parseExpression("#user.username");
        StandardEvaluationContext context = new StandardEvaluationContext();
        User user = new User();
        user.setUsername("zsl");
        user.setPassword("a123456");
        context.setVariable("user", user);

        Object value = exp1.getValue(context, String.class);
        System.out.println(value);
}

Output ：zsl

Store variables in EvaluationContext In the variables of the interface implementation class , Use Expression Expression processing back Context The value in ; You can also operate on multiple variables ：

public static void main(String[] args) {
    
        SpelExpressionParser parser = new SpelExpressionParser();
        Expression exp1 = parser.parseExpression("#user.username + #user.password");
        StandardEvaluationContext context = new StandardEvaluationContext();
        User user = new User();
        user.setUsername("zsl");
        user.setPassword("a123456");
        context.setVariable("user", user);

        Object value = exp1.getValue(context, String.class);
        System.out.println(value);
}

Output ：zsla123456

application

It is troublesome to process the operation log in the code, and you need to call log.info() Method , Can combine SpEL And annotations to collect logs

@LogRecord(content = "' User name from {#oldUsername}  It is amended as follows {#request.username}")
public Object update(UserRequest request) {
    
    UserDao.update(request);
}

Use Aop Intercepted by @LogRecord The method of decoration , Collect content and process , End use SpEL To analyze ;

Later, we will use SpEL Realize the improvement of log items and submit them to Github in , Welcome to your attention ~
https://github.com/zsl0/costom_box

Inheritance relationships

ExpressionParser

Expression parser implementation ：

Portfolio model ：

Realization ：

Expression

Expression implementation ：

EvaluationContext

Evaluate context implementation ：

Description of other classes

ExpressionKey：AnnotatedElementKey And expressions

AnnotatedElementKey： Deposit method And the target

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