[Java] 設計模式：代碼形狀 lambda表達式的一個應用 Code Shape 模式這裡介紹一個模式：Code Shape。沒聽過，不要緊，我剛剛纔起的名字。作用在應用程式的開發中，我們一般會使用多層架構。在這種情況下，每一層的方法往往會呈現相同的代碼結構。這裡稱之為層的代碼形狀。 ...

[Java] Design Pattern：Code Shape - manage your code shape

Code Shape Design Pattern

Here I will introduce a design pattern: Code Shape。
It's fine that you never heard that, I just created it.

Usage

In the enterprise application development, in most cases, we adopt multiple layers architectures.
Methods in each layer tend to present the same code structure. Here we name it as code shape.
For example, in the database access layer, writing methods would have following code:

Get the database connection.
Begin a transaction.
Write database.
Commit the transaction.
When there is an exception, rollback the transaction.

Beside, some times, architects hope to add some infrastructure functions, e.g.

Unified processing authority authentication.
Unified handling exceptions.
Logging.
Profiling for performance.
Logging method parameters.

So, the design pattern code shape implements the above requirements by using Java lambda expressions
Provide a flexible way to manage every method shape in a layer.

Code Demonstrate

This article presents a code demonstrate to implement following features:

Before calling a method, write a log
Log method parameters
After calling the method, write a log
If applicable, log the return value
When there is an exception, log the exception

Prerequisites

About Java 8 Lambda Expressions, please see here.

Java provides java.util.function.Consumer and java.util.function.Function, to benefit us a convenience way to use lambda expressions.

Consumer can be used by non-return methods, and Function can be used by methods which have return.
Unfortunately, they only support one argument.
Therefore, if need, we have to write interfaces to support multiple arguments.
Here are samples to support tow input arguments:

ConsumerTwo

@FunctionalInterface
public interface ConsumerTwo<T, T2> {
    public void accept(T t, T2 t2);
}

FunctionTwo

@FunctionalInterface
public interface FunctionTwo<T, T2, R> {
    public R apply(T t, T2 t2);
}

Annotation FunctionalInterface indicates this is a function interface, only one method is defined inside.

Main class code

The main class calls 3 samples:
The first sample: it is a method without return.
The second sample: it is a method without return, but always throw an exception.
The third sample: it is a method with return.

Code:

Main.java

public class Main {
    public static void main(String[] args) {
        
        pattern.CodeShapeSample br = new pattern.CodeShapeSample();

        // call business rule one
        br.businessRuleOne("Jack", "is man");

        // call business rule two, will get an exception
        try {
            br.businessRuleTwoThrowException("Tom", "is woman");
        }
        catch (Exception e) {}

        // call business rule three which has a return.
        String value = br.businessRuleThree("Mary", "is woman");
    }
}

Code Shape Design Patter Code

CodeShapeSample

package pattern;

import java.text.MessageFormat;
import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;

public class CodeShapeSample {
    
    /*
     * This is a consumer sample
     */
    public void businessRuleOne(final String name, final String value) {
        
        CodeShapePattern.consumerShape.accept((o) -> {
            // here is business rule logical
            System.out.println(name + " " + value);
        }, Arrays.asList(name, value));
    }
    
    /*
     * This is a consumer with exception sample
     */
    public void businessRuleTwoThrowException(final String name, final String value) {
        
        CodeShapePattern.consumerShape.accept((o) -> {
            // here is business rule logical
            throw new RuntimeException("failure!");
        }, Arrays.asList(name, value));
    }
    
    /*
     * This is a function sample
     */
    public String businessRuleThree(final String name, final String value) {
        
        return CodeShapePattern.<String>getFunctionShape().apply((o) -> {
            // here is business rule logical
            return name + " " + value;
        }, Arrays.asList(name, value));
    }
}

CodeShapePattern

package pattern;

import java.text.MessageFormat;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;

public class CodeShapePattern {

    public static ConsumerTwo<Consumer<Object>, List<Object>> consumerShape = (body, params) -> 
    {
        StackTraceElement caller = new Exception().getStackTrace()[2];
        String method = caller.getClassName() + "#" + caller.getMethodName();
        try {
            System.out.println("");
            System.out.println("========");
            System.out.println(MessageFormat.format("start method ''{0}''", method));
            if (params != null) {
                for(Object param : params) {
                    System.out.println(MessageFormat.format("parameter : ''{0}''", param.toString()));
                }
            }
            
            System.out.println("---- start body ----");
            body.accept(null);
            System.out.println("---- end body ----");
            System.out.println(MessageFormat.format("end method ''{0}''", method));
        }
        catch (Exception e) {
            System.out.println(MessageFormat.format("error method ''{0}'': {1}", method, e.getMessage()));
            throw e;
        }
    };
    
    public static <R> FunctionTwo<Function<Object, R>, List<Object>, R> getFunctionShape() {
        FunctionTwo<Function<Object, R>, List<Object>, R> function = (body, params) -> 
        {
            R ret = null;
            StackTraceElement caller = new Exception().getStackTrace()[2];
            String method = caller.getClassName() + "#" + caller.getMethodName();
            try {
                System.out.println("");
                System.out.println("========");
                System.out.println(MessageFormat.format("start method ''{0}''", method));
                if (params != null) {
                    for(Object param : params) {
                        System.out.println(MessageFormat.format("parameter : ''{0}''", param.toString()));
                    }
                }
                
                System.out.println("---- start body ----");
                ret = body.apply(null);
                System.out.println("---- end body ----");
                System.out.println(MessageFormat.format("end method ''{0}'', return ''{1}''", method, ret.toString()));
            }
            catch (Exception e) {
                System.out.println(MessageFormat.format("error method ''{0}'': {1}", method, e.getMessage()));
                throw e;
            }
            return ret;
        };
        
        return function;
    }
}

Explanation 1：using Consumer

OK. All code is presented, let's explain them.

Business Rule Code
As this business rule method does not return any thing, so I use CodeShapePattern.consumerShape.
There are 2 input parameters.: business rule logical and the method's parameter values.

    /*
     * This is a consumer sample
     */
    public void businessRuleOne(final String name, final String value) {
        
        CodeShapePattern.consumerShape.accept((o) -> {
            // here is business rule logical
            System.out.println(name + " " + value);
        }, Arrays.asList(name, value));
    }

Code Shape Design Patter Code - Consumer
We can see it, the consumerShape is a static variable that implements unified functions.
This consumerShape uses a nested Consumer.
The Consumer inside is the business rule logical., In business rule methods, you can write any code what you want.
BTW, the input parameter is useless, we may define a ConsumerZero class to simplify the code.

    public static ConsumerTwo<Consumer<Object>, List<Object>> consumerShape = (body, params) -> 
    {
        StackTraceElement caller = new Exception().getStackTrace()[2];
        String method = caller.getClassName() + "#" + caller.getMethodName();
        try {
            System.out.println("");
            System.out.println("========");
            System.out.println(MessageFormat.format("start method ''{0}''", method));
            if (params != null) {
                for(Object param : params) {
                    System.out.println(MessageFormat.format("parameter : ''{0}''", param.toString()));
                }
            }
            
            System.out.println("---- start body ----");
            body.accept(null);
            System.out.println("---- end body ----");
            System.out.println(MessageFormat.format("end method ''{0}''", method));
        }
        catch (Exception e) {
            System.out.println(MessageFormat.format("error method ''{0}'': {1}", method, e.getMessage()));
            throw e;
        }
    };

Less code version:

    public static ConsumerTwo<Consumer<Object>, List<Object>> consumerShape = (body, params) -> 
    {
        try {
            body.accept(null);
        }
        catch (Exception e) {
            throw e;
        }
    };

Explanation 2: Using Function

Business Rule Layer method
As this business rule layer method has return, we use CodeShapePattern.<R>getFunctionShape() inside.
getFunctionShape() is a generic method, the generic type is the return type of the business rule method.
There are 2 parameters:
The first: business rule logical, with return.
The second: parameters of the business rule method, for internal use.

    /*
     * This is a function sample
     */
    public String businessRuleThree(final String name, final String value) {
        
        return CodeShapePattern.<String>getFunctionShape().apply((o) -> {
            // here is business rule logical
            return name + " " + value;
        }, Arrays.asList(name, value));
    }

Code Shape Design Patter - Function
Different as the consumerShape, getFunctionShape is a static generic method that implements unified functions.
This getFunctionShape uses a nested Function.
The Function inside is the business rule logical., In business rule methods, you can write any code what you want.
BTW, the input parameter is useless, we may define a FunctionZero class to simplify the code.

    public static <R> FunctionTwo<Function<Object, R>, List<Object>, R> getFunctionShape() {
        FunctionTwo<Function<Object, R>, List<Object>, R> function = (body, params) -> 
        {
            R ret = null;
            StackTraceElement caller = new Exception().getStackTrace()[2];
            String method = caller.getClassName() + "#" + caller.getMethodName();
            try {
                System.out.println("");
                System.out.println("========");
                System.out.println(MessageFormat.format("start method ''{0}''", method));
                if (params != null) {
                    for(Object param : params) {
                        System.out.println(MessageFormat.format("parameter : ''{0}''", param.toString()));
                    }
                }
                
                System.out.println("---- start body ----");
                ret = body.apply(null);
                System.out.println("---- end body ----");
                System.out.println(MessageFormat.format("end method ''{0}'', return ''{1}''", method, ret.toString()));
            }
            catch (Exception e) {
                System.out.println(MessageFormat.format("error method ''{0}'': {1}", method, e.getMessage()));
                throw e;
            }
            return ret;
        };
        
        return function;
    }