• 1 何謂 Maven shared libraries
  • 1.1 3rd party Maven library 例子
• 2 Best practices
• 3 動手寫
  • 3.1 Maven POM
  • 3.2 寫 Java code
• 4 Unit testing
  • 4.1 寫 JUnit test class
  • 4.2 Eclipse IDE JUnit code coverage
• 5 本地安裝／上載 remote repo
  • 5.1 Jacoco coverage report
• 6 喺另一個項目使用 shared library
  • 6.1 Maven dependencies
  • 6.2 寫 Java code
    • 6.2.1 檢視 shared library Java source code
    • 6.2.2 檢視 shared library Javadoc
• 7 參考資料

• Apache Commons Lang
• Apache Commons IO
• Google Guava

• 所有 public 既 Java classes 都要寫 Javadoc，因為用家可能會睇。
• 所有 public 既 Java methods 都要寫 Javadoc，因為用家可能會睇。
• 應該提供埋包含 Java source code 既 JAR 檔。
• 應該提供埋包含 Javadoc HTML 既 JAR 檔。
• 應該要寫 unit tests，最好有 full code coverage，覆蓋到所有或者大部分 branches（conditions），亦要出到 report，喺 CI/CD pipeline 平台（例如 Jenkins、GitHub Actions）上面睇到。

• src
  • /main/java
    • /code
      • MickMathUtils.java
  • /test/java
    • /code
      • MickMathUtilsTest.java
• pom.xml

1<?xml version="1.0" encoding="UTF-8"?>
2<project xmlns="http://maven.apache.org/POM/4.0.0"
3		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4		xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
5	<modelVersion>4.0.0</modelVersion>
6
7	<groupId>com.michael</groupId>
8	<artifactId>mick-math-lib</artifactId>
9	<version>1.0.0</version>
10	<packaging>jar</packaging>
11
12	<name>mick-math-lib</name>
13	<description>This is Michael's shared library for Math calculations.</description>
14
15	<properties>
16		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
17		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
18		<java.version>17</java.version>
19		<javac.source>17</javac.source>
20		<javac.target>17</javac.target>
21		<maven.compiler.target>17</maven.compiler.target>
22		<maven.compiler.source>17</maven.compiler.source>
23	</properties>
24
25	<dependencies>
26		<dependency>
27			<groupId>junit</groupId>
28			<artifactId>junit</artifactId>
29			<version>4.13.2</version>
30			<scope>test</scope>
31		</dependency>
32	</dependencies>
33
34	<build>
35		<plugins>
36			<plugin>
37				<groupId>org.apache.maven.plugins</groupId>
38				<artifactId>maven-source-plugin</artifactId>
39				<version>3.3.1</version>
40				<executions>
41					<execution>
42						<id>attach-sources</id>
43						<phase>package</phase>
44						<goals>
45							<goal>jar-no-fork</goal>
46						</goals>
47					</execution>
48				</executions>
49			</plugin>
50
51			<plugin>
52				<groupId>org.apache.maven.plugins</groupId>
53				<artifactId>maven-javadoc-plugin</artifactId>
54				<version>3.6.3</version>
55				<executions>
56					<execution>
57						<id>attach-javadoc</id>
58						<phase>package</phase>
59						<goals>
60							<goal>jar</goal>
61						</goals>
62					</execution>
63				</executions>
64			</plugin>
65
66			<plugin>
67				<groupId>org.jacoco</groupId>
68				<artifactId>jacoco-maven-plugin</artifactId>
69				<version>0.8.12</version>
70				<executions>
71					<execution>
72						<goals>
73							<goal>prepare-agent</goal>
74						</goals>
75					</execution>
76					<execution>
77						<id>jacoco-coverage</id>
78						<phase>test</phase>
79						<goals>
80							<goal>report</goal>
81						</goals>
82					</execution>
83				</executions>
84			</plugin>
85		</plugins>
86	</build>
87</project>

1package code;
2
3/**
4 * A very simple math utility class.
5 *
6 * @author Michael
7 */
8public class MickMathUtils {
9
10    /**
11     * Adds the two given values and returns the sum.
12     *
13     * @param a the fist addend (a.k.a. augend)
14     * @param b the second addend
15     * @return the sum
16     */
17    public int add(int a, int b) {
18        return a + b;
19    }
20
21    /**
22     * Divides a value by another and returns the quotient.
23     *
24     * @param a the dividend
25     * @param b the divisor
26     * @return the quotient
27     * @throws IllegalArgumentException if the divisor is zero
28     */
29    public int divide(int a, int b) throws IllegalArgumentException {
30
31        if (b == 0) {
32            throw new IllegalArgumentException("Divisor cannot be zero!");
33        }
34
35        return a / b;
36    }
37}

1package code;
2
3import org.junit.Assert;
4import org.junit.Test;
5
6public class MickMathUtilsTest {
7
8    @Test
9    public void test_add() {
10        final int sum = new MickMathUtils().add(2, 5);
11        Assert.assertEquals("Incorrect sum", 7, sum);
12    }
13
14    @Test
15    public void test_divide() {
16        final int product = new MickMathUtils().divide(10, 2);
17        Assert.assertEquals("Incorrect quotient", 5, product);
18    }
19
20    @Test
21    public void test_divide_byZero() {
22        try {
23            new MickMathUtils().divide(10, 0);
24            Assert.fail();
25        } catch (IllegalArgumentException e) {
26            // expected
27        }
28    }
29}

mvn clean test install

mvn clean test install deploy

1<parent>
2	<groupId>org.springframework.boot</groupId>
3	<artifactId>spring-boot-starter-parent</artifactId>
4	<version>3.2.5</version>
5</parent>
6
7<dependencies>
8	<dependency>
9		<groupId>org.springframework.boot</groupId>
10		<artifactId>spring-boot-starter-web</artifactId>
11	</dependency>
12
13	<dependency>
14		<groupId>com.michael</groupId>
15		<artifactId>mick-math-lib</artifactId>
16		<version>1.0.0</version>
17	</dependency>
18</dependencies>

1@RestController
2public class MyController {
3
4    @GetMapping("/add")
5    public int add(@RequestParam("a") int a, @RequestParam("b") int b) {
6        return new MickMathUtils().add(a, b);
7    }
8
9    @GetMapping("/divide")
10    public int divide(@RequestParam("a") int a, @RequestParam("b") int b) {
11        return new MickMathUtils().divide(a, b);
12    }
13}

• Maven – JaCoCo code coverage example