如果你曾經使用過 Spring, 那你已經配過 包掃描路徑吧，那包掃描是怎么實現的呢？讓我們自己寫個包掃描
上篇文章中介紹了使用 File 遍歷的方式去進行包掃描，這篇主要補充一下jar包的掃描方式，在我們的項目中一般都會去依賴一些其他jar 包，
比如添加 guava 依賴
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>28.2-jre</version>
</dependency>
我們再次運行上次的測試用例
@Test
public void testGetPackageAllClasses() throws IOException, ClassNotFoundException {
ClassScanner scanner = new ClassScanner("com.google.common.cache", true, null, null);
Set<Class<?>> packageAllClasses = scanner.doScanAllClasses();
packageAllClasses.forEach(it -> {
System.out.println(it.getName());
});
}
什么都沒有輸出
依賴的 Jar
基于Java 的反射機制，我們很容易根據 class 去創建一個實例對象，但如果我們根本不知道某個包下有多少對象時，我們應該怎么做呢？
在使用Spring框架時，會根據包掃描路徑來找到所有的 class, 并將其實例化后存入容器中。
在我們的項目中也會遇到這樣的場景，比如某個包為 org.example.plugins, 這個里面放著所有的插件，為了不每次增減插件都要手動修改代碼，我們可能會想到用掃描的方式去動態獲知 org.example.plugins 到底有多少 class, 當然應用場景很有很多
思路
既然知道是采用了 jar , 那我們使用遍歷 jar 的方式去處理一下
JarFile jar = ((JarURLConnection) url.openConnection()).getJarFile();
// 遍歷jar包中的元素
Enumeration<JarEntry> entries = jar.entries();
while (entries.hasMoreElements()) {
JarEntry entry = entries.nextElement();
String name = entry.getName();
}
這里獲取的name 格式為 com/google/common/cache/Cache.class 是不是和上篇的文件路徑很像呀, 這里可以通過對 name 進行操作獲取包名和 class
// 獲取包名
String jarPackageName = name.substring(0, name.lastIndexOf('/')).replace("/", ".");
// 獲取 class 路徑, 這樣就能通過類加載進行加載了
String className = name.replace('/', '.');
className = className.substring(0, className.length() - 6);
完整代碼
private void doScanPackageClassesByJar(String basePackage, URL url, Set<Class<?>> classes)
throws IOException, ClassNotFoundException {
// 包名
String packageName = basePackage;
// 獲取文件路徑
String basePackageFilePath = packageName.replace('.', '/');
// 轉為jar包
JarFile jar = ((JarURLConnection) url.openConnection()).getJarFile();
// 遍歷jar包中的元素
Enumeration<JarEntry> entries = jar.entries();
while (entries.hasMoreElements()) {
JarEntry entry = entries.nextElement();
String name = entry.getName();
// 如果路徑不一致，或者是目錄，則繼續
if (!name.startsWith(basePackageFilePath) || entry.isDirectory()) {
continue;
}
// 判斷是否遞歸搜索子包
if (!recursive && name.lastIndexOf('/') != basePackageFilePath.length()) {
continue;
}
if (packagePredicate != null) {
String jarPackageName = name.substring(0, name.lastIndexOf('/')).replace("/", ".");
if (!packagePredicate.test(jarPackageName)) {
continue;
}
}
// 判定是否符合過濾條件
String className = name.replace('/', '.');
className = className.substring(0, className.length() - 6);
// 用當前線程的類加載器加載類
Class<?> loadClass = Thread.currentThread().getContextClassLoader().loadClass(className);
if (classPredicate == null || classPredicate.test(loadClass)) {
classes.add(loadClass);
}
}
}
在結合上篇中 File 掃描方式就是完成的代碼了
整合后代碼
package org.example;
import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLDecoder;
import java.util.Enumeration;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.function.Predicate;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
/**
* class 掃描器
*
* @author zhangyunan
*/
public class ClassScanner {
private final String basePackage;
private final boolean recursive;
private final Predicate<String> packagePredicate;
private final Predicate<Class> classPredicate;
/**
* Instantiates a new Class scanner.
*
* @param basePackage the base package
* @param recursive 是否遞歸掃描
* @param packagePredicate the package predicate
* @param classPredicate the class predicate
*/
public ClassScanner(String basePackage, boolean recursive, Predicate<String> packagePredicate,
Predicate<Class> classPredicate) {
this.basePackage = basePackage;
this.recursive = recursive;
this.packagePredicate = packagePredicate;
this.classPredicate = classPredicate;
}
/**
* Do scan all classes set.
*
* @return the set
* @throws IOException the io exception
* @throws ClassNotFoundException the class not found exception
*/
public Set<Class<?>> doScanAllClasses() throws IOException, ClassNotFoundException {
Set<Class<?>> classes = new LinkedHashSet<Class<?>>();
String packageName = basePackage;
// 如果最后一個字符是“.”，則去掉
if (packageName.endsWith(".")) {
packageName = packageName.substring(0, packageName.lastIndexOf('.'));
}
// 將包名中的“.”換成系統文件夾的“/”
String basePackageFilePath = packageName.replace('.', '/');
Enumeration<URL> resources = Thread.currentThread().getContextClassLoader().getResources(basePackageFilePath);
while (resources.hasMoreElements()) {
URL resource = resources.nextElement();
String protocol = resource.getProtocol();
if ("file".equals(protocol)) {
String filePath = URLDecoder.decode(resource.getFile(), "UTF-8");
// 掃描文件夾中的包和類
doScanPackageClassesByFile(classes, packageName, filePath);
} else if ("jar".equals(protocol)) {
doScanPackageClassesByJar(packageName, resource, classes);
}
}
return classes;
}
private void doScanPackageClassesByJar(String basePackage, URL url, Set<Class<?>> classes)
throws IOException, ClassNotFoundException {
// 包名
String packageName = basePackage;
// 獲取文件路徑
String basePackageFilePath = packageName.replace('.', '/');
// 轉為jar包
JarFile jar = ((JarURLConnection) url.openConnection()).getJarFile();
// 遍歷jar包中的元素
Enumeration<JarEntry> entries = jar.entries();
while (entries.hasMoreElements()) {
JarEntry entry = entries.nextElement();
String name = entry.getName();
// 如果路徑不一致，或者是目錄，則繼續
if (!name.startsWith(basePackageFilePath) || entry.isDirectory()) {
continue;
}
// 判斷是否遞歸搜索子包
if (!recursive && name.lastIndexOf('/') != basePackageFilePath.length()) {
continue;
}
if (packagePredicate != null) {
String jarPackageName = name.substring(0, name.lastIndexOf('/')).replace("/", ".");
if (!packagePredicate.test(jarPackageName)) {
continue;
}
}
// 判定是否符合過濾條件
String className = name.replace('/', '.');
className = className.substring(0, className.length() - 6);
// 用當前線程的類加載器加載類
Class<?> loadClass = Thread.currentThread().getContextClassLoader().loadClass(className);
if (classPredicate == null || classPredicate.test(loadClass)) {
classes.add(loadClass);
}
}
}
/**
* 在文件夾中掃描包和類
*/
private void doScanPackageClassesByFile(Set<Class<?>> classes, String packageName, String packagePath)
throws ClassNotFoundException {
// 轉為文件
File dir = new File(packagePath);
if (!dir.exists() || !dir.isDirectory()) {
return;
}
// 列出文件，進行過濾
// 自定義文件過濾規則
File[] dirFiles = dir.listFiles((FileFilter) file -> {
String filename = file.getName();
if (file.isDirectory()) {
if (!recursive) {
return false;
}
if (packagePredicate != null) {
return packagePredicate.test(packageName + "." + filename);
}
return true;
}
return filename.endsWith(".class");
});
if (null == dirFiles) {
return;
}
for (File file : dirFiles) {
if (file.isDirectory()) {
// 如果是目錄，則遞歸
doScanPackageClassesByFile(classes, packageName + "." + file.getName(), file.getAbsolutePath());
} else {
// 用當前類加載器加載 去除 fileName 的 .class 6 位
String className = file.getName().substring(0, file.getName().length() - 6);
Class<?> loadClass = Thread.currentThread().getContextClassLoader().loadClass(packageName + '.' + className);
if (classPredicate == null || classPredicate.test(loadClass)) {
classes.add(loadClass);
}
}
}
}
}
package org.example;
import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLDecoder;
import java.util.Enumeration;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.function.Predicate;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
/**
* class 掃描器
*
* @author zhangyunan
*/
public class ClassScanner {
private final String basePackage;
private final boolean recursive;
private final Predicate<String> packagePredicate;
private final Predicate<Class> classPredicate;
/**
* Instantiates a new Class scanner.
*
* @param basePackage the base package
* @param recursive 是否遞歸掃描
* @param packagePredicate the package predicate
* @param classPredicate the class predicate
*/
public ClassScanner(String basePackage, boolean recursive, Predicate<String> packagePredicate,
Predicate<Class> classPredicate) {
this.basePackage = basePackage;
this.recursive = recursive;
this.packagePredicate = packagePredicate;
this.classPredicate = classPredicate;
}
/**
* Do scan all classes set.
*
* @return the set
* @throws IOException the io exception
* @throws ClassNotFoundException the class not found exception
*/
public Set<Class<?>> doScanAllClasses() throws IOException, ClassNotFoundException {
Set<Class<?>> classes = new LinkedHashSet<Class<?>>();
String packageName = basePackage;
// 如果最后一個字符是“.”，則去掉
if (packageName.endsWith(".")) {
packageName = packageName.substring(0, packageName.lastIndexOf('.'));
}
// 將包名中的“.”換成系統文件夾的“/”
String basePackageFilePath = packageName.replace('.', '/');
Enumeration<URL> resources = Thread.currentThread().getContextClassLoader().getResources(basePackageFilePath);
while (resources.hasMoreElements()) {
URL resource = resources.nextElement();
String protocol = resource.getProtocol();
if ("file".equals(protocol)) {
String filePath = URLDecoder.decode(resource.getFile(), "UTF-8");
// 掃描文件夾中的包和類
doScanPackageClassesByFile(classes, packageName, filePath);
} else if ("jar".equals(protocol)) {
doScanPackageClassesByJar(packageName, resource, classes);
}
}
return classes;
}
private void doScanPackageClassesByJar(String basePackage, URL url, Set<Class<?>> classes)
throws IOException, ClassNotFoundException {
// 包名
String packageName = basePackage;
// 獲取文件路徑
String basePackageFilePath = packageName.replace('.', '/');
// 轉為jar包
JarFile jar = ((JarURLConnection) url.openConnection()).getJarFile();
// 遍歷jar包中的元素
Enumeration<JarEntry> entries = jar.entries();
while (entries.hasMoreElements()) {
JarEntry entry = entries.nextElement();
String name = entry.getName();
// 如果路徑不一致，或者是目錄，則繼續
if (!name.startsWith(basePackageFilePath) || entry.isDirectory()) {
continue;
}
// 判斷是否遞歸搜索子包
if (!recursive && name.lastIndexOf('/') != basePackageFilePath.length()) {
continue;
}
if (packagePredicate != null) {
String jarPackageName = name.substring(0, name.lastIndexOf('/')).replace("/", ".");
if (!packagePredicate.test(jarPackageName)) {
continue;
}
}
// 判定是否符合過濾條件
String className = name.replace('/', '.');
className = className.substring(0, className.length() - 6);
// 用當前線程的類加載器加載類
Class<?> loadClass = Thread.currentThread().getContextClassLoader().loadClass(className);
if (classPredicate == null || classPredicate.test(loadClass)) {
classes.add(loadClass);
}
}
}
/**
* 在文件夾中掃描包和類
*/
private void doScanPackageClassesByFile(Set<Class<?>> classes, String packageName, String packagePath)
throws ClassNotFoundException {
// 轉為文件
File dir = new File(packagePath);
if (!dir.exists() || !dir.isDirectory()) {
return;
}
// 列出文件，進行過濾
// 自定義文件過濾規則
File[] dirFiles = dir.listFiles((FileFilter) file -> {
String filename = file.getName();
if (file.isDirectory()) {
if (!recursive) {
return false;
}
if (packagePredicate != null) {
return packagePredicate.test(packageName + "." + filename);
}
return true;
}
return filename.endsWith(".class");
});
if (null == dirFiles) {
return;
}
for (File file : dirFiles) {
if (file.isDirectory()) {
// 如果是目錄，則遞歸
doScanPackageClassesByFile(classes, packageName + "." + file.getName(), file.getAbsolutePath());
} else {
// 用當前類加載器加載 去除 fileName 的 .class 6 位
String className = file.getName().substring(0, file.getName().length() - 6);
Class<?> loadClass = Thread.currentThread().getContextClassLoader().loadClass(packageName + '.' + className);
if (classPredicate == null || classPredicate.test(loadClass)) {
classes.add(loadClass);
}
}
}
}
}
到此這篇關于詳解Java 包掃描實現和應用(Jar篇)的文章就介紹到這了,更多相關Java 包掃描實現和應用內容請搜索A5源碼以前的文章或繼續瀏覽下面的相關文章希望大家以后多多支持A5源碼！
