解析Spring源码（1）--ClassPathResource("xxx.xml");

首先看看我们是如何使用Spring的

    public static void main(String[] args) {
        BeanFactory bf=new XmlBeanFactory(new ClassPathResource("bean_test.xml"));

        HelloWorldService hw=(HelloWorldService) bf.getBean("helloWorldService");
        hw.hello();
    }
1
2
3
4
5
6

查看源码（简化版）：
首先看看类的一些关系，

public class ClassPathResource extends AbstractFileResolvingResource

public abstract class AbstractResource implements Resource

public class ClassPathResource extends AbstractFileResolvingResource {

    private final String path;

    private ClassLoader classLoader;

    private Class<?> clazz;


    /**
     * 构造函数，只有一个参数path="xxx.xml"
     */
    public ClassPathResource(String path) {
        this(path, (ClassLoader) null);
    }

    /**
     * 构造函数，
     * 创建实例对象，并初始化参数path,classLoader
     */
    public ClassPathResource(String path, ClassLoader classLoader) {
        this.path = pathToUse;//pathToUse="bean_test.xml";
        this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

对于获取classLoader：ClassUtils.getDefaultClassLoader()

    /**
     * 返回类加载器
     */
    public static ClassLoader getDefaultClassLoader() {
        ClassLoader cl = null;
            //获得类加载器
            cl = Thread.currentThread().getContextClassLoader();
        return cl;
    }
1
2
3
4
5
6
7
8
9
10

至此我们创建了一个ClassPathResource实例对象，并初始化了path=”bean_test.xml”，classLoader=Thread.currentThread().getContextClassLoader()参数

原版源码：

public class ClassPathResource extends AbstractFileResolvingResource {

    private final String path;

    private ClassLoader classLoader;

    private Class<?> clazz;


    /**
     * 构造函数，只有一个参数path="xxx.xml"
     * Create a new {@code ClassPathResource} for {@code ClassLoader} usage.
     * A leading slash will be removed, as the ClassLoader resource access
     * methods will not accept it.
     * <p>The thread context class loader will be used for
     * loading the resource.
     * @param path the absolute path within the class path
     * @see java.lang.ClassLoader#getResourceAsStream(String)
     * @see org.springframework.util.ClassUtils#getDefaultClassLoader()
     */
    public ClassPathResource(String path) {
        this(path, (ClassLoader) null);
    }

    /**
     * 构造函数，
     * 创建实例对象，并初始化参数path,classLoader
     * Create a new {@code ClassPathResource} for {@code ClassLoader} usage.
     * A leading slash will be removed, as the ClassLoader resource access
     * methods will not accept it.
     * @param path the absolute path within the classpath
     * @param classLoader the class loader to load the resource with,
     * or {@code null} for the thread context class loader
     * @see ClassLoader#getResourceAsStream(String)
     */
    public ClassPathResource(String path, ClassLoader classLoader) {
        //Assert,StringUtils暂时不管
        Assert.notNull(path, "Path must not be null");
        String pathToUse = StringUtils.cleanPath(path);
        if (pathToUse.startsWith("/")) {
            pathToUse = pathToUse.substring(1);
        }
        this.path = pathToUse;//pathToUse="bean_test.xml";
        this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45

    /**
     * 返回类加载器
     * Return the default ClassLoader to use: typically the thread context
     * ClassLoader, if available; the ClassLoader that loaded the ClassUtils
     * class will be used as fallback.
     * <p>Call this method if you intend to use the thread context ClassLoader
     * in a scenario where you clearly prefer a non-null ClassLoader reference:
     * for example, for class path resource loading (but not necessarily for
     * {@code Class.forName}, which accepts a {@code null} ClassLoader
     * reference as well).
     * @return the default ClassLoader (only {@code null} if even the system
     * ClassLoader isn't accessible)
     * @see Thread#getContextClassLoader()
     * @see ClassLoader#getSystemClassLoader()
     */
    public static ClassLoader getDefaultClassLoader() {
        ClassLoader cl = null;
        try {
            //获得类加载器
            cl = Thread.currentThread().getContextClassLoader();
        }
        catch (Throwable ex) {
            // Cannot access thread context ClassLoader - falling back...
        }
        if (cl == null) {
            // No thread context class loader -> use class loader of this class.
            cl = ClassUtils.class.getClassLoader();
            if (cl == null) {
                // getClassLoader() returning null indicates the bootstrap ClassLoader
                try {
                    cl = ClassLoader.getSystemClassLoader();
                }
                catch (Throwable ex) {
                    // Cannot access system ClassLoader - oh well, maybe the caller can live with null...
                }
            }
        }
        return cl;
    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40

至此我们创建了一个ClassPathResource实例对象，并初始化了path=”bean_test.xml”，classLoader=Thread.currentThread().getContextClassLoader()参数