1 源码解析
1.1 源码解析1（jdk文件访问者的应用）
1.2 源码解析2（Spring中bean访问者的应用）
1 源码解析
1.1 源码解析1（jdk文件访问者的应用）
功能：
1 通过FileVisitor遍历文件数比较方便，比如文件夹内查找符合条件的文件，或者 按时间查找某一天创建的文件。
2 由于实现类只有一个，如果实现类不能满足我们的要求，我们可以继承实现类重写方法，或者实现fileVisitor接口，自己写方法。
接口FileVisitor：
package java.nio.file; import java.io.IOException; import java.nio.file.attribute.BasicFileAttributes; public interface FileVisitor<T> { FileVisitResult preVisitDirectory(T var1, BasicFileAttributes var2) throws IOException; FileVisitResult visitFile(T var1, BasicFileAttributes var2) throws IOException; FileVisitResult visitFileFailed(T var1, IOException var2) throws IOException; FileVisitResult postVisitDirectory(T var1, IOException var2) throws IOException; }
实现类：
package java.nio.file; import java.nio.file.attribute.BasicFileAttributes; import java.io.IOException; import java.util.Objects; public class SimpleFileVisitor<T> implements FileVisitor<T> { /** * Initializes a new instance of this class. */ protected SimpleFileVisitor() { } @Override public FileVisitResult preVisitDirectory(T dir, BasicFileAttributes attrs) throws IOException { Objects.requireNonNull(dir); Objects.requireNonNull(attrs); return FileVisitResult.CONTINUE; } @Override public FileVisitResult visitFile(T file, BasicFileAttributes attrs) throws IOException { Objects.requireNonNull(file); Objects.requireNonNull(attrs); return FileVisitResult.CONTINUE; } @Override public FileVisitResult visitFileFailed(T file, IOException exc) throws IOException { Objects.requireNonNull(file); throw exc; } @Override public FileVisitResult postVisitDirectory(T dir, IOException exc) throws IOException { Objects.requireNonNull(dir); if (exc != null) throw exc; return FileVisitResult.CONTINUE; } }
1.2 源码解析2（Spring中bean访问者的应用）
BeanDefinitionVisitor（可以遍历bean的属性，用properties来进行填充。构造器的时候委托StringValueResolver（this.resolveStringValue） 来实现）
SpringIOC要求比较复杂，该类主要是分析bean的各种数据，然后把它们进行分解。
// // Source code recreated from a .class file by IntelliJ IDEA // (powered by Fernflower decompiler) // package org.springframework.beans.factory.config; import java.util.Iterator; import java.util.LinkedHashMap; import java.util.LinkedHashSet; import java.util.List; import java.util.Map; import java.util.Set; import java.util.Map.Entry; import org.springframework.beans.MutablePropertyValues; import org.springframework.beans.PropertyValue; import org.springframework.beans.factory.config.ConstructorArgumentValues.ValueHolder; import org.springframework.util.Assert; import org.springframework.util.ObjectUtils; import org.springframework.util.StringValueResolver; public class BeanDefinitionVisitor { private StringValueResolver valueResolver; public BeanDefinitionVisitor(StringValueResolver valueResolver) { Assert.notNull(valueResolver, "StringValueResolver must not be null"); this.valueResolver = valueResolver; } protected BeanDefinitionVisitor() { } public void visitBeanDefinition(BeanDefinition beanDefinition) { this.visitParentName(beanDefinition); this.visitBeanClassName(beanDefinition); this.visitFactoryBeanName(beanDefinition); this.visitFactoryMethodName(beanDefinition); this.visitScope(beanDefinition); this.visitPropertyValues(beanDefinition.getPropertyValues()); ConstructorArgumentValues cas = beanDefinition.getConstructorArgumentValues(); this.visitIndexedArgumentValues(cas.getIndexedArgumentValues()); this.visitGenericArgumentValues(cas.getGenericArgumentValues()); } protected void visitParentName(BeanDefinition beanDefinition) { String parentName = beanDefinition.getParentName(); if (parentName != null) { String resolvedName = this.resolveStringValue(parentName); if (!parentName.equals(resolvedName)) { beanDefinition.setParentName(resolvedName); } } } protected void visitBeanClassName(BeanDefinition beanDefinition) { String beanClassName = beanDefinition.getBeanClassName(); if (beanClassName != null) { String resolvedName = this.resolveStringValue(beanClassName); if (!beanClassName.equals(resolvedName)) { beanDefinition.setBeanClassName(resolvedName); } } } protected void visitFactoryBeanName(BeanDefinition beanDefinition) { String factoryBeanName = beanDefinition.getFactoryBeanName(); if (factoryBeanName != null) { String resolvedName = this.resolveStringValue(factoryBeanName); if (!factoryBeanName.equals(resolvedName)) { beanDefinition.setFactoryBeanName(resolvedName); } } } protected void visitFactoryMethodName(BeanDefinition beanDefinition) { String factoryMethodName = beanDefinition.getFactoryMethodName(); if (factoryMethodName != null) { String resolvedName = this.resolveStringValue(factoryMethodName); if (!factoryMethodName.equals(resolvedName)) { beanDefinition.setFactoryMethodName(resolvedName); } } } protected void visitScope(BeanDefinition beanDefinition) { String scope = beanDefinition.getScope(); if (scope != null) { String resolvedScope = this.resolveStringValue(scope); if (!scope.equals(resolvedScope)) { beanDefinition.setScope(resolvedScope); } } } protected void visitPropertyValues(MutablePropertyValues pvs) { PropertyValue[] pvArray = pvs.getPropertyValues(); PropertyValue[] var3 = pvArray; int var4 = pvArray.length; for(int var5 = 0; var5 < var4; ++var5) { PropertyValue pv = var3[var5]; Object newVal = this.resolveValue(pv.getValue()); if (!ObjectUtils.nullSafeEquals(newVal, pv.getValue())) { pvs.add(pv.getName(), newVal); } } } protected void visitIndexedArgumentValues(Map<Integer, ValueHolder> ias) { Iterator var2 = ias.values().iterator(); while(var2.hasNext()) { ValueHolder valueHolder = (ValueHolder)var2.next(); Object newVal = this.resolveValue(valueHolder.getValue()); if (!ObjectUtils.nullSafeEquals(newVal, valueHolder.getValue())) { valueHolder.setValue(newVal); } } } protected void visitGenericArgumentValues(List<ValueHolder> gas) { Iterator var2 = gas.iterator(); while(var2.hasNext()) { ValueHolder valueHolder = (ValueHolder)var2.next(); Object newVal = this.resolveValue(valueHolder.getValue()); if (!ObjectUtils.nullSafeEquals(newVal, valueHolder.getValue())) { valueHolder.setValue(newVal); } } } protected Object resolveValue(Object value) { if (value instanceof BeanDefinition) { this.visitBeanDefinition((BeanDefinition)value); } else if (value instanceof BeanDefinitionHolder) { this.visitBeanDefinition(((BeanDefinitionHolder)value).getBeanDefinition()); } else { String stringValue; if (value instanceof RuntimeBeanReference) { RuntimeBeanReference ref = (RuntimeBeanReference)value; stringValue = this.resolveStringValue(ref.getBeanName()); if (!stringValue.equals(ref.getBeanName())) { return new RuntimeBeanReference(stringValue); } } else if (value instanceof RuntimeBeanNameReference) { RuntimeBeanNameReference ref = (RuntimeBeanNameReference)value; stringValue = this.resolveStringValue(ref.getBeanName()); if (!stringValue.equals(ref.getBeanName())) { return new RuntimeBeanNameReference(stringValue); } } else if (value instanceof Object[]) { this.visitArray((Object[])((Object[])value)); } else if (value instanceof List) { this.visitList((List)value); } else if (value instanceof Set) { this.visitSet((Set)value); } else if (value instanceof Map) { this.visitMap((Map)value); } else if (value instanceof TypedStringValue) { TypedStringValue typedStringValue = (TypedStringValue)value; stringValue = typedStringValue.getValue(); if (stringValue != null) { String visitedString = this.resolveStringValue(stringValue); typedStringValue.setValue(visitedString); } } else if (value instanceof String) { return this.resolveStringValue((String)value); } } return value; } protected void visitArray(Object[] arrayVal) { for(int i = 0; i < arrayVal.length; ++i) { Object elem = arrayVal[i]; Object newVal = this.resolveValue(elem); if (!ObjectUtils.nullSafeEquals(newVal, elem)) { arrayVal[i] = newVal; } } } protected void visitList(List listVal) { for(int i = 0; i < listVal.size(); ++i) { Object elem = listVal.get(i); Object newVal = this.resolveValue(elem); if (!ObjectUtils.nullSafeEquals(newVal, elem)) { listVal.set(i, newVal); } } } protected void visitSet(Set setVal) { Set newContent = new LinkedHashSet(); boolean entriesModified = false; Object elem; int elemHash; Object newVal; int newValHash; for(Iterator var4 = setVal.iterator(); var4.hasNext(); entriesModified = entriesModified || newVal != elem || newValHash != elemHash) { elem = var4.next(); elemHash = elem != null ? elem.hashCode() : 0; newVal = this.resolveValue(elem); newValHash = newVal != null ? newVal.hashCode() : 0; newContent.add(newVal); } if (entriesModified) { setVal.clear(); setVal.addAll(newContent); } } protected void visitMap(Map<?, ?> mapVal) { Map newContent = new LinkedHashMap(); boolean entriesModified = false; Object key; int keyHash; Object newKey; int newKeyHash; Object val; Object newVal; for(Iterator var4 = mapVal.entrySet().iterator(); var4.hasNext(); entriesModified = entriesModified || newVal != val || newKey != key || newKeyHash != keyHash) { Entry entry = (Entry)var4.next(); key = entry.getKey(); keyHash = key != null ? key.hashCode() : 0; newKey = this.resolveValue(key); newKeyHash = newKey != null ? newKey.hashCode() : 0; val = entry.getValue(); newVal = this.resolveValue(val); newContent.put(newKey, newVal); } if (entriesModified) { mapVal.clear(); mapVal.putAll(newContent); } } protected String resolveStringValue(String strVal) { if (this.valueResolver == null) { throw new IllegalStateException("No StringValueResolver specified - pass a resolver object into the constructor or override the 'resolveStringValue' method"); } else { String resolvedValue = this.valueResolver.resolveStringValue(strVal); return strVal.equals(resolvedValue) ? strVal : resolvedValue; } } }