springboot get请求传递json对象（含值为对象的属性），映射到后台Controller参数实体的 Map 类型字段（含相关关键源码）

修改时间：2020-08-15

假设后台 controller 的参数是一个 User 类型的变量，User 的定义如下：

public class User {
    private String name;
    private int age;
    private List novels;
    private List tags;
    private String[] comments;
    private Blog blog;
    Map params;
}

public class Novel {
    private String name;
    private int size;
}

 

public class Blog {
    private String title;
    private Author author;
}

前台的 json 要使用以下写法：

{
    name: '22',
    'params[age]': '21',
    'params[weight]': 60，
    'tags[1]': 't1',
    'tags[3]': 't3',
    'comments[1]': 'c1',
    'comments[3]': 'c3',
    'blog.title': 'bt1',
    'novels[4].name': 'nv4'
}

如果后台报错说请求链接包含非法字符，则用 encodeURIComponent 编码，或者直接手动写死也行，'[' 是 '%5B'， ']' 是 '%5D'。原因是get请求参数和值都是拼接在URL里的，默认情况下是不允许含有这些字符的。以下是部分关键源码：

以下代码指明了为什么是 '['  ']'  '.'：

// PropertyAccessorUtils.java
private static int getNestedPropertySeparatorIndex(String propertyPath, boolean last) {
    boolean inKey = false;
    int length = propertyPath.length();
    int i = (last ? length - 1 : 0);
    while (last ? i >= 0 : i < length) {
        switch (propertyPath.charAt(i)) {
            case PropertyAccessor.PROPERTY_KEY_PREFIX_CHAR:
            case PropertyAccessor.PROPERTY_KEY_SUFFIX_CHAR:
                inKey = !inKey;
                break;
            case PropertyAccessor.NESTED_PROPERTY_SEPARATOR_CHAR:
                if (!inKey) {
                    return i;
                }
        }
        if (last) {
            i--;
        }
        else {
            i++;
        }
    }
    return -1;
}

// PropertyAccessor.java
public interface PropertyAccessor {
	/**
	 * Path separator for nested properties.
	 * Follows normal Java conventions: getFoo().getBar() would be "foo.bar".
	 */
	String NESTED_PROPERTY_SEPARATOR = ".";

	/**
	 * Path separator for nested properties.
	 * Follows normal Java conventions: getFoo().getBar() would be "foo.bar".
	 */
	char NESTED_PROPERTY_SEPARATOR_CHAR = '.';

	/**
	 * Marker that indicates the start of a property key for an
	 * indexed or mapped property like "person.addresses[0]".
	 */
	String PROPERTY_KEY_PREFIX = "[";

	/**
	 * Marker that indicates the start of a property key for an
	 * indexed or mapped property like "person.addresses[0]".
	 */
	char PROPERTY_KEY_PREFIX_CHAR = '[';

	/**
	 * Marker that indicates the end of a property key for an
	 * indexed or mapped property like "person.addresses[0]".
	 */
	String PROPERTY_KEY_SUFFIX = "]";

	/**
	 * Marker that indicates the end of a property key for an
	 * indexed or mapped property like "person.addresses[0]".
	 */
	char PROPERTY_KEY_SUFFIX_CHAR = ']';
}

以下代码说明了可以处理的集合类型：

// AbstractNestablePropertyAccessor.java
private void processKeyedProperty(PropertyTokenHolder tokens, PropertyValue pv) {
    Object propValue = getPropertyHoldingValue(tokens);
    PropertyHandler ph = getLocalPropertyHandler(tokens.actualName);
    if (ph == null) {
        throw new InvalidPropertyException(
                getRootClass(), this.nestedPath + tokens.actualName, "No property handler found");
    }
    Assert.state(tokens.keys != null, "No token keys");
    String lastKey = tokens.keys[tokens.keys.length - 1];

    if (propValue.getClass().isArray()) {
        Class requiredType = propValue.getClass().getComponentType();
        int arrayIndex = Integer.parseInt(lastKey);
        Object oldValue = null;
        try {
            if (isExtractOldValueForEditor() && arrayIndex < Array.getLength(propValue)) {
                oldValue = Array.get(propValue, arrayIndex);
            }
            Object convertedValue = convertIfNecessary(tokens.canonicalName, oldValue, pv.getValue(),
                    requiredType, ph.nested(tokens.keys.length));
            int length = Array.getLength(propValue);
            if (arrayIndex >= length && arrayIndex < this.autoGrowCollectionLimit) {
                Class componentType = propValue.getClass().getComponentType();
                Object newArray = Array.newInstance(componentType, arrayIndex + 1);
                System.arraycopy(propValue, 0, newArray, 0, length);
                setPropertyValue(tokens.actualName, newArray);
                propValue = getPropertyValue(tokens.actualName);
            }
            Array.set(propValue, arrayIndex, convertedValue);
        }
        catch (IndexOutOfBoundsException ex) {
            throw new InvalidPropertyException(getRootClass(), this.nestedPath + tokens.canonicalName,
                    "Invalid array index in property path '" + tokens.canonicalName + "'", ex);
        }
    }

    else if (propValue instanceof List) {
        Class requiredType = ph.getCollectionType(tokens.keys.length);
        List