Java toString() 使用反射？
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Java toString() using reflection?
提问by James McMahon
I was writing a toString() for a class in Java the other day by manually writing out each element of the class to a String and it occurred to me that using reflection it might be possible to create a generic toString() method that could work on ALL classes. I.E. it would figure out the field names and values and send them out to a String.
前几天我正在为 Java 中的一个类编写一个 toString()，通过手动将类的每个元素写入一个 String，我突然想到使用反射可能会创建一个可以工作的通用 toString() 方法在所有课程上。IE 它将找出字段名称和值并将它们发送到字符串。
Getting the field names is fairly simple, here is what a co-worker came up with:
获取字段名称相当简单，这是一位同事提出的：
public static List initFieldArray(String className) throws ClassNotFoundException {
Class c = Class.forName(className);
Field field[] = c.getFields();
List<String> classFields = new ArrayList(field.length);
for (int i = 0; i < field.length; i++) {
String cf = field[i].toString();
classFields.add(cf.substring(cf.lastIndexOf(".") + 1));
}
return classFields;
}
Using a factory I could reduce the performance overhead by storing the fields once, the first time the toString() is called. However finding the values could be a lot more expensive.
使用工厂，我可以通过在第一次调用 toString() 时存储一次字段来降低性能开销。然而，找到这些值可能要贵得多。
Due to the performance of reflection this may be more hypothetical then practical. But I am interested in the idea of reflection and how I can use it to improve my everyday programming.
由于反射的性能，这可能比实际更假设。但我对反射的想法以及如何使用它来改进我的日常编程感兴趣。
采纳答案by krosenvold
Apache commons-lang ReflectionToStringBuilderdoes this for you.
Apache commons-lang ReflectionToStringBuilder为你做这件事。
import org.apache.commons.lang3.builder.ReflectionToStringBuilder
// your code goes here
public String toString() {
return ReflectionToStringBuilder.toString(this);
}
回答by Olivier
If you're using Eclipse, you may also have a look at JUtils toString generator, which does it statically (generating the method in your source code).
如果您使用的是 Eclipse，您还可以查看JUtils toString generator，它是静态的（在源代码中生成方法）。
回答by McDowell
Not reflection, but I had a look at generating the toString method (along with equals/hashCode) as a post-compilation step using bytecode manipulation. Results were mixed.
不是反射，但我查看了使用字节码操作生成 toString 方法（以及 equals/hashCode）作为编译后步骤。结果喜忧参半。
回答by Steve B.
W/reflection, as I hadn't been aware of the apache library:
W/reflection，因为我不知道 apache 库：
(be aware that if you do this you'll probably need to deal with subobjects and make sure they print properly - in particular, arrays won't show you anything useful)
（请注意，如果您这样做，您可能需要处理子对象并确保它们正确打印 - 特别是，数组不会向您显示任何有用的东西）
@Override
public String toString()
{
StringBuilder b = new StringBuilder("[");
for (Field f : getClass().getFields())
{
if (!isStaticField(f))
{
try
{
b.append(f.getName() + "=" + f.get(this) + " ");
} catch (IllegalAccessException e)
{
// pass, don't print
}
}
}
b.append(']');
return b.toString();
}
private boolean isStaticField(Field f)
{
return Modifier.isStatic(f.getModifiers());
}
回答by James McMahon
Here is the Netbeans equivalent to Olivier's answer; smart-codegen plugin for Netbeans.
这是相当于 Olivier 答案的 Netbeans；Netbeans 的智能代码生成插件。
回答by nazar_art
You can use already implemented libraries, as ReflectionToStringBuilderfrom Apache commons-lang. As was mentioned.
您可以使用已经实现的库，如Apache commons-lang 中的ReflectionToStringBuilder。正如所提到的。
Or write smt similar by yourself with reflection API.
或者自己用反射 API编写类似的 smt 。
Here is some example:
下面是一些例子：
class UniversalAnalyzer {
private ArrayList<Object> visited = new ArrayList<Object>();
/**
* Converts an object to a string representation that lists all fields.
* @param obj an object
* @return a string with the object's class name and all field names and
* values
*/
public String toString(Object obj) {
if (obj == null) return "null";
if (visited.contains(obj)) return "...";
visited.add(obj);
Class cl = obj.getClass();
if (cl == String.class) return (String) obj;
if (cl.isArray()) {
String r = cl.getComponentType() + "[]{";
for (int i = 0; i < Array.getLength(obj); i++) {
if (i > 0) r += ",";
Object val = Array.get(obj, i);
if (cl.getComponentType().isPrimitive()) r += val;
else r += toString(val);
}
return r + "}";
}
String r = cl.getName();
// inspect the fields of this class and all superclasses
do {
r += "[";
Field[] fields = cl.getDeclaredFields();
AccessibleObject.setAccessible(fields, true);
// get the names and values of all fields
for (Field f : fields) {
if (!Modifier.isStatic(f.getModifiers())) {
if (!r.endsWith("[")) r += ",";
r += f.getName() + "=";
try {
Class t = f.getType();
Object val = f.get(obj);
if (t.isPrimitive()) r += val;
else r += toString(val);
} catch (Exception e) {
e.printStackTrace();
}
}
}
r += "]";
cl = cl.getSuperclass();
} while (cl != null);
return r;
}
}
回答by Daniel Schmidt
Another option, if you are ok with JSON, is Google's GSON library.
如果您对 JSON 没问题，另一种选择是 Google 的 GSON 库。
public String toString() {
return new GsonBuilder().setPrettyPrinting().create().toJson(this);
}
It's going to do the reflection for you. This produces a nice, easy to read JSON file. Easy-to-read being relative, non tech folks might find the JSON intimidating.
它会为你做反思。这会生成一个漂亮的、易于阅读的 JSON 文件。相对易于阅读，非技术人员可能会发现 JSON 令人生畏。
You could make the GSONBuilder a member variable too, if you don't want to new it up every time.
如果您不想每次都更新它，您也可以将 GSONBuilder 设为成员变量。
If you have data that can't be printed (like a stream) or data you just don't want to print, you can just add @Expose tags to the attributes you want to print and then use the following line.
如果您有无法打印的数据（如流）或您只是不想打印的数据，则只需将 @Expose 标记添加到要打印的属性，然后使用以下行。
new GsonBuilder()
.setPrettyPrinting()
.excludeFieldsWithoutExposeAnnotation()
.create()
.toJson(this);
