如何将 Jackson PrettyPrinter 格式 json 配置为 Gson

Question

Jackson DefaultPrettyPrinter 格式 json 为

{
  "field" : [ 1, 2 ]
}

如何配置它以格式化 json，冒号前没有空格，并且数组的每个元素都像 GSON 那样从新行开始？

{
  "field": [
    1,
    2
  ]
}

Answer 1

我实现了与 GSON 完全一样格式化 json 的 PrettyPrinter

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.util.DefaultIndenter;
import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
import com.fasterxml.jackson.core.util.Separators;

import java.io.IOException;


public class MyPrettyPrinter extends DefaultPrettyPrinter {

    public MyPrettyPrinter() {
        _arrayIndenter = DefaultIndenter.SYSTEM_LINEFEED_INSTANCE;
        _objectIndenter = DefaultIndenter.SYSTEM_LINEFEED_INSTANCE;
    }

    public MyPrettyPrinter(DefaultPrettyPrinter base) {
        super(base);
    }

    @Override
    public MyPrettyPrinter createInstance() {
        if (getClass() != MyPrettyPrinter.class) {
            throw new IllegalStateException("Failed `createInstance()`: " + getClass().getName()
                    + " does not override method; it has to");
        }
        return new MyPrettyPrinter(this);
    }

    @Override
    public MyPrettyPrinter withSeparators(Separators separators) {
        this._separators = separators;
        this._objectFieldValueSeparatorWithSpaces = separators.getObjectFieldValueSeparator() + " ";
        return this;
    }

    @Override
    public void writeEndArray(JsonGenerator g, int nrOfValues) throws IOException {
        if (!_arrayIndenter.isInline()) {
            --_nesting;
        }
        if (nrOfValues > 0) {
            _arrayIndenter.writeIndentation(g, _nesting);
        }
        g.writeRaw(']');
    }

    @Override
    public void writeEndObject(JsonGenerator g, int nrOfEntries) throws IOException {
        if (!_objectIndenter.isInline()) {
            --_nesting;
        }
        if (nrOfEntries > 0) {
            _objectIndenter.writeIndentation(g, _nesting);
        }
        g.writeRaw('}');
    }
}

需要覆盖withSeparators 以删除冒号前的空格。覆盖writeEndArray 和writeEndObject 用于删除空数组和空对象[] {} 中的空间。

Answer 2

我指出的骗子有一些旧信息。我是通过配置DefaultPrettyPrinter做到的：

ObjectMapper om = new ObjectMapper();
DefaultPrettyPrinter dpp = new DefaultPrettyPrinter();
dpp.indentArraysWith(new DefaultIndenter("  ", "\n"));
om.setDefaultPrettyPrinter(dpp);

Answer 3

您最终必须配置编写器，

ObjectMapper mapper = new ObjectMapper();
String String = "{\"field\" : [ 1, 2 ]}";
Object obj = mapper.readValue(String, Object.class);

DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
prettyPrinter.indentArraysWith(DefaultIndenter.SYSTEM_LINEFEED_INSTANCE);

System.out.println(mapper.writer(prettyPrinter).writeValueAsString(obj));

输出

{
  "field" : [
    1,
    2
  ]
}