掌握Jackson ObjectMapper：自定义JSON美化输出格式

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);
// ... 进行序列化

ObjectMapper mapper = new ObjectMapper();
mapper.setDefaultPrettyPrinter(printer);

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
import com.fasterxml.jackson.core.util.DefaultIndenter;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

// 示例POJO类
class ActionOutput {
    private String key1;
    private List<String> key2;
    private String key3;

    // 全参构造函数
    public ActionOutput(String key1, List<String> key2, String key3) {
        this.key1 = key1;
        this.key2 = key2;
        this.key3 = key3;
    }

    // Getters (Jackson序列化需要)
    public String getKey1() { return key1; }
    public List<String> getKey2() { return key2; }
    public String getKey3() { return key3; }

    // Setters (如果需要反序列化)
    public void setKey1(String key1) { this.key1 = key1; }
    public void setKey2(List<String> key2) { this.key2 = key2; }
    public void setKey3(String key3) { this.key3 = key3; }
}

public class CustomJsonPrettyPrintDemo {

    public static void main(String[] args) throws IOException {
        // 1. 准备数据
        List<ActionOutput> actions = new ArrayList<>();
        actions.add(new ActionOutput("value1", List.of(), null));
        actions.add(new ActionOutput("value2", List.of("itemA", "itemB"), "anotherValue"));
        actions.add(new ActionOutput("value3", List.of(), null));

        // 2. 定制 DefaultPrettyPrinter
        DefaultPrettyPrinter printer = new DefaultPrettyPrinter();
        // 为对象和数组设置缩进器，确保在 [ 和 { 后有换行
        printer.indentObjectsWith(new DefaultIndenter("  ", DefaultIndenter.SYS_LF));
        printer.indentArraysWith(new DefaultIndenter("  ", DefaultIndenter.SYS_LF));

        // 3. 创建 ObjectMapper 并设置自定义打印器
        ObjectMapper mapper = new ObjectMapper();
        // 设置自定义的DefaultPrettyPrinter
        mapper.setDefaultPrettyPrinter(printer);

        // 4. 执行序列化并输出到文件或控制台
        String outputFilePath = "output.json";

        System.out.println("--- 序列化到字符串 ---");
        String jsonRes = mapper
            .writerWithDefaultPrettyPrinter() // 使用配置的默认美化打印器
            .writeValueAsString(actions);
        System.out.println(jsonRes);

        System.out.println("\n--- 序列化到文件: " + outputFilePath + " ---");
        mapper
            .writerWithDefaultPrettyPrinter()
            .writeValue(new File(outputFilePath), actions);
        System.out.println("JSON已写入到 " + outputFilePath);
    }
}

[
  {
    "key1" : "value1",
    "key2" : [ ],
    "key3" : null
  },
  {
    "key1" : "value2",
    "key2" : [
      "itemA",
      "itemB"
    ],
    "key3" : "anotherValue"
  },
  {
    "key1" : "value3",
    "key2" : [ ],
    "key3" : null
  }
]