您可以自定义 Jackson 如何缩进输出。根据您使用的 Jackson 版本,有不同的方法可以实现它。
杰克逊 2.5 和更新版本
请执行下列操作:
DefaultPrettyPrinter printer = new DefaultPrettyPrinter();
Indenter indenter = new DefaultIndenter();
printer.indentObjectsWith(indenter); // Indent JSON objects
printer.indentArraysWith(indenter); // Indent JSON arrays
ObjectMapper mapper = new ObjectMapper();
mapper.writer(printer).writeValue(new FileOutputStream(outputFile), node);
默认情况下,将使用 2 个空格。对于不同数量的空格,使用DefaultIndenter
接收字符串以缩进级别和行分隔符的构造函数:
Indenter indenter = new DefaultIndenter(" ", DefaultIndenter.SYS_LF);
Jackson 2.4 及更早的版本
请执行下列操作:
DefaultPrettyPrinter printer = new DefaultPrettyPrinter();
Indenter indenter = new Lf2SpacesIndenter();
printer.indentObjectsWith(indenter); // Indent JSON objects
printer.indentArraysWith(indenter); // Indent JSON arrays
ObjectMapper mapper = new ObjectMapper();
mapper.writer(printer).writeValue(new FileOutputStream(outputFile), node);
仅限于 2 个空格,Lf2SpacesIndenter
您不能更改它。
如果您需要不同数量的空格,则需要编写自定义实现。DefaultIndenter
这是使用与Jackson 2.5 中引入的相同代码的代码:
/**
* Default linefeed-based indenter.
*/
public class CustomSpaceIndenter extends DefaultPrettyPrinter.NopIndenter {
public final static String SYS_LF;
static {
String lf;
try {
lf = System.getProperty("line.separator");
} catch (Throwable t) {
lf = "\n"; // fallback when security manager denies access
}
SYS_LF = lf;
}
public static final CustomSpaceIndenter SYSTEM_LINEFEED_INSTANCE =
new CustomSpaceIndenter(" ", SYS_LF);
/**
* We expect to rarely get indentation deeper than this number of levels,
* and try not to pre-generate more indentations than needed.
*/
private final static int INDENT_LEVELS = 16;
private final char[] indents;
private final int charsPerLevel;
private final String eol;
/**
* Indent with two spaces and the system's default line feed
*/
public CustomSpaceIndenter() {
this(" ", SYS_LF);
}
/**
* Create an indenter which uses the <code>indent</code> string to indent one level
* and the <code>eol</code> string to separate lines.
*/
public CustomSpaceIndenter(String indent, String eol) {
charsPerLevel = indent.length();
indents = new char[indent.length() * INDENT_LEVELS];
int offset = 0;
for (int i=0; i<INDENT_LEVELS; i++) {
indent.getChars(0, indent.length(), indents, offset);
offset += indent.length();
}
this.eol = eol;
}
public CustomSpaceIndenter withLinefeed(String lf) {
if (lf.equals(eol)) {
return this;
}
return new CustomSpaceIndenter(getIndent(), lf);
}
public CustomSpaceIndenter withIndent(String indent) {
if (indent.equals(getIndent())) {
return this;
}
return new CustomSpaceIndenter(indent, eol);
}
public String getEol() {
return eol;
}
public String getIndent() {
return new String(indents, 0, charsPerLevel);
}
@Override
public boolean isInline() {
return false;
}
@Override
public void writeIndentation(JsonGenerator jg, int level) throws IOException {
jg.writeRaw(eol);
if (level > 0) { // should we err on negative values (as there's some flaw?)
level *= charsPerLevel;
while (level > indents.length) { // unlike to happen but just in case
jg.writeRaw(indents, 0, indents.length);
level -= indents.length;
}
jg.writeRaw(indents, 0, level);
}
}
}
它可以如下使用:
Indenter indenter = new CustomSpaceIndenter(" ", CustomSpaceIndenter.SYS_LF);